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ahalls / GRDB.swift

A versatile SQLite toolkit for Swift, with WAL mode support

Home Page:https://www.sqlite.org

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GRDB.swift Swift Platforms License

GRDB.swift is an SQLite toolkit for Swift 3.0 Preview 1 (June 13, 2016).

It ships with a low-level SQLite API, and high-level tools that help dealing with databases:

  • Records: fetching and persistence methods for your custom structs and class hierarchies
  • Query Interface: a swift way to avoid the SQL language
  • WAL Mode Support: that means extra performance for multi-threaded applications
  • Migrations: transform your database as your application evolves
  • Database Changes Observation: perform post-commit and post-rollback actions
  • Fetched Records Controller: automated tracking of changes in a query results, and UITableView animations
  • Encryption with SQLCipher
  • Support for custom SQLite builds

More than a set of tools that leverage SQLite abilities, GRDB is also:

You should give it a try.

The Swift3 branch has no version. It is currently synced with v0.73.0 of the Swift 2.2 main branch.

Follow @groue on Twitter for release announcements and usage tips.

Requirements: iOS 8.0+ / OSX 10.9+, Xcode 8.0 beta (8S128d)

Usage

Open a connection to the database:

import GRDB
let dbQueue = try DatabaseQueue(path: "/path/to/database.sqlite")

Execute SQL statements:

try dbQueue.inDatabase { db in
    try db.execute(
        "CREATE TABLE pointOfInterests (" +
            "id INTEGER PRIMARY KEY, " +
            "title TEXT, " +
            "favorite BOOLEAN NOT NULL, " +
            "latitude DOUBLE NOT NULL, " +
            "longitude DOUBLE NOT NULL" +
        ")")

    try db.execute(
        "INSERT INTO pointOfInterests (title, favorite, latitude, longitude) " +
        "VALUES (?, ?, ?, ?)",
        arguments: ["Paris", true, 48.85341, 2.3488])
    
    let parisId = db.lastInsertedRowID
}

Fetch database rows and values:

dbQueue.inDatabase { db in
    for row in Row.fetch(db, "SELECT * FROM pointOfInterests") {
        let title: String = row.value(named: "title")
        let isFavorite: Bool = row.value(named: "favorite")
        let coordinate = CLLocationCoordinate2DMake(
            row.value(named: "latitude"),
            row.value(named: "longitude"))
    }

    let poiCount = Int.fetchOne(db, "SELECT COUNT(*) FROM pointOfInterests")! // Int
    let poiTitles = String.fetchAll(db, "SELECT title FROM pointOfInterests") // [String]
}

// Extraction
let poiCount = dbQueue.inDatabase { db in
    Int.fetchOne(db, "SELECT COUNT(*) FROM pointOfInterests")!
}

Insert and fetch records:

struct PointOfInterest {
    var id: Int64?
    var title: String?
    var isFavorite: Bool
    var coordinate: CLLocationCoordinate2D
}

// snip: turn PointOfInterest into a "record" by adopting the protocols that
// provide fetching and persistence methods.

try dbQueue.inDatabase { db in
    var berlin = PointOfInterest(
        id: nil,
        title: "Berlin",
        isFavorite: false,
        coordinate: CLLocationCoordinate2DMake(52.52437, 13.41053))

    try berlin.insert(dbQueue)
    berlin.id // some value

    berlin.isFavorite = true
    try berlin.update(dbQueue)
    
    // Fetch [PointOfInterest] from SQL
    let pois = PointOfInterest.fetchAll(db, "SELECT * FROM pointOfInterests")
}

Avoid SQL with the query interface:

let titleColumn = SQLColumn("title")
let favoriteColumn = SQLColumn("favorite")

dbQueue.inDatabase { db in
    // PointOfInterest?
    let paris = PointOfInterest.fetchOne(db, key: 1)
    
    // PointOfInterest?
    let berlin = PointOfInterest.filter(titleColumn == "Berlin").fetchOne(db)
    
    // [PointOfInterest]
    let favoritePois = PointOfInterest
        .filter(favoriteColumn)
        .order(titleColumn)
        .fetchAll(db)
}

Documentation

GRDB runs on top of SQLite: you should get familiar with the SQLite FAQ. For general and detailed information, jump to the SQLite Documentation.

Getting started

SQLite and SQL

Application tools

Good to know

FAQ

Sample Code

Installation

Manually

  1. Download a copy of GRDB.swift.
  2. Embed the GRDB.xcodeproj project in your own project.
  3. Add the GRDBOSX or GRDBiOS target in the Target Dependencies section of the Build Phases tab of your application target.
  4. Add GRDB.framework to the Embedded Binaries section of the General tab of your target.

See GRDBDemoiOS for an example of such integration.

Custom SQLite builds

By default, GRDB uses the SQLite library that ships with the operating system. You can build GRDB with custom SQLite sources and options, through swiftlyfalling/SQLiteLib. See installation instructions.

Database Connections

GRDB provides two classes for accessing SQLite databases: DatabaseQueue and DatabasePool:

import GRDB

// Pick one:
let dbQueue = try DatabaseQueue(path: "/path/to/database.sqlite")
let dbPool = try DatabasePool(path: "/path/to/database.sqlite")

The differences are:

  • Database pools allow concurrent database accesses (this can improve the performance of multithreaded applications).
  • Unless read-only, database pools open your SQLite database in the WAL mode.
  • Database queues support in-memory databases.

If you are not sure, choose DatabaseQueue. You will always be able to switch to DatabasePool later.

Database Queues

Open a database queue with the path to a database file:

import GRDB

let dbQueue = try DatabaseQueue(path: "/path/to/database.sqlite")
let inMemoryDBQueue = DatabaseQueue()

SQLite creates the database file if it does not already exist. The connection is closed when the database queue gets deallocated.

A database queue can be used from any thread. The inDatabase and inTransaction methods block the current thread until your database statements are executed in a protected dispatch queue. They safely serialize the database accesses:

// Execute database statements:
try dbQueue.inDatabase { db in
    try db.execute("CREATE TABLE pointOfInterests (...)")
    try PointOfInterest(...).insert(db)
}

// Wrap database statements in a transaction:
try dbQueue.inTransaction { db in
    if let poi = PointOfInterest.fetchOne(db, key: 1) {
        try poi.delete(db)
    }
    return .commit
}

// Read values:
dbQueue.inDatabase { db in
    let pois = PointOfInterest.fetchAll(db)
    let poiCount = PointOfInterest.fetchCount(db)
}

// Extract a value from the database:
let poiCount = dbQueue.inDatabase { db in
    PointOfInterest.fetchCount(db)
}

Your application should create a single DatabaseQueue per database file. See, for example, DemoApps/GRDBDemoiOS/Database.swift for a sample code that properly sets up a single database queue that is available throughout the application.

If you do otherwise, you may well experience concurrency issues, and you don't want that. See Concurrency for more information.

Configure database queues:

var config = Configuration()
config.readonly = true
config.foreignKeysEnabled = true // The default is already true
config.trace = { print($0) }     // Prints all SQL statements
config.fileAttributes = [FileAttributeKey.protectionKey.rawValue: ...]  // Configure database protection

let dbQueue = try DatabaseQueue(
    path: "/path/to/database.sqlite",
    configuration: config)

See Configuration for more details.

Database Pools

Database Queues are simple, but they prevent concurrent accesses: at every moment, there is no more than a single thread that is using the database.

A Database Pool can improve your application performance because it allows concurrent database accesses.

import GRDB
let dbPool = try DatabasePool(path: "/path/to/database.sqlite")

SQLite creates the database file if it does not already exist. The connection is closed when the database pool gets deallocated.

☝️ Note: unless read-only, a database pool opens your database in the SQLite "WAL mode". The WAL mode does not fit all situations. Please have a look at https://www.sqlite.org/wal.html.

A database pool can be used from any thread. The read, write and writeInTransaction methods block the current thread until your database statements are executed in a protected dispatch queue. They safely isolate the database accesses:

// Execute database statements:
try dbPool.write { db in
    try db.execute("CREATE TABLE pointOfInterests (...)")
    try PointOfInterest(...).insert(db)
}

// Wrap database statements in a transaction:
try dbPool.writeInTransaction { db in
    if let poi = PointOfInterest.fetchOne(db, key: 1) {
        try poi.delete(db)
    }
    return .commit
}

// Read values:
dbPool.read { db in
    let pois = PointOfInterest.fetchAll(db)
    let poiCount = PointOfInterest.fetchCount(db)
}

// Extract a value from the database:
let poiCount = dbPool.read { db in
    PointOfInterest.fetchCount(db)
}

Your application should create a single DatabasePool per database file.

If you do otherwise, you may well experience concurrency issues, and you don't want that. See Concurrency for more information.

Database pools allows several threads to access the database at the same time:

  • When you don't need to modify the database, prefer the read method, because several threads can perform reads in parallel.

  • The total number of concurrent reads is limited. When the maximum number has been reached, a read waits for another read to complete. That maximum number can be configured (see below).

  • Conversely, writes are serialized. They still can happen in parallel with reads, but GRDB makes sure that those parallel writes are not visible inside a read closure.

See Concurrency for more information.

Configure database pools:

var config = Configuration()
config.readonly = true
config.foreignKeysEnabled = true // The default is already true
config.trace = { print($0) }     // Prints all SQL statements
config.fileAttributes = [FileAttributeKey.protectionKey.rawValue: ...]  // Configure database protection
condig.maximumReaderCount = 10   // The default is 5

let dbPool = try DatabasePool(
    path: "/path/to/database.sqlite",
    configuration: config)

See Configuration for more details.

Database pools are more memory-hungry than database queues. See Memory Management for more information.

SQLite API

In this section of the documentation, we will talk SQL only. Jump to the query interface if SQL if not your cup of tea.

Advanced topics:

Executing Updates

Once granted with a database connection, the execute method executes the SQL statements that do not return any database row, such as CREATE TABLE, INSERT, DELETE, ALTER, etc.

For example:

try db.execute(
    "CREATE TABLE persons (" +
        "id INTEGER PRIMARY KEY," +
        "name TEXT NOT NULL," +
        "age INT" +
    ")")

try db.execute(
    "INSERT INTO persons (name, age) VALUES (:name, :age)",
    arguments: ["name": "Barbara", "age": 39])

// Join multiple statements with a semicolon:
try db.execute(
    "INSERT INTO persons (name, age) VALUES (?, ?); " +
    "INSERT INTO persons (name, age) VALUES (?, ?)",
    arguments: ["Arthur", 36, "Barbara", 39])

The ? and colon-prefixed keys like :name in the SQL query are the statements arguments. You pass arguments with arrays or dictionaries, as in the example above. See Values for more information on supported arguments types (Bool, Int, String, Date, Swift enums, etc.).

Never ever embed values directly in your SQL strings, and always use arguments instead. See Avoiding SQL Injection for more information.

After an INSERT statement, you can get the row ID of the inserted row:

try db.execute(
    "INSERT INTO persons (name, age) VALUES (?, ?)",
    arguments: ["Arthur", 36])
let personId = db.lastInsertedRowID

Don't miss Records, that provide classic persistence methods:

let person = Person(name: "Arthur", age: 36)
try person.insert(db)
let personId = person.id

Fetch Queries

You can fetch database rows, plain values, and custom models aka "records".

Rows are the raw results of SQL queries:

if let row = Row.fetchOne(db, "SELECT * FROM wines WHERE id = ?", arguments: [1]) {
    let name: String = row.value(named: "name")
    let color: Color = row.value(named: "color")
    print(name, color)
}

Values are the Bool, Int, String, Date, Swift enums, etc. stored in row columns:

for url in URL.fetch(db, "SELECT url FROM wines") {
    print(url)
}

Records are your application objects that can initialize themselves from rows:

let wines = Wine.fetchAll(db, "SELECT * FROM wines")

Fetching Methods

Throughout GRDB, you can always fetch sequences, arrays, or single values of any fetchable type (database row, simple value, or custom record):

Type.fetch(...)    // DatabaseSequence<Type>
Type.fetchAll(...) // [Type]
Type.fetchOne(...) // Type?

  • fetch returns a sequence that is memory efficient, but must be consumed in a protected dispatch queue (you'll get a fatal error if you do otherwise).

    for row in Row.fetch(db, "SELECT ...") { // DatabaseSequence<Row>
    ...
}

    Don't modify the database during a sequence iteration:

    // Undefined behavior
for row in Row.fetch(db, "SELECT * FROM persons") {
    try db.execute("DELETE FROM persons ...")
}

    A sequence fetches a new set of results each time it is iterated.

  • fetchAll returns an array that can be consumed on any thread. It contains copies of database values, and can take a lot of memory:

    let persons = Person.fetchAll(db, "SELECT ...") // [Person]

  • fetchOne returns a single optional value, and consumes a single database row (if any).

    let count = Int.fetchOne(db, "SELECT COUNT(*) ...") // Int?

Row Queries

Fetching Rows

Fetch sequences of rows, arrays, or single rows (see fetching methods):

Row.fetch(db, "SELECT ...", arguments: ...)     // DatabaseSequence<Row>
Row.fetchAll(db, "SELECT ...", arguments: ...)  // [Row]
Row.fetchOne(db, "SELECT ...", arguments: ...)  // Row?

for row in Row.fetch(db, "SELECT * FROM wines") {
    let name: String = row.value(named: "name")
    let color: Color = row.value(named: "color")
    print(name, color)
}

Arguments are optional arrays or dictionaries that fill the positional ? and colon-prefixed keys like :name in the query:

let rows = Row.fetchAll(db,
    "SELECT * FROM persons WHERE name = ?",
    arguments: ["Arthur"])

let rows = Row.fetchAll(db,
    "SELECT * FROM persons WHERE name = :name",
    arguments: ["name": "Arthur"])

See Values for more information on supported arguments types (Bool, Int, String, Date, Swift enums, etc.).

Unlike row arrays that contain copies of the database rows, row sequences are close to the SQLite metal, and require a little care:

☝️ Don't turn a row sequence into an array with Array(rowSequence) or rowSequence.filter { ... }: you would not get the distinct rows you expect. To get an array, use Row.fetchAll(...).

☝️ Make sure you copy a row whenever you extract it from a sequence for later use: row.copy().

Column Values

Read column values by index or column name:

let name: String = row.value(atIndex: 0)    // 0 is the leftmost column
let name: String = row.value(named: "name") // leftmost matching column - lookup is case-insensitive

Make sure to ask for an optional when the value may be NULL:

let name: String? = row.value(named: "name")

The value function returns the type you ask for. See Values for more information on supported value types:

let bookCount: Int     = row.value(named: "bookCount")
let bookCount64: Int64 = row.value(named: "bookCount")
let hasBooks: Bool     = row.value(named: "bookCount")  // false when 0

let string: String     = row.value(named: "date")       // "2015-09-11 18:14:15.123"
let date: Date         = row.value(named: "date")       // Date
self.date = row.value(named: "date") // Depends on the type of the property.

You can also use the as type casting operator:

row.value(...) as Int
row.value(...) as Int?

⚠️ Warning: avoid the as! and as? operators (see rdar://21676393):

row.value(...) as! Int   // NO NO NO DON'T DO THAT!
row.value(...) as? Int   // NO NO NO DON'T DO THAT!

Generally speaking, you can extract the type you need, provided it can be converted from the underlying SQLite value:

  • Successful conversions include:

    • Numeric SQLite values to numeric Swift types, and Bool (zero is the only false boolean).
    • Text SQLite values to Swift String.
    • Blob SQLite values to Foundation Data.

    See Values for more information on supported types (Bool, Int, String, Date, Swift enums, etc.)

  • NULL returns nil.

    let row = Row.fetchOne(db, "SELECT NULL")!
row.value(atIndex: 0) as Int? // nil
row.value(atIndex: 0) as Int  // fatal error: could not convert NULL to Int.

  • Missing columns return nil.

    let row = Row.fetchOne(db, "SELECT 'foo' AS foo")!
row.value(named: "missing") as String? // nil
row.value(named: "missing") as String  // fatal error: no such column: missing

    You can explicitly check for a column presence with the hasColumn method.

  • Invalid conversions throw a fatal error.

    let row = Row.fetchOne(db, "SELECT 'foo'")!
row.value(atIndex: 0) as String // "foo"
row.value(atIndex: 0) as Date?  // fatal error: could not convert "foo" to Date.
row.value(atIndex: 0) as Date   // fatal error: could not convert "foo" to Date.

    This fatal error can be avoided with the DatabaseValueConvertible.fromDatabaseValue() method.

  • SQLite has a weak type system, and provides convenience conversions that can turn Blob to String, String to Int, etc.

    GRDB will sometimes let those conversions go through:

    for row in Row.fetch(db, "SELECT 'foo'") {
    row.value(atIndex: 0) as Int   // 0
}

    Don't freak out: those conversions did not prevent SQLite from becoming the immensely successful database engine you want to use. And GRDB adds safety checks described just above. You can also prevent those convenience conversions altogether by using the DatabaseValue type.

DatabaseValue

DatabaseValue is an intermediate type between SQLite and your values, which gives information about the raw value stored in the database.

let dbv = row.databaseValue(atIndex: 0)    // 0 is the leftmost column
let dbv = row.databaseValue(named: "name") // leftmost matching column - lookup is case-insensitive

// Check for NULL:
dbv.isNull    // Bool

// All the five storage classes supported by SQLite:
switch dbv.storage {
case .null:                 print("NULL")
case .int64(let int64):     print("Int64: \(int64)")
case .double(let double):   print("Double: \(double)")
case .string(let string):   print("String: \(string)")
case .blob(let data):       print("Data: \(data)")
}

You can extract values (Bool, Int, String, Date, Swift enums, etc.) from DatabaseValue, just like you do from rows:

let dbv = row.databaseValue(named: "bookCount")
let bookCount: Int     = dbv.value()
let bookCount64: Int64 = dbv.value()
let hasBooks: Bool     = dbv.value() // false when 0

let dbv = row.databaseValue(named: "date")
let string: String = dbv.value()     // "2015-09-11 18:14:15.123"
let date: Date     = dbv.value()     // Date
self.date          = dbv.value()     // Depends on the type of the property.

Invalid conversions from non-NULL values raise a fatal error. This fatal error can be avoided with the DatabaseValueConvertible.fromDatabaseValue() method:

let row = Row.fetchOne(db, "SELECT 'foo'")!
let dbv = row.databaseValue(at: 0)
let string = dbv.value() as String  // "foo"
let date = dbv.value() as Date?     // fatal error: could not convert "foo" to Date.
let date = Date.fromDatabaseValue(dbv) // nil

Rows as Dictionaries

Row adopts the standard CollectionType protocol, and can be seen as a dictionary of DatabaseValue:

// All the (columnName, databaseValue) tuples, from left to right:
for (columnName, databaseValue) in row {
    ...
}

You can build rows from dictionaries (standard Swift dictionaries and NSDictionary). See Values for more information on supported types:

let row = Row(["name": "foo", "date": nil])

Yet rows are not real dictionaries, because they may contain duplicate keys:

let row = Row.fetchOne(db, "SELECT 1 AS foo, 2 AS foo")!
row.columnNames     // ["foo", "foo"]
row.databaseValues  // [1, 2]
row.databaseValue(named: "foo") // 1 (the value for the leftmost column "foo")
for (columnName, databaseValue) in row { ... } // ("foo", 1), ("foo", 2)

Value Queries

Instead of rows, you can directly fetch values. Like rows, fetch them as sequences, arrays, or single values (see fetching methods). Values are extracted from the leftmost column of the SQL queries:

Int.fetch(db, "SELECT ...", arguments: ...)     // DatabaseSequence<Int>
Int.fetchAll(db, "SELECT ...", arguments: ...)  // [Int]
Int.fetchOne(db, "SELECT ...", arguments: ...)  // Int?

// When database may contain NULL:
Optional<Int>.fetch(db, "SELECT ...", arguments: ...)    // DatabaseSequence<Int?>
Optional<Int>.fetchAll(db, "SELECT ...", arguments: ...) // [Int?]

fetchOne returns an optional value which is nil in two cases: either the SELECT statement yielded no row, or one row with a NULL value.

There are many supported value types (Bool, Int, String, Date, Swift enums, etc.). See Values for more information:

let count = Int.fetchOne(db, "SELECT COUNT(*) FROM persons")! // Int
let urls = URL.fetchAll(db, "SELECT url FROM links")          // [URL]

Values

GRDB ships with built-in support for the following value types:

Values can be used as statement arguments:

let url: URL = ...
let verified: Bool = ...
try db.execute(
    "INSERT INTO links (url, verified) VALUES (?, ?)",
    arguments: [url, verified])

Values can be extracted from rows:

for row in Row.fetch(db, "SELECT * FROM links") {
    let url: URL = row.value(named: "url")
    let verified: Bool = row.value(named: "verified")
}

Values can be directly fetched:

let urls = URL.fetchAll(db, "SELECT url FROM links")  // [URL]

Use values in Records:

class Link : Record {
    var url: URL
    var verified: Bool
    
    required init(row: Row) {
        url = row.value("url")
        verified = row.value("verified")
        super.init(row: row)
    }
    
    override var persistentDictionary: [String: DatabaseValueConvertible?] {
        return ["url": url, "verified": verified]
    }
}

Use values in the query interface:

let url: URL = ...
let link = Link.filter(urlColumn == url).fetchOne(db)

Data (and Memory Savings)

Data suits the BLOB SQLite columns. It can be stored and fetched from the database just like other value types.

Yet, when extracting Data from a row, you have the opportunity to save memory by not copying the data fetched by SQLite, using the dataNoCopy() method:

for row in Row.fetch(db, "SELECT data, ...") {
    let data = row.dataNoCopy(named: "data")     // Data?
}

☝️ Note: the non-copied data does not live longer than the iteration step: make sure that you do not use it past this point.

Compare with the anti-patterns below:

for row in Row.fetch(db, "SELECT data, ...") {
    // This data is copied:
    let data: Data = row.value(named: "data")
    
    // This data is copied:
    if let databaseValue = row.databaseValue(named: "data") {
        let data: Data = databaseValue.value()
    }
    
    // This data is copied:
    let copiedRow = row.copy()
    let data = copiedRow.dataNoCopy(named: "data")
}

// All rows have been copied when the loop begins:
let rows = Row.fetchAll(db, "SELECT data, ...") // [Row]
for row in rows {
    // Too late to do the right thing:
    let data = row.dataNoCopy(named: "data")
}

Date and DateComponents

Date and DateComponents can be stored and fetched from the database.

Here is the support provided by GRDB for the various date formats supported by SQLite:

SQLite format Date DateComponents
YYYY-MM-DD Read ¹ Read/Write
YYYY-MM-DD HH:MM Read ¹ Read/Write
YYYY-MM-DD HH:MM:SS Read ¹ Read/Write
YYYY-MM-DD HH:MM:SS.SSS Read/Write ¹ Read/Write
YYYY-MM-DDTHH:MM Read ¹ Read
YYYY-MM-DDTHH:MM:SS Read ¹ Read
YYYY-MM-DDTHH:MM:SS.SSS Read ¹ Read
HH:MM Read/Write
HH:MM:SS Read/Write
HH:MM:SS.SSS Read/Write
Julian Day Number Read ²
now

¹ Dates are stored and read in the UTC time zone. Missing components are assumed to be zero.

² See https://en.wikipedia.org/wiki/Julian_day

Date

GRDB stores Date using the format "yyyy-MM-dd HH:mm:ss.SSS" in the UTC time zone. It is precise to the millisecond.

This format may not fit your needs. We provide below some sample code for storing dates as timestamps that you can adapt for your application.

Date can be stored and fetched from the database just like other value types:

try db.execute(
    "INSERT INTO persons (creationDate, ...) VALUES (?, ...)",
    arguments: [Date(), ...])

DateComponents

DateComponents is indirectly supported, through the DatabaseDateComponents helper type.

DatabaseDateComponents reads date components from all date formats supported by SQLite, and stores them in the format of your choice, from HH:MM to YYYY-MM-DD HH:MM:SS.SSS.

DatabaseDateComponents can be stored and fetched from the database just like other value types:

let components = DateComponents()
components.year = 1973
components.month = 9
components.day = 18

// Store "1973-09-18"
let dbComponents = DatabaseDateComponents(components, format: .YMD)
try db.execute(
    "INSERT INTO persons (birthDate, ...) VALUES (?, ...)",
    arguments: [dbComponents, ...])

// Read "1973-09-18"
let row = Row.fetchOne(db, "SELECT birthDate ...")!
let dbComponents: DatabaseDateComponents = row.value(named: "birthDate")
dbComponents.format         // .YMD (the actual format found in the database)
dbComponents.dateComponents // DateComponents

NSNumber and NSDecimalNumber

NSNumber can be stored and fetched from the database just like other values. Floating point NSNumbers are stored as Double. Integer and boolean, as Int64. Integers that don't fit Int64 won't be stored: you'll get a fatal error instead. Be cautious when an NSNumber contains an UInt64, for example.

NSDecimalNumber deserves a longer discussion:

SQLite has no support for decimal numbers. Given the table below, SQLite will actually store integers or doubles:

CREATE TABLE transfers (
    amount DECIMAL(10,5) -- will store integer or double, actually
)

This means that computations will not be exact:

try db.execute("INSERT INTO transfers (amount) VALUES (0.1)")
try db.execute("INSERT INTO transfers (amount) VALUES (0.2)")
let sum = NSDecimalNumber.fetchOne(db, "SELECT SUM(amount) FROM transfers")!

// Yikes! 0.3000000000000000512
print(sum)

Don't blame SQLite or GRDB, and instead store your decimal numbers differently.

A classic technique is to store integers instead, since SQLite performs exact computations of integers. For example, don't store Euros, but store cents instead:

// Store
let amount = NSDecimalNumber(string: "0.1")                       // 0.1
let integerAmount = amount.multiplying(byPowerOf10: 2).int64Value // 100
try db.execute("INSERT INTO transfers (amount) VALUES (?)", arguments: [integerAmount])

// Read
let integerAmount = Int64.fetchOne(db, "SELECT SUM(amount) FROM transfers")!    // 100
let amount = NSDecimalNumber(value: integerAmount).multiplying(byPowerOf10: -2) // 0.1

UUID

UUID can be stored and fetched from the database just like other values. GRDB stores uuids as 16-bytes data blobs.

Swift Enums

Swift enums and generally all types that adopt the RawRepresentable protocol can be stored and fetched from the database just like their raw values:

enum Color : Int {
    case red, white, rose
}

enum Grape : String {
    case chardonnay, merlot, riesling
}

// Declare DatabaseValueConvertible adoption
extension Color : DatabaseValueConvertible { }
extension Grape : DatabaseValueConvertible { }

// Store
try db.execute(
    "INSERT INTO wines (grape, color) VALUES (?, ?)",
    arguments: [Grape.merlot, Color.red])

// Read
for rows in Row.fetch(db, "SELECT * FROM wines") {
    let grape: Grape = row.value(named: "grape")
    let color: Color = row.value(named: "color")
}

When a database value does not match any enum case, you get a fatal error. This fatal error can be avoided with the DatabaseValueConvertible.fromDatabaseValue() method:

let row = Row.fetchOne(db, "SELECT 'syrah'")!

row.value(atIndex: 0) as String  // "syrah"
row.value(atIndex: 0) as Grape?  // fatal error: could not convert "syrah" to Grape.
row.value(atIndex: 0) as Grape   // fatal error: could not convert "syrah" to Grape.

let dbv = row.databaseValue(atIndex: 0)
dbv.value() as String           // "syrah"
dbv.value() as Grape?           // fatal error: could not convert "syrah" to Grape.
Grape.fromDatabaseValue(dbv)    // nil

Transactions and Savepoints

The DatabaseQueue.inTransaction() and DatabasePool.writeInTransaction() methods open an SQLite transaction and run their closure argument in a protected dispatch queue. They block the current thread until your database statements are executed:

try dbQueue.inTransaction { db in
    let wine = Wine(color: .red, name: "Pomerol")
    try wine.insert(db)
    return .commit
}

If an error is thrown within the transaction body, the transaction is rollbacked and the error is rethrown by the inTransaction method. If you return .rollback from your closure, the transaction is also rollbacked, but no error is thrown.

If you want to insert a transaction between other database statements, you can use the Database.inTransaction() function:

try dbQueue.inDatabase { db in  // or dbPool.write { db in
    ...
    try db.inTransaction {
        ...
        return .commit
    }
    ...
}

You can ask a database if a transaction is currently opened:

func myCriticalMethod(_ db: Database) throws {
    precondition(db.isInsideTransaction, "This method requires a transaction")
    try ...
}

Yet, you have a better option than checking for transactions: critical sections of your application should use savepoints, described below:

func myCriticalMethod(_ db: Database) throws {
    try db.inSavepoint {
        // Here the database is guaranteed to be inside a transaction.
        try ...
    }
}

Savepoints

Statements grouped in a savepoint can be rollbacked without invalidating a whole transaction:

try dbQueue.inTransaction { db in
    try db.inSavepoint { 
        try db.execute("DELETE ...")
        try db.execute("INSERT ...") // need to rollback the delete above if this fails
        return .commit
    }
    
    // Other savepoints, etc...
    return .commit
}

If an error is thrown within the savepoint body, the savepoint is rollbacked and the error is rethrown by the inSavepoint method. If you return .rollback from your closure, the body is also rollbacked, but no error is thrown.

Unlike transactions, savepoints can be nested. They implicitly open a transaction if no one was opened when the savepoint begins. As such, they behave just like nested transactions. Yet the database changes are only committed to disk when the outermost savepoint is committed:

try dbQueue.inDatabase { db in
    try db.inSavepoint {
        ...
        try db.inSavepoint {
            ...
            return .commit
        }
        ...
        return .commit  // writes changes to disk
    }
}

SQLite savepoints are more than nested transactions, though. For advanced savepoints uses, use SQL queries.

Transaction Kinds

SQLite supports three kinds of transactions: deferred, immediate, and exclusive. GRDB defaults to immediate.

The transaction kind can be changed in the database configuration, or for each transaction:

// A connection with default DEFERRED transactions:
var config = Configuration()
config.defaultTransactionKind = .deferred
let dbQueue = try DatabaseQueue(path: "...", configuration: config)

// Opens a DEFERRED transaction:
dbQueue.inTransaction { db in ... }

// Opens an EXCLUSIVE transaction:
dbQueue.inTransaction(.exclusive) { db in ... }

Custom Value Types

Conversion to and from the database is based on the DatabaseValueConvertible protocol:

public protocol DatabaseValueConvertible {
    /// Returns a value that can be stored in the database.
    var databaseValue: DatabaseValue { get }
    
    /// Returns a value initialized from databaseValue, if possible.
    static func fromDatabaseValue(_ databaseValue: DatabaseValue) -> Self?
}

All types that adopt this protocol can be used like all other value types (Bool, Int, String, Date, Swift enums, etc.)

The databaseValue property returns DatabaseValue, a type that wraps the five values supported by SQLite: NULL, Int64, Double, String and Data. DatabaseValue has no public initializer: to create one, use DatabaseValue.null, or another type that already adopts the protocol: 1.databaseValue, "foo".databaseValue, etc.

The fromDatabaseValue() factory method returns an instance of your custom type if the databaseValue contains a suitable value. If the databaseValue does not contain a suitable value, such as "foo" for Date, the method returns nil.

As an example, see DatabaseTimestamp.playground: it shows how to store dates as timestamps, unlike the built-in Date.

Prepared Statements

Prepared Statements let you prepare an SQL query and execute it later, several times if you need, with different arguments.

There are two kinds of prepared statements: select statements, and update statements:

try dbQueue.inDatabase { db in
    let updateSQL = "INSERT INTO persons (name, age) VALUES (:name, :age)"
    let updateStatement = try db.makeUpdateStatement(updateSQL)
    
    let selectSQL = "SELECT * FROM persons WHERE name = ?"
    let selectStatement = try db.makeSelectStatement(selectSQL)
}

The ? and colon-prefixed keys like :name in the SQL query are the statement arguments. You set them with arrays or dictionaries (arguments are actually of type StatementArguments, which happens to adopt the ArrayLiteralConvertible and DictionaryLiteralConvertible protocols).

updateStatement.arguments = ["name": "Arthur", "age": 41]
selectStatement.arguments = ["Arthur"]

After arguments are set, you can execute the prepared statement:

try updateStatement.execute()

Select statements can be used wherever a raw SQL query string would fit (see fetch queries):

for row in Row.fetch(selectStatement) { ... }
let persons = Person.fetchAll(selectStatement)
let person = Person.fetchOne(selectStatement)

You can set the arguments at the moment of the statement execution:

try updateStatement.execute(arguments: ["name": "Arthur", "age": 41])
let person = Person.fetchOne(selectStatement, arguments: ["Arthur"])

☝️ Note: a prepared statement that has failed can not be reused.

See row queries, value queries, and Records for more information.

Prepared Statements Cache

When the same query will be used several times in the lifetime of your application, you may feel a natural desire to cache prepared statements.

Don't cache statements yourself.

☝️ Note: This is because you don't have the necessary tools. Statements are tied to specific SQLite connections and dispatch queues which you don't manage yourself, especially when you use database pools. A change in the database schema may, or may not invalidate a statement. On systems earlier than iOS 8.2 and OSX 10.10 that don't have the sqlite3_close_v2 function, SQLite connections won't close properly if statements have been kept alive.

Instead, use the cachedUpdateStatement and cachedSelectStatement methods. GRDB does all the hard caching and memory management stuff for you:

let updateStatement = try db.cachedUpdateStatement(updateSQL)
let selectStatement = try db.cachedSelectStatement(selectSQL)

Custom SQL Functions

SQLite lets you define SQL functions.

A custom SQL function extends SQLite. It can be used in raw SQL queries. And when SQLite needs to evaluate it, it calls your custom code.

let reverseString = DatabaseFunction(
    "reverseString",  // The name of the function
    argumentCount: 1, // Number of arguments
    pure: true,       // True means that the result only depends on input
    function: { (databaseValues: [DatabaseValue]) in
        // Extract string value, if any...
        guard let string = String.fromDatabaseValue(databaseValues[0]) else {
            return nil
        }
        // ... and return reversed string:
        return String(string.characters.reversed())
    })
dbQueue.add(function: reverseString)   // Or dbPool.add(function: ...)

dbQueue.inDatabase { db in
    // "oof"
    String.fetchOne(db, "SELECT reverseString('foo')")!
}

The function argument takes an array of DatabaseValue, and returns any valid value (Bool, Int, String, Date, Swift enums, etc.) The number of database values is guaranteed to be argumentCount.

SQLite has the opportunity to perform additional optimizations when functions are "pure", which means that their result only depends on their arguments. So make sure to set the pure argument to true when possible.

Functions can take a variable number of arguments:

When you don't provide any explicit argumentCount, the function can take any number of arguments:

let averageOf = DatabaseFunction("averageOf", pure: true) { (databaseValues: [DatabaseValue]) in
    let doubles = databaseValues.flatMap { Double.fromDatabaseValue($0) }
    return doubles.reduce(0, combine: +) / Double(doubles.count)
}
dbQueue.add(function: averageOf)

dbQueue.inDatabase { db in
    // 2.0
    Double.fetchOne(db, "SELECT averageOf(1, 2, 3)")!
}

Use custom functions in the query interface:

// SELECT reverseString("name") FROM persons
Person.select(reverseString.apply(nameColumn))

GRDB ships with built-in SQL functions that perform unicode-aware string transformations. See Unicode.

Database Schema Introspection

SQLite provides database schema introspection tools, such as the sqlite_master table, and the pragma table_info:

try db.execute("CREATE TABLE persons(id INTEGER PRIMARY KEY, name TEXT)")

// <Row type:"table" name:"persons" tbl_name:"persons" rootpage:2
//      sql:"CREATE TABLE persons(id INTEGER PRIMARY KEY, name TEXT)">
for row in Row.fetch(db, "SELECT * FROM sqlite_master") {
    print(row)
}

// <Row cid:0 name:"id" type:"INTEGER" notnull:0 dflt_value:NULL pk:1>
// <Row cid:1 name:"name" type:"TEXT" notnull:0 dflt_value:NULL pk:0>
for row in Row.fetch(db, "PRAGMA table_info('persons')") {
    print(row)
}

GRDB provides two high-level methods as well:

db.tableExists("persons")    // Bool, true if the table exists
try db.primaryKey("persons") // PrimaryKey?, throws if the table does not exist

Primary key is nil when table has no primary key:

// CREATE TABLE items (name TEXT)
let itemPk = try db.primaryKey("items") // nil

Primary keys have one or several columns. Single-column primary keys may contain the auto-incremented row id:

// CREATE TABLE persons (
//   id INTEGER PRIMARY KEY,
//   name TEXT
// )
let personPk = try db.primaryKey("persons")!
personPk.columns     // ["id"]
personPk.rowIDColumn // "id"

// CREATE TABLE countries (
//   isoCode TEXT NOT NULL PRIMARY KEY
//   name TEXT
// )
let countryPk = db.primaryKey("countries")!
countryPk.columns     // ["isoCode"]
countryPk.rowIDColumn // nil

// CREATE TABLE citizenships (
//   personID INTEGER NOT NULL REFERENCES persons(id)
//   countryIsoCode TEXT NOT NULL REFERENCES countries(isoCode)
//   PRIMARY KEY (personID, countryIsoCode)
// )
let citizenshipsPk = db.primaryKey("citizenships")!
citizenshipsPk.columns     // ["personID", "countryIsoCode"]
citizenshipsPk.rowIDColumn // nil

Row Adapters

Row adapters let you map column names for easier row consumption.

They basically help two incompatible row interfaces to work together. For example, a row consumer expects a column named "consumed", but the produced row has a column named "produced":

// An adapter that maps column 'consumed' to column 'produced':
let adapter = ColumnMapping(["consumed": "produced"])

// Fetch a column named 'produced', and apply adapter:
let row = Row.fetchOne(db, "SELECT 'Hello' AS produced", adapter: adapter)!

// The adapter in action:
row.value(named: "consumed") // "Hello"

Row adapters can also define row variants. Variants help several consumers feed on a single row and can reveal useful with joined queries.

For example, let's build a query which loads books along with their author:

let sql = "SELECT books.id, books.title, " +
          "       books.authorID, persons.name AS authorName " +
          "FROM books " +
          "JOIN persons ON books.authorID = persons.id"

The author columns are "authorID" and "authorName". Let's say that we prefer to consume them as "id" and "name". For that we build an adapter which defines a variant named "author":

let authorMapping = ColumnMapping(["id": "authorID", "name": "authorName"])
let adapter = VariantRowAdapter(variants: ["author": authorMapping])

Use the Row.variant(named:) method to load the "author" variant:

for row in Row.fetch(db, sql, adapter: adapter) {
    // The fetched row, without adaptation:
    row.value(named: "id")          // 1
    row.value(named: "title")       // Moby-Dick
    row.value(named: "authorID")    // 10
    row.value(named: "authorName")  // Melville
    
    // The "author" variant, with mapped columns:
    if let authorRow = row.variant(named: "author") {
        authorRow.value(named: "id")    // 10
        authorRow.value(named: "name")  // Melville
    }
}

:bowtie: Tip: now that we have nice "id" and "name" columns, we can leverage RowConvertible types such as Record subclasses. For example, assuming the Book type consumes the "author" variant in its row initializer and builds a Person from it, the same row can be consumed by both the Book and Person types:

for book in Book.fetch(db, sql, adapter: adapter) {
    book.title        // Moby-Dick
    book.author?.name // Melville
}

And Person and Book can still be fetched without row adapters:

let books = Book.fetchAll(db, "SELECT * FROM books")
let persons = Person.fetchAll(db, "SELECT * FROM persons")

You can mix a main adapter with variant adapters:

let sql = "SELECT main.id AS mainID, main.name AS mainName, " +
          "       friend.id AS friendID, friend.name AS friendName, " +
          "FROM persons main " +
          "LEFT JOIN persons friend ON friend.id = main.bestFriendID"

let mainAdapter = ColumnMapping(["id": "mainID", "name": "mainName"])
let bestFriendAdapter = ColumnMapping(["id": "friendID", "name": "friendName"])
let adapter = mainAdapter.adapter(withVariants: ["bestFriend": bestFriendAdapter])

for row in Row.fetch(db, sql, adapter: adapter) {
    // The fetched row, adapted with mainAdapter:
    row.value(named: "id")   // 1
    row.value(named: "name") // Arthur
    
    // The "bestFriend" variant, with bestFriendAdapter:
    if let bestFriendRow = row.variant(named: "bestFriend") {
        bestFriendRow.value(named: "id")    // 2
        bestFriendRow.value(named: "name")  // Barbara
    }
}

// Assuming Person.init(row: row) consumes the "bestFriend" variant:
for person in Person.fetch(db, sql, adapter: adapter) {
    person.name             // Arthur
    person.bestFriend?.name // Barbara
}

For more information about row adapters, see the documentation of:

  • RowAdapter: the protocol that lets you define your custom row adapters
  • ColumnMapping: a row adapter that renames row columns
  • SuffixRowAdapter: a row adapter that hides the first columns of a row
  • VariantRowAdapter: the row adapter that groups several adapters together to define named variants

Raw SQLite Pointers

Not all SQLite APIs are exposed in GRDB.

The Database.sqliteConnection and Statement.sqliteStatement properties provide the raw pointers that are suitable for SQLite C API:

try dbQueue.inDatabase { db in
    // The raw pointer to a database connection:
    let sqliteConnection = db.sqliteConnection

    // The raw pointer to a statement:
    let statement = try db.makeSelectStatement("SELECT ...")
    let sqliteStatement = statement.sqliteStatement
}

☝️ Notes

  • Those pointers are owned by GRDB: don't close connections or finalize statements created by GRDB.
  • SQLite connections are opened in the "multi-thread mode", which (oddly) means that they are not thread-safe. Make sure you touch raw databases and statements inside their dedicated dispatch queues.

Before jumping in the low-level wagon, here is a reminder of most SQLite APIs used by GRDB:

Application Tools

On top of the SQLite API described above, GRDB provides a toolkit for applications. While none of those are mandatory, all of them help dealing with the database:

Records

On top of the SQLite API, GRDB provides protocols and a class that help manipulating database rows as regular objects named "records".

Your custom structs and classes can adopt each protocol individually, and opt in to focused sets of features. Or you can subclass the Record class, and get the full toolkit in one go: fetching methods, persistence methods, and changes tracking.

Inserting Records

To insert a record in the database, subclass the Record class or adopt the Persistable protocol, and call the insert method:

class Person : Record { ... }

let person = Person(name: "Arthur", email: "arthur@example.com")
try person.insert(db)

Of course, you need to open a database connection, and create a database table first.

Fetching Records

Record subclasses and types that adopt the RowConvertible protocol can be fetched from the database:

class Person : Record { ... }
let persons = Person.fetchAll(db, "SELECT ...", arguments: ...)

Add the TableMapping protocol and you can stop writing SQL:

let persons = Person.filter(emailColumn != nil).order(nameColumn).fetchAll(db)
let person = Person.fetchOne(db, key: 1)

To learn more about querying records, check the query interface.

Updating Records

Record subclasses and types that adopt the Persistable protocol can be updated in the database:

let person = Person.fetchOne(db, key: 1)!
person.name = "Arthur"
try person.update(db)

Record subclasses track changes:

let person = Person.fetchOne(db, key: 1)!
person.name = "Arthur"
if person.hasPersistentChangedValues {
    try person.update(db)
}

For batch updates, you have to execute an SQL query:

try db.execute("UPDATE persons SET synchronized = 1")

Deleting Records

Record subclasses and types that adopt the Persistable protocol can be deleted from the database:

let person = Person.fetchOne(db, key: 1)!
try person.delete(db)

For batch deletions, you have to execute an SQL query:

try db.execute("DELETE FROM persons")

Counting Records

Record subclasses and types that adopt the TableMapping protocol can be counted:

let personWithEmailCount = Person.filter(email != nil).fetchCount(db)  // Int

You can now jump to:

RowConvertible Protocol

The RowConvertible protocol grants fetching methods to any type that can be built from a database row:

public protocol RowConvertible {
    /// Row initializer
    init(row: Row)
    
    /// Optional method which gives adopting types an opportunity to complete
    /// their initialization after being fetched. Do not call it directly.
    mutating func awakeFromFetch(row: Row)
}

To use RowConvertible, subclass the Record class, or adopt it explicitely. For example:

struct PointOfInterest {
    var id: Int64?
    var title: String?
    var coordinate: CLLocationCoordinate2D
}

extension PointOfInterest : RowConvertible {
    init(row: Row) {
        id = row.value(named: "id")
        title = row.value(named: "title")
        coordinate = CLLocationCoordinate2DMake(
            row.value(named: "latitude"),
            row.value(named: "longitude"))
    }
}

See column values for more information about the row.value() method.

☝️ Note: for performance reasons, the same row argument to init(row:) is reused during the iteration of a fetch query. If you want to keep the row for later use, make sure to store a copy: self.row = row.copy().

RowConvertible allows adopting types to be fetched from SQL queries:

PointOfInterest.fetch(db, "SELECT ...", arguments:...)    // DatabaseSequence<PointOfInterest>
PointOfInterest.fetchAll(db, "SELECT ...", arguments:...) // [PointOfInterest]
PointOfInterest.fetchOne(db, "SELECT ...", arguments:...) // PointOfInterest?

See fetching methods for information about the fetch, fetchAll and fetchOne methods. See fetching rows for more information about the query arguments.

RowConvertible and Row Adapters

RowConvertible types usually consume rows by column name:

extension PointOfInterest : RowConvertible {
    init(row: Row) {
        id = row.value(named: "id")              // "id"
        title = row.value(named: "title")        // "title"
        coordinate = CLLocationCoordinate2DMake(
            row.value(named: "latitude"),        // "latitude"
            row.value(named: "longitude"))       // "longitude"
    }
}

Occasionnally, you'll want to write a complex SQL query that uses different column names. In this case, row adapters are there to help you mapping raw column names to the names expected by your RowConvertible types.

TableMapping Protocol

Adopt the TableMapping protocol on top of RowConvertible, and you are granted with the full query interface.

public protocol TableMapping {
    static func databaseTableName() -> String
}

To use TableMapping, subclass the Record class, or adopt it explicitely. For example:

extension PointOfInterest : TableMapping {
    static func databaseTableName() -> String {
        return "pointOfInterests"
    }
}

Adopting types can be fetched without SQL, using the query interface:

let paris = PointOfInterest.filter(nameColumn == "Paris").fetchOne(db)

You can also fetch records according to their primary key:

// SELECT * FROM persons WHERE id = 1
Person.fetchOne(db, key: 1)              // Person?

// SELECT * FROM persons WHERE id IN (1, 2, 3)
Person.fetchAll(db, keys: [1, 2, 3])     // [Person]

// SELECT * FROM persons WHERE isoCode = 'FR'
Country.fetchOne(db, key: "FR")          // Country?

// SELECT * FROM countries WHERE isoCode IN ('FR', 'US')
Country.fetchAll(db, keys: ["FR", "US"]) // [Country]

// SELECT * FROM citizenships WHERE personID = 1 AND countryISOCode = 'FR'
Citizenship.fetchOne(db, key: ["personID": 1, "countryISOCode": "FR"]) // Citizenship?

Persistable Protocol

GRDB provides two protocols that let adopting types store themselves in the database:

public protocol MutablePersistable : TableMapping {
    /// The name of the database table (from TableMapping)
    static func databaseTableName() -> String
    
    /// The values persisted in the database
    var persistentDictionary: [String: DatabaseValueConvertible?] { get }
    
    /// Optional method that lets your adopting type store its rowID upon
    /// successful insertion. Don't call it directly: it is called for you.
    mutating func didInsert(with rowID: Int64, for column: String?)
}
public protocol Persistable : MutablePersistable {
    /// Non-mutating version of the optional didInsert(with:for:)
    func didInsert(with rowID: Int64, for column: String?)
}

Yes, two protocols instead of one. Both grant exactly the same advantages. Here is how you pick one or the other:

  • If your type is a struct that mutates on insertion, choose MutablePersistable.

    For example, your table has an INTEGER PRIMARY KEY and you want to store the inserted id on successful insertion. Or your table has a UUID primary key, and you want to automatically generate one on insertion.

  • Otherwise, stick with Persistable. Particularly if your type is a class.

The persistentDictionary property returns a dictionary whose keys are column names, and values any DatabaseValueConvertible value (Bool, Int, String, Date, Swift enums, etc.) See Values for more information.

The optional didInsert method lets the adopting type store its rowID after successful insertion. It is called from a protected dispatch queue, and serialized with all database updates.

To use those protocols, subclass the Record class, or adopt one of them explicitely. For example:

extension PointOfInterest : MutablePersistable {
    
    /// The values persisted in the database
    var persistentDictionary: [String: DatabaseValueConvertible?] {
        return [
            "id": id,
            "title": title,
            "latitude": coordinate.latitude,
            "longitude": coordinate.longitude]
    }
    
    // Update id upon successful insertion:
    mutating func didInsert(with rowID: Int64, for column: String?) {
        id = rowID
    }
}

var paris = PointOfInterest(
    id: nil,
    title: "Paris",
    coordinate: CLLocationCoordinate2DMake(48.8534100, 2.3488000))

try paris.insert(db)
paris.id   // some value

Persistence Methods

Record subclasses and types that adopt Persistable are given default implementations for methods that insert, update, and delete:

try pointOfInterest.insert(db) // INSERT
try pointOfInterest.update(db) // UPDATE
try pointOfInterest.save(db)   // Inserts or updates
try pointOfInterest.delete(db) // DELETE
pointOfInterest.exists(db)     // Bool

  • insert, update, save and delete can throw a DatabaseError whenever an SQLite integrity check fails.

  • update can also throw a PersistenceError of type recordNotFound, should the update fail because there is no matching row in the database.

    When saving an object that may or may not already exist in the database, prefer the save method:

  • save makes sure your values are stored in the database.

    It performs an UPDATE if the record has a non-null primary key, and then, if no row was modified, an INSERT. It directly perfoms an INSERT if the record has no primary key, or a null primary key.

    Despite the fact that it may execute two SQL statements, save behaves as an atomic operation: GRDB won't allow any concurrent thread to sneak in (see concurrency).

  • delete returns whether a database row was deleted or not.

All primary keys are supported, including primary keys that span several columns.

Customizing the Persistence Methods

Your custom type may want to perform extra work when the persistence methods are invoked.

For example, it may want to have its UUID automatically set before inserting. Or it may want to validate its values before saving.

When you subclass Record, you simply have to override the customized method, and call super:

class Person : Record {
    var uuid: String?
    
    override func insert(_ db: Database) throws {
        if uuid == nil {
            uuid = NSUUID().UUIDString
        }
        try super.insert(db)
    }
}

If you use the raw Persistable protocol, use one of the special methods performInsert, performUpdate, performSave, performDelete, or performExists:

struct Link : Persistable {
    var url: URL
    
    func insert(_ db: Database) throws {
        try validate()
        try performInsert(db)
    }
    
    func update(_ db: Database) throws {
        try validate()
        try performUpdate(db)
    }
    
    func validate() throws {
        if url.host == nil {
            throw ValidationError("url must be absolute.")
        }
    }
}

☝️ Note: the special methods performInsert, performUpdate, etc. are reserved for your custom implementations. Do not use them elsewhere. Do not provide another implementation for those methods.

☝️ Note: it is recommended that you do not implement your own version of the save method. Its default implementation forwards the job to update or insert: these are the methods that may need customization, not save.

Record Class

Record is a class that is designed to be subclassed, and provides the full GRDB Record toolkit in one go:

Record subclasses override the four core methods that define their relationship with the database:

class Record {
    /// The table name
    class func databaseTableName() -> String
    
    /// Initialize from a database row
    required init(row: Row)
    
    /// The values persisted in the database
    var persistentDictionary: [String: DatabaseValueConvertible?]
    
    /// Optionally update record ID after a successful insertion
    func didInsert(with rowID: Int64, for column: String?)
}

For example, here is a fully functional Record subclass:

class PointOfInterest : Record {
    var id: Int64?
    var title: String?
    var coordinate: CLLocationCoordinate2D
    
    /// The table name
    override class func databaseTableName() -> String {
        return "pointOfInterests"
    }
    
    /// Initialize from a database row
    required init(row: Row) {
        id = row.value(named: "id")
        title = row.value(named: "title")
        coordinate = CLLocationCoordinate2DMake(
            row.value(named: "latitude"),
            row.value(named: "longitude"))
        super.init(row: row)
    }
    
    /// The values persisted in the database
    override var persistentDictionary: [String: DatabaseValueConvertible?] {
        return [
            "id": id,
            "title": title,
            "latitude": coordinate.latitude,
            "longitude": coordinate.longitude]
    }
    
    /// Update record ID after a successful insertion
    override func didInsert(with rowID: Int64, for column: String?) {
        id = rowID
    }
}

Insert records (see persistence methods):

let poi = PointOfInterest(...)
try poi.insert(db)

Fetch records (see RowConvertible and the query interface):

// Using the query interface
let pois = PointOfInterest.order(titleColumn).fetchAll(db)

// By key
let poi = PointOfInterest.fetchOne(db, key: 1)

// Using SQL
let pois = PointOfInterest.fetchAll(db, "SELECT ...", arguments: ...)

Update records (see persistence methods):

let poi = PointOfInterest.fetchOne(db, key: 1)!
poi.coordinate = ...
try poi.update(db)

Delete records (see persistence methods):

let poi = PointOfInterest.fetchOne(db, key: 1)!
try poi.delete(db)

Changes Tracking

The Record class provides changes tracking.

The update() method always executes an UPDATE statement. When the record has not been edited, this costly database access is generally useless.

Avoid it with the hasPersistentChangedValues property, which returns whether the record has changes that have not been saved:

// Saves the person if it has changes that have not been saved:
if person.hasPersistentChangedValues {
    try person.save(db)
}

The hasPersistentChangedValues flag is false after a record has been fetched or saved into the database. Subsequent modifications may set it, or not: hasPersistentChangedValues is based on value comparison. Setting a property to the same value does not set the changed flag:

let person = Person(name: "Barbara", age: 35)
person.hasPersistentChangedValues // true

try person.insert(db)
person.hasPersistentChangedValues // false

person.name = "Barbara"
person.hasPersistentChangedValues // false

person.age = 36
person.hasPersistentChangedValues // true
person.persistentChangedValues    // ["age": 35]

For an efficient algorithm which synchronizes the content of a database table with a JSON payload, check JSONSynchronization.playground.

The Query Interface

The query interface lets you write pure Swift instead of SQL:

let count = Wine.filter(color == Color.red).fetchCount(db)
let wines = Wine.filter(origin == "Burgundy").order(price).fetchAll(db)

Please bear in mind that the query interface can not generate all possible SQL queries. You may also prefer writing SQL, and this is just OK. From little snippets to full queries, your SQL skills are welcome:

let count = Wine.filter(sql: "color = ?", arguments: [Color.Red]).fetchCount(db)
let wines = Wine.fetchAll(db, "SELECT * FROM wines WHERE origin = ? ORDER BY price", arguments: ["Burgundy"])

So don't miss the SQL API.

Requests

Everything starts from a type that adopts the TableMapping protocol, such as a Record subclass (see Records):

class Person: Record { ... }

Declare the table columns that you want to use for filtering, or sorting:

let idColumn = SQLColumn("id")
let nameColumn = SQLColumn("name")

You can now derive requests with the following methods:

  • all
  • select
  • distinct
  • filter
  • group
  • having
  • order
  • reverse
  • limit

All the methods above return another request, which you can further refine by applying another derivation method.

  • all(): the request for all rows.

    // SELECT * FROM "persons"
Person.all()

  • select(expression, ...) defines the selected columns.

    // SELECT "id", "name" FROM "persons"
Person.select(idColumn, nameColumn)

// SELECT MAX("age") AS "maxAge" FROM "persons"
Person.select(max(ageColumn).aliased("maxAge"))

  • distinct() performs uniquing:

    // SELECT DISTINCT "name" FROM "persons"
Person.select(nameColumn).distinct()

  • filter(expression) applies conditions.

    // SELECT * FROM "persons" WHERE ("id" IN (1, 2, 3))
Person.filter([1,2,3].contains(idColumn))

// SELECT * FROM "persons" WHERE (("name" IS NOT NULL) AND ("height" > 1.75))
Person.filter(nameColumn != nil && heightColumn > 1.75)

  • group(expression, ...) groups rows.

    // SELECT "name", MAX("age") FROM "persons" GROUP BY "name"
Person
    .select(nameColumn, max(ageColumn))
    .group(nameColumn)

  • having(expression) applies conditions on grouped rows.

    // SELECT "name", MAX("age") FROM "persons" GROUP BY "name" HAVING MIN("age") >= 18
Person
    .select(nameColumn, max(ageColumn))
    .group(nameColumn)
    .having(min(ageColumn) >= 18)

  • order(ordering, ...) sorts.

    // SELECT * FROM "persons" ORDER BY "name"
Person.order(nameColumn)

// SELECT * FROM "persons" ORDER BY "score" DESC, "name"
Person.order(scoreColumn.desc, nameColumn)

  • reversed() reverses the eventual orderings.

    // SELECT * FROM "persons" ORDER BY "score" ASC, "name" DESC
Person.order(scoreColumn.desc, nameColumn).reversed()

    If no ordering was specified, the result is ordered by rowID in reverse order.

    // SELECT * FROM "persons" ORDER BY "_rowid_" DESC
Person.all().reversed()

  • limit(limit, offset: offset) limits and pages results.

    // SELECT * FROM "persons" LIMIT 5
Person.limit(5)

// SELECT * FROM "persons" LIMIT 5 OFFSET 10
Person.limit(5, offset: 10)

You can refine requests by chaining those methods:

// SELECT * FROM "persons" WHERE ("email" IS NOT NULL) ORDER BY "name"
Person.order(nameColumn).filter(emailColumn != nil)

The select, group and limit methods ignore and replace previously applied selection, grouping and limits. On the opposite, filter, having, and order methods extend the query:

Person                          // SELECT * FROM "persons"
    .filter(nameColumn != nil)  // WHERE (("name" IS NOT NULL)
    .filter(emailColumn != nil) //        AND ("email IS NOT NULL"))
    .order(nameColumn)          // ORDER BY "name"
    .limit(20, offset: 40)      // - ignored -
    .limit(10)                  // LIMIT 10

Raw SQL snippets are also accepted, with eventual arguments:

// SELECT DATE(creationDate), COUNT(*) FROM "persons" WHERE name = 'Arthur' GROUP BY date(creationDate)
Person
    .select(sql: "DATE(creationDate), COUNT(*)")
    .filter(sql: "name = ?", arguments: ["Arthur"])
    .group(sql: "DATE(creationDate)")

Expressions

Feed requests with SQL expressions built from your Swift code:

SQL Operators

  • =, <>, <, <=, >, >=, IS, IS NOT

    Comparison operators are based on the Swift operators ==, !=, ===, !==, <, <=, >, >=:

    // SELECT * FROM "persons" WHERE ("name" = 'Arthur')
Person.filter(nameColumn == "Arthur")

// SELECT * FROM "persons" WHERE ("name" IS NULL)
Person.filter(nameColumn == nil)

// SELECT * FROM "persons" WHERE ("age" <> 18)
Person.filter(ageColumn != 18)

// SELECT * FROM "persons" WHERE ("age" IS NOT 18)
Person.filter(ageColumn !== 18)

// SELECT * FROM "rectangles" WHERE ("width" < "height")
Rectangle.filter(widthColumn < heightColumn)

    ☝️ Note: SQLite string comparison, by default, is case-sensitive and not Unicode-aware. See string comparison if you need more control.

  • *, /, +, -

    SQLite arithmetic operators are derived from their Swift equivalent:

    // SELECT (("temperature" * 1.8) + 32) AS "farenheit" FROM "persons"
Planet.select((temperatureColumn * 1.8 + 32).aliased("farenheit"))

    ☝️ Note: an expression like nameColumn + "rrr" will be interpreted by SQLite as a numerical addition (with funny results), not as a string concatenation.

  • AND, OR, NOT

    The SQL logical operators are derived from the Swift &&, || and !:

    // SELECT * FROM "persons" WHERE ((NOT "verified") OR ("age" < 18))
Person.filter(!verifiedColumn || ageColumn < 18)

  • BETWEEN, IN, IN (subquery), NOT IN, NOT IN (subquery)

    To check inclusion in a collection, call the contains method on any Swift sequence:

    // SELECT * FROM "persons" WHERE ("id" IN (1, 2, 3))
Person.filter([1, 2, 3].contains(idColumn))

// SELECT * FROM "persons" WHERE ("id" NOT IN (1, 2, 3))
Person.filter(![1, 2, 3].contains(idColumn))

// SELECT * FROM "persons" WHERE ("age" BETWEEN 0 AND 17)
Person.filter((0..<18).contains(ageColumn))

// SELECT * FROM "persons" WHERE ("age" BETWEEN 0 AND 17)
Person.filter((0...17).contains(ageColumn))

// SELECT * FROM "persons" WHERE ("name" BETWEEN 'A' AND 'z')
Person.filter(("A"..."z").contains(nameColumn))

// SELECT * FROM "persons" WHERE (("name" >= 'A') AND ("name" < 'z'))
Person.filter(("A"..<"z").contains(nameColumn))

    ☝️ Note: SQLite string comparison, by default, is case-sensitive and not Unicode-aware. See string comparison if you need more control.

    To check inclusion in a subquery, call the contains method on another request:

    // SELECT * FROM "events"
//  WHERE ("userId" IN (SELECT "id" FROM "persons" WHERE "verified"))
let verifiedUserIds = User.select(idColumn).filter(verifiedColumn)
Event.filter(verifiedUserIds.contains(userIdColumn))

  • EXISTS (subquery), NOT EXISTS (subquery)

    To check is a subquery would return any row, use the exists property on another request:

    // SELECT * FROM "persons"
// WHERE EXISTS (SELECT * FROM "books"
//                WHERE books.ownerId = persons.id)
Person.filter(Book.filter(sql: "books.ownerId = persons.id").exists)

SQL Functions

  • ABS, AVG, COUNT, MAX, MIN, SUM:

    Those are based on the abs, average, count, max, min and sum Swift functions:

    // SELECT MIN("age"), MAX("age") FROM persons
Person.select(min(ageColumn), max(ageColumn))

// SELECT COUNT("name") FROM persons
Person.select(count(nameColumn))

// SELECT COUNT(DISTINCT "name") FROM persons
Person.select(count(distinct: nameColumn))

  • IFNULL

    Use the Swift ?? operator:

    // SELECT IFNULL("name", 'Anonymous') FROM persons
Person.select(nameColumn ?? "Anonymous")

// SELECT IFNULL("name", "email") FROM persons
Person.select(nameColumn ?? emailColumn)

  • LOWER, UPPER

    The query interface does not give access to those SQLite functions. Nothing against them, but they are not unicode aware.

    Instead, GRDB extends SQLite with SQL functions that call the Swift built-in string functions capitalized, lowercased, uppercased, localizedCapitalized, localizedLowercased and localizedUppercased:

    Person.select(nameColumn.uppercased())

    ☝️ Note: When comparing strings, you'd rather use a custom comparison function.

  • Custom SQL functions

    You can apply your own custom SQL functions:

    let f = DatabaseFunction("f", ...)

// SELECT f("name") FROM persons
Person.select(f.apply(nameColumn))

Fetching from Requests

Once you have a request, you can fetch the records at the origin of the request:

// Some request based on `Person`
let request = Person.filter(...)... // FetchRequest<Person>

// Fetch persons:
request.fetch(db)    // DatabaseSequence<Person>
request.fetchAll(db) // [Person]
request.fetchOne(db) // Person?

See fetching methods for information about the fetch, fetchAll and fetchOne methods.

For example:

let allPersons = Person.fetchAll(db)                            // [Person]
let arthur = Person.filter(nameColumn == "Arthur").fetchOne(db) // Person?

When the selected columns don't fit the source type, change your target: any other type that adopts the RowConvertible protocol, plain database rows, and even values:

// Double
let request = Person.select(min(heightColumn))
let minHeight = Double.fetchOne(db, request)

// Row
let request = Person.select(min(heightColumn), max(heightColumn))
let row = Row.fetchOne(db, request)!
let minHeight = row.value(atIndex: 0) as Double?
let maxHeight = row.value(atIndex: 1) as Double?

Fetching By Primary Key

Fetching records according to their primary key is a very common task. It has a shortcut which accepts any single-column primary key:

// SELECT * FROM persons WHERE id = 1
Person.fetchOne(db, key: 1)              // Person?

// SELECT * FROM persons WHERE id IN (1, 2, 3)
Person.fetchAll(db, keys: [1, 2, 3])     // [Person]

// SELECT * FROM persons WHERE isoCode = 'FR'
Country.fetchOne(db, key: "FR")          // Country?

// SELECT * FROM countries WHERE isoCode IN ('FR', 'US')
Country.fetchAll(db, keys: ["FR", "US"]) // [Country]

For multiple-column primary keys, provide a dictionary:

// SELECT * FROM citizenships WHERE personID = 1 AND countryISOCode = 'FR'
Citizenship.fetchOne(db, key: ["personID": 1, "countryISOCode": "FR"]) // Citizenship?

Fetching Aggregated Values

Requests can count. The fetchCount() method returns the number of rows that would be returned by a fetch request:

// SELECT COUNT(*) FROM "persons"
let count = Person.fetchCount(db) // Int

// SELECT COUNT(*) FROM "persons" WHERE "email" IS NOT NULL
let count = Person.filter(emailColumn != nil).fetchCount(db)

// SELECT COUNT(DISTINCT "name") FROM "persons"
let count = Person.select(nameColumn).distinct().fetchCount(db)

// SELECT COUNT(*) FROM (SELECT DISTINCT "name", "age" FROM "persons")
let count = Person.select(nameColumn, ageColumn).distinct().fetchCount(db)

Other aggregated values can also be selected and fetched (see SQL Functions):

let request = Person.select(min(heightColumn))
let minHeight = Double.fetchOne(db, request)

let request = Person.select(min(heightColumn), max(heightColumn))
let row = Row.fetchOne(db, request)!
let minHeight = row.value(atIndex: 0) as Double?
let maxHeight = row.value(atIndex: 1) as Double?

Migrations

Migrations are a convenient way to alter your database schema over time in a consistent and easy way.

Migrations run in order, once and only once. When a user upgrades your application, only non-applied migrations are run.

var migrator = DatabaseMigrator()

// v1.0 database
migrator.registerMigration("createTables") { db in
    try db.execute(
        "CREATE TABLE persons (...); " +
        "CREATE TABLE books (...)")
}

// v2.0 database
migrator.registerMigration("AddBirthDateToPersons") { db in
    try db.execute(
        "ALTER TABLE persons ADD COLUMN birthDate DATE")
}

// Migrations for future versions will be inserted here:
//
// // v3.0 database
// migrator.registerMigration("AddYearAgeToBooks") { db in
//     try db.execute(
//         "ALTER TABLE books ADD COLUMN year INT")
// }

try migrator.migrate(dbQueue) // or migrator.migrate(dbPool)

Each migration runs in a separate transaction. Should one throw an error, its transaction is rollbacked, subsequent migrations do not run, and the error is eventually thrown by migrator.migrate(dbQueue).

The memory of applied migrations is stored in the database itself (in a reserved table).

Advanced Database Schema Changes

SQLite does not support many schema changes, and won't let you drop a table column with "ALTER TABLE ... DROP COLUMN ...", for example.

Yet any kind of schema change is still possible. The SQLite documentation explains in detail how to do so: https://www.sqlite.org/lang_altertable.html#otheralter. This technique requires the temporary disabling of foreign key checks, and is supported by the registerMigrationWithDisabledForeignKeyChecks function:

// Add a NOT NULL constraint on persons.name:
migrator.registerMigrationWithDisabledForeignKeyChecks("AddNotNullCheckOnName") { db in
    try db.execute(
        "CREATE TABLE new_persons (id INTEGER PRIMARY KEY, name TEXT NOT NULL);" +
        "INSERT INTO new_persons SELECT * FROM persons;" +
        "DROP TABLE persons;" +
        "ALTER TABLE new_persons RENAME TO persons;")
}

While your migration code runs with disabled foreign key checks, those are re-enabled and checked at the end of the migration, regardless of eventual errors.

Database Changes Observation

The TransactionObserver protocol lets you observe database changes:

public protocol TransactionObserver : class {
    /// Notifies a database change:
    /// - event.kind (insert, update, or delete)
    /// - event.tableName
    /// - event.rowID
    ///
    /// For performance reasons, the event is only valid for the duration of
    /// this method call. If you need to keep it longer, store a copy:
    /// event.copy().
    func databaseDidChange(with event: DatabaseEvent)
    
    /// An opportunity to rollback pending changes by throwing an error.
    func databaseWillCommit() throws
    
    /// Database changes have been committed.
    func databaseDidCommit(_ db: Database)
    
    /// Database changes have been rollbacked.
    func databaseDidRollback(_ db: Database)
}

To activate a transaction observer, add it to the database queue or pool:

let observer = MyObserver()
dbQueue.add(transactionObserver: observer)

Database holds weak references to its transaction observers: they are not retained, and stop getting notifications after they are deallocated.

Unless specified otherwise (see below), a transaction observer is notified of all database changes: inserts, updates and deletes, including indirect ones triggered by ON DELETE and ON UPDATE actions associated to foreign keys.

Changes are not actually applied until databaseDidCommit is called. On the other side, databaseDidRollback confirms their invalidation:

try dbQueue.inTransaction { db in
    try db.execute("INSERT ...") // 1. didChange
    try db.execute("UPDATE ...") // 2. didChange
    return .commit               // 3. willCommit, 4. didCommit
}

try dbQueue.inTransaction { db in
    try db.execute("INSERT ...") // 1. didChange
    try db.execute("UPDATE ...") // 2. didChange
    return .rollback             // 3. didRollback
}

Database statements that are executed outside of an explicit transaction do not drop off the radar:

try dbQueue.inDatabase { db in
    try db.execute("INSERT ...") // 1. didChange, 2. willCommit, 3. didCommit
    try db.execute("UPDATE ...") // 4. didChange, 5. willCommit, 6. didCommit
}

Changes that are on hold because of a savepoint are only notified after the savepoint has been released. This makes sure that notified events are only events that have an opportunity to be committed:

try dbQueue.inTransaction { db in
    try db.execute("INSERT ...")            // 1. didChange
    
    try db.execute("SAVEPOINT foo")
    try db.execute("UPDATE ...")            // delayed
    try db.execute("UPDATE ...")            // delayed
    try db.execute("RELEASE SAVEPOINT foo") // 2. didChange, 3. didChange
    
    try db.execute("SAVEPOINT foo")
    try db.execute("UPDATE ...")            // not notified
    try db.execute("ROLLBACK TO SAVEPOINT foo")
    
    return .commit                          // 4. willCommit, 5. didCommit
}

Eventual errors thrown from databaseWillCommit are exposed to the application code:

do {
    try dbQueue.inTransaction { db in
        ...
        return .commit           // 1. willCommit (throws), 2. didRollback
    }
} catch {
    // 3. The error thrown by the transaction observer.
}

☝️ Note: all callbacks are called in a protected dispatch queue, and serialized with all database updates.

☝️ Note: the databaseDidChange(with:) and databaseWillCommit() callbacks must not touch the SQLite database. This limitation does not apply to databaseDidCommit and databaseDidRollback which can use their database argument.

FetchedRecordsController is based on the TransactionObserver protocol.

See also TableChangeObserver.swift, which shows a transaction observer that notifies of modified database tables with NSNotificationCenter.

Filtering Database Events

Transaction observers can avoid being notified of some database changes they are not interested in.

At first sight, this looks somewhat redundant with the checks that observers can perform in their databaseDidChange method. But the code below is inefficient:

// BAD: An inefficient way to track the "persons" table:
class PersonObserver: TransactionObserverType {
    func databaseDidChange(with event: DatabaseEvent) {
        guard event.tableName == "persons" else {
            return
        }
        // Process change to the "persons" table
    }
}

The databaseDidChange method is invoked for each insertion, deletion, and update of individual rows. When there are many changed rows, the observer will spend of a lot of time performing the same check again and again.

More, when you're interested in specific table columns, you're out of luck, because databaseDidChange does not know about columns: it just knows that a row has been inserted, deleted, or updated, without further detail.

Instead, provide an event filter to the add(transactionObserver:) method, as below:

// This observer will only be notified of changes to the "name" column
// of the "persons" table.
dbQueue.add(transactionObserver: observer, forDatabaseEvents: { event in
    switch event {
    case .Insert(let tableName):
        return tableName == "persons"
    case .Delete(let tableName):
        return tableName == "persons"
    case .Update(let tableName, let columnNames):
        return tableName == "persons" && columnNames.contains("name")
    }
})

This technique is much more efficient, because GRDB will apply the filter only once for each update statement, instead of once for each modified row.

☝️ Note: avoid referring to the observer itself in the event filter closure, because the database would then keep a strong reference to the observer - this is usually undesired.

Support for SQLite Pre-Update Hooks

A custom SQLite build can activate SQLite "preupdate hooks". In this case, TransactionObserverType gets an extra callback which lets you observe individual column values in the rows modified by a transaction:

public protocol TransactionObserverType : class {
    #if SQLITE_ENABLE_PREUPDATE_HOOK
    /// Notifies before a database change (insert, update, or delete)
    /// with change information (initial / final values for the row's
    /// columns).
    ///
    /// The event is only valid for the duration of this method call. If you
    /// need to keep it longer, store a copy: event.copy().
    func databaseWillChange(with event: DatabasePreUpdateEvent)
    #endif
}

FetchedRecordsController

You use FetchedRecordsController to track changes in the results of an SQLite request.

On iOS, FetchedRecordsController can feed a UITableView, and animate rows when the results of the request change.

It looks and behaves very much like Core Data's NSFetchedResultsController.

Given a fetch request, and a type that adopts the RowConvertible protocol, such as a subclass of the Record class, a FetchedRecordsController is able to track changes in the results of the fetch request, and notify of those changes.

On iOS, FetchedRecordsController is able to return the results of the request in a form that is suitable for a UITableView, with one table view row per fetched record.

See GRDBDemoiOS for an sample app that uses FetchedRecordsController.

Creating the Fetched Records Controller

When you initialize a fetched records controller, you provide the following mandatory information:

class Person : Record { ... }
let dbQueue = DatabaseQueue(...)    // Or DatabasePool

// Using a FetchRequest from the Query Interface:
let controller = FetchedRecordsController<Person>(
    dbQueue,
    request: Person.order(SQLColumn("name")))

// Using SQL, and eventual arguments:
let controller = FetchedRecordsController<Person>(
    dbQueue,
    sql: "SELECT * FROM persons ORDER BY name WHERE countryIsoCode = ?",
    arguments: ["FR"])

The fetch request can involve several database tables:

let controller = FetchedRecordsController<Person>(
    dbQueue,
    sql: "SELECT persons.*, COUNT(books.id) AS bookCount " +
         "FROM persons " +
         "LEFT JOIN books ON books.authorId = persons.id " +
         "GROUP BY persons.id " +
         "ORDER BY persons.name")

After creating an instance, you invoke performFetch() to actually execute the fetch.

controller.performFetch()

Responding to Changes

In general, FetchedRecordsController is designed to respond to changes at the database layer, by notifying when database rows change location or values.

Changes are not reflected until they are applied in the database by a successful transaction. Transactions can be explicit, or implicit:

try dbQueue.inTransaction { db in
    try person1.insert(db)
    try person2.insert(db)
    return .commit         // Explicit transaction
}

try dbQueue.inDatabase { db in
    try person1.insert(db) // Implicit transaction
    try person2.insert(db) // Implicit transaction
}

When you apply several changes to the database, you should group them in a single explicit transaction. The controller will then notify of all changes together.

The Changes Notifications

An instance of FetchedRecordsController notifies that the controller’s fetched records have been changed by the mean of callbacks:

controller.trackChanges(
    // controller's records are about to change:
    recordsWillChange: { controller in ... },
    
    // (iOS only) notification of individual record changes:
    tableViewEvent: { (controller, record, event) in ... },
    
    // controller's records have changed:
    recordsDidChange: { controller in ... })

See Implementing Table View Updates for more detail on table view updates on iOS.

All callbacks are optional. When you only need to grab the latest results, you can omit the recordsDidChange argument name:

controller.trackChanges { controller in
    let newPersons = controller.fetchedRecords! // [Person]
}

Callbacks have the fetched record controller itself as an argument: use it in order to avoid memory leaks:

// BAD: memory leak
controller.trackChanges { _ in
    let newPersons = controller.fetchedRecords!
}

// GOOD
controller.trackChanges { controller in
    let newPersons = controller.fetchedRecords!
}

Callbacks are invoked asynchronously. This means that changes made from the main thread are not immediately notified:

// On the main thread
try dbQueue.inDatabase { db in
    try Person(...).insert(db)
}
// Here changes have not yet been notified.

When you need to take immediate action, force the controller to refresh immediately with its performFetch method. In this case, changes callbacks are not called.

Values fetched from inside callbacks may be inconsistent with the controller's records. This is because after database has changed, and before the controller had the opportunity to invoke callbacks in the main thread, other database changes can happen.

To avoid inconsistencies, provide a fetchAlongside argument to the trackChanges method, as below:

controller.trackChanges(
    fetchAlongside: { db in
        // Fetch any extra value, for example the number of fetched records:
        return Person.fetchCount(db)
    },
    recordsDidChange: { (controller, count) in
        // The extra value is the second argument.
        let recordsCount = controller.fetchedRecords!.count
        assert(count == recordsCount) // guaranteed
    })

Modifying the Fetch Request

You can change a fetched records controller's fetch request or SQL query.

The notification callbacks are notified of changes in the fetched records:

controller.setRequest(Person.order(SQLColumn("name")))
controller.setRequest(sql: "SELECT ...", arguments: ...)

☝️ Note: This behavior differs from Core Data's NSFetchedResultsController, which does not notify of record changes when the fetch request is replaced.

Implementing the Table View Datasource Methods

On iOS, the table view data source asks the fetched records controller to provide relevant information:

func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    return fetchedRecordsController.sections.count
}

func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return fetchedRecordsController.sections[section].numberOfRecords
}

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = ...
    let record = fetchedRecordsController.record(at: indexPath)
    // Configure the cell
    return cell
}

☝️ Note: In its current state, FetchedRecordsController does not support grouping table view rows into custom sections: it generates a unique section.

Implementing Table View Updates

On iOS, FetchedRecordsController can notify that the controller’s fetched records have been changed due to some add, remove, move, or update operations, and help your applying the changes in a UITableView.

Record Identity

Updates and moves are nicer to the eye when you perform table view animations. They require the controller to identify individual records in the fetched database rows. You must tell the controller how to do so:

let controller = FetchedRecordsController<Person>(
    dbQueue,
    request: ...,
    isSameRecord: { (person1, person2) in person1.id == person2.id })

When the fetched type adopts the TableMapping protocol, such as Record subclasses, you can use the compareRecordsByPrimaryKey shortcut:

let controller = FetchedRecordsController<Person>(
    dbQueue,
    request: ...,
    compareRecordsByPrimaryKey: true)

Typical Table View Updates

You can use the recordsWillChange and recordsDidChange callbacks to bracket updates to a table view whose content is provided by the fetched records controller, as illustrated in the following example:

// Assume self has a tableView property, and a configureCell(_:atIndexPath:)
// method which updates the contents of a given cell.

self.controller.trackChanges(
    // controller's records are about to change:
    recordsWillChange: { [unowned self] _ in
        self.tableView.beginUpdates()
    },
    
    // notification of individual record changes:
    tableViewEvent: { [unowned self] (controller, record, event) in
        switch event {
        case .insertion(let indexPath):
            self.tableView.insertRows(at: [indexPath], with: .fade)
            
        case .deletion(let indexPath):
            self.tableView.deleteRows(at: [indexPath], with: .fade)
            
        case .update(let indexPath, _):
            if let cell = self.tableView.cellForRow(at: indexPath) {
                self.configure(cell, at: indexPath)
            }
            
        case .move(let indexPath, let newIndexPath, _):
            self.tableView.deleteRows(at: [indexPath], with: .fade)
            self.tableView.insertRows(at: [newIndexPath], with: .fade)

            // // Alternate technique which actually moves cells around:
            // let cell = self.tableView.cellForRow(at: indexPath)
            // self.tableView.moveRow(at: indexPath, to: newIndexPath)
            // if let cell = cell {
            //     self.configure(cell, at: newIndexPath)
            // }
        }
    },
    
    // controller's records have changed:
    recordsDidChange: { [unowned self] _ in
        self.tableView.endUpdates()
    })

See GRDBDemoiOS for an sample app that uses FetchedRecordsController.

☝️ Note: our sample code above uses unowned references to the table view controller. This is a safe pattern as long as the table view controller owns the fetched records controller, and is deallocated from the main thread (this is usually the case). In other situations, prefer weak references.

FetchedRecordsController Concurrency

A fetched records controller can not be used from any thread.

The database itself can be read and modified from any thread, but fetched records controller methods like performFetch or trackChanges are constrained:

By default, they must be used from the main thread. Record changes are also notified on the main thread.

When you create a controller, you can give it a serial dispatch queue. The controller must then be used from this queue, and record changes are notified on this queue as well.

Encryption

GRDB can encrypt your database with SQLCipher.

In the installation phase, use the GRDBCipher framework instead of GRDB. CocoaPods is not supported.

Set the passphrase property of the database configuration before opening your database connection:

import GRDBCipher

var configuration = Configuration()
configuration.passphrase = "secret"
let dbQueue = try DatabaseQueue(path: "...", configuration: configuration)

You can change the passphrase of an encrypted database:

try dbQueue.changePassphrase("newSecret")

Backup

You can backup (copy) a database into another.

Backups can for example help you copying an in-memory database to and from a database file when you implement NSDocument subclasses.

let source: DatabaseQueue = ...      // or DatabasePool
let destination: DatabaseQueue = ... // or DatabasePool
try source.backup(to: destination)

The backup method blocks the current thread until the destination database contains the same contents as the source database.

When the source is a database pool, concurrent writes can happen during the backup. Those writes may, or may not, be reflected in the backup, but they won't trigger any error.

Good To Know

This chapter covers general topics that you should be aware of.

Avoiding SQL Injection

SQL injection is a technique that lets an attacker nuke your database.

XKCD: Exploits of a Mom

https://xkcd.com/327/

Here is an example of code that is vulnerable to SQL injection:

// BAD BAD BAD
let name = textField.text
try dbQueue.inDatabase { db in
    try db.execute("UPDATE students SET name = '\(name)' WHERE id = \(id)")
}

If the user enters a funny string like Robert'; DROP TABLE students; --, SQLite will see the following SQL, and drop your database table instead of updating a name as intended:

UPDATE students SET name = 'Robert';
DROP TABLE students;
--' WHERE id = 1

To avoid those problems, never embed raw values in your SQL queries. The only correct technique is to provide arguments to your SQL queries:

// Good
let name = textField.text
try dbQueue.inDatabase { db in
    try db.execute(
        "UPDATE students SET name = ? WHERE id = ?",
        arguments: [name, id])
}

See Executing Updates for more information on statement arguments.

Error Handling

No SQLite error goes unnoticed.

Some GRDB functions throw a DatabaseError (see the list of SQLite error codes):

do {
    try db.execute(
        "INSERT INTO pets (masterId, name) VALUES (?, ?)",
        arguments: [1, "Bobby"])
} catch let error as DatabaseError {
    // The SQLite error code: 19 (SQLITE_CONSTRAINT)
    error.code
    
    // The eventual SQLite message: FOREIGN KEY constraint failed
    error.message
    
    // The eventual erroneous SQL query
    // "INSERT INTO pets (masterId, name) VALUES (?, ?)"
    error.sql

    // Full error description:
    // "SQLite error 19 with statement `INSERT INTO pets (masterId, name)
    //  VALUES (?, ?)` arguments [1, "Bobby"]: FOREIGN KEY constraint failed""
    error.description
}

Fatal errors uncover programmer errors, false assumptions, and prevent misuses:

// fatal error:
// SQLite error 1 with statement `SELECT * FROM boooks`:
// no such table: boooks
Row.fetchAll(db, "SELECT * FROM boooks")
// solution: fix the SQL query:
Row.fetchAll(db, "SELECT * FROM books")

// fatal error: could not convert NULL to String.
let name: String = row.value(named: "name")
// solution: fix the contents of the database, or load an optional:
let name: String? = row.value(named: "name")

// fatal error: Database methods are not reentrant.
dbQueue.inDatabase { db in
    dbQueue.inDatabase { db in
        ...
    }
}
// solution: avoid reentrancy, and instead pass a database connection along.

Fatal errors can be avoided. For example, let's consider the code below:

// Some untrusted SQL query
let sql = "SELECT ..."

// Some untrusted arguments for the query
let arguments: NSDictionary = ...

for row in Row.fetchAll(db, sql, arguments: StatementArguments(arguments)) {
    // Some untrusted database value:
    let date: Date? = row.value(atIndex: 0)
}

It has several opportunities to throw fatal errors:

  • The sql string may contain invalid sql, or refer to non-existing tables or columns.
  • The dictionary may contain objects that can't be converted to database values.
  • The dictionary may miss values required by the statement.
  • The row may contain a non-null value that can't be turned into a date.

In such a situation where nothing can be trusted, you can still avoid fatal errors, but you have to expose and handle each failure point by going down one level in GRDB API:

// SQL may be invalid
let statement = try db.makeSelectStatement(sql)

// NSDictionary arguments may contain invalid values or keys:
if let arguments = StatementArguments(arguments) {
    
    // Arguments may not fit the statement
    try statement.validate(arguments: arguments)
    
    // OK we can fetch now
    statement.unsafeSetArguments(arguments) // no need to check twice
    for row in Row.fetchAll(statement) {
        
        // Database value may not be convertible to Date
        let dbv = row.databaseValue(atIndex: 0)
        if let date = Date.fromDatabaseValue(dbv) {
            // use date
        }
    }
}

See prepared statements and DatabaseValue for more information.

Unicode

SQLite lets you store unicode strings in the database.

However, SQLite does not provide any unicode-aware string transformations or comparisons.

Unicode functions

The UPPER and LOWER built-in SQLite functions are not unicode-aware:

// "JéRôME"
String.fetchOne(db, "SELECT UPPER('Jérôme')")

GRDB extends SQLite with SQL functions that call the Swift built-in string functions capitalized, lowercased, uppercased, localizedCapitalized, localizedLowercased and localizedUppercased:

// "JÉRÔME"
let uppercase = DatabaseFunction.uppercase
String.fetchOne(db, "SELECT \(uppercased.name)('Jérôme')")

Those unicode-aware string functions are also readily available in the query interface:

Person.select(nameColumn.uppercased)

String Comparison

SQLite compares strings in many occasions: when you sort rows according to a string column, or when you use a comparison operator such as = and <=.

The comparison result comes from a collating function, or collation. SQLite comes with three built-in collations that do not support Unicode.

GRDB comes with five extra collations that leverage unicode-aware comparisons based on the standard Swift String comparison functions and operators:

  • unicodeCompare (uses the built-in <= and == operators)
  • caseInsensitiveCompare
  • localizedCaseInsensitiveCompare
  • localizedCompare
  • localizedStandardCompare

A collation can be applied to a table column. All comparisons involving this column will then automatically trigger the comparison function:

let collation = DatabaseCollation.localizedCaseInsensitiveCompare
try db.execute(
    "CREATE TABLE persons (" +
        "name TEXT COLLATE \(collation.name)" +
    ")")

// Persons are sorted in a localized case insensitive way:
let persons = Person.order(nameColumn).fetchAll(db)

If you can't or don't want to define the comparison behavior of a column, you can still use an explicit collation in SQL requests and in the query interface:

let collation = DatabaseCollation.localizedCaseInsensitiveCompare
let persons = Person.fetchAll(db,
    "SELECT * FROM persons ORDER BY name COLLATE \(collation.name))")
let persons = Person.order(nameColumn.collating(collation)).fetchAll(db)
let persons = Person.filter(uuidColumn.collating("NOCASE") == uuid).fetchAll(db)

You can also define your own collations:

let collation = DatabaseCollation("customCollation") { (lhs, rhs) -> NSComparisonResult in
    // return the comparison of lhs and rhs strings.
}
dbQueue.add(collation: collation) // Or dbPool.add(collation: ...)

Memory Management

You can reclaim memory used by GRDB.

The most obvious way is to release your database queues and pools:

// Eventually release all memory, after all database accesses are completed:
dbQueue = nil
dbPool = nil

Yet both SQLite and GRDB use non-essential memory that help them perform better. You can claim this memory with the releaseMemory method:

// Release as much memory as possible.
dbQueue.releaseMemory()
dbPool.releaseMemory()

This method blocks the current thread until all current database accesses are completed, and the memory collected.

Memory Management on iOS

The iOS operating system likes applications that do not consume much memory.

Database queues and pools can call the releaseMemory method for you, when application receives memory warnings, and when application enters background: call the setupMemoryManagement method after creating the queue or pool instance:

let dbQueue = try DatabaseQueue(...)
dbQueue.setupMemoryManagement(in: UIApplication.sharedApplication())

Concurrency

Concurrency with GRDB is easy: there are two rules to follow.

GRDB ships with support for two concurrency modes:

  • DatabaseQueue opens a single database connection, and serializes all database accesses.
  • DatabasePool manages a pool of several database connections, serializes writes, and allows concurrent reads and writes.

Rule 1: Your application should have a unique instance of DatabaseQueue or DatabasePool connected to a database file. You may experience concurrency trouble if you do otherwise.

Now let's talk about the consistency of your data: you generally want to prevent your application threads from any conflict.

Since it is difficult to synchronize threads, both DatabaseQueue and DatabasePool offer methods that isolate your statements, and guarantee a stable database state regardless of parallel threads:

dbQueue.inDatabase { db in  // or dbPool.read, or dbPool.write
    // Those two values are guaranteed to be equal:
    let count1 = PointOfInterest.fetchCount(db)
    let count2 = PointOfInterest.fetchCount(db)
}

Isolation is only guaranteed inside the closure argument of those methods. Two consecutive calls don't guarantee isolation:

// Those two values may be different because some other thread may have inserted
// or deleted a point of interest between the two statements:
let count1 = dbQueue.inDatabase { db in
    PointOfInterest.fetchCount(db)
}
let count2 = dbQueue.inDatabase { db in
    PointOfInterest.fetchCount(db)
}

Rule 2: Group your related statements within the safe and isolated inDatabase, inTransaction, read, write and writeInTransaction methods.

Advanced Concurrency

SQLite concurrency is a wiiide topic.

First have a detailed look at the full API of DatabaseQueue and DatabasePool. Both adopt the DatabaseReader and DatabaseWriter protocols, so that you can write code that targets both classes.

If the built-in queues and pools do not fit your needs, or if you can not guarantee that a single queue or pool is accessing your database file, you may have a look at:

See also Transactions for more precise handling of transactions, and Configuration for more precise handling of eventual SQLITE_BUSY errors.

FAQ

  • Generic parameter 'T' could not be inferred

    You may get this error when using DatabaseQueue.inDatabase, DatabasePool.read, or DatabasePool.write:

    // Generic parameter 'T' could not be inferred
let x = dbQueue.inDatabase { db in
    let result = String.fetchOne(db, ...)
    return result
}

    This is a Swift compiler issue (see SR-1570).

    The general workaround is to explicitly declare the type of the closure result:

    // General Workaround
let x = dbQueue.inDatabase { db -> String? in
    let result = String.fetchOne(db, ...)
    return result
}

    You can also, when possible, write a single-line closure:

    // Single-line closure workaround:
let x = dbQueue.inDatabase { db in
    String.fetchOne(db, ...)
}

  • How do I close a database connection?

    The short answer is:

    // Eventually close all database connections
dbQueue = nil
dbPool = nil

    You do not explicitely close a database connection: it is managed by a database queue or pool. The connection is closed when all usages of this connection are completed, and when its database queue or pool gets deallocated.

    Database accesses that run in background threads postpone the closing of connections.

    The releaseMemory method of DatabasePool (documentation) will actually close some connections, but the pool will open another connection as soon as you access the database again.

  • How do I open a database stored as a resource of my application?

    If your application does not need to modify the database, open a read-only connection to your resource:

    var configuration = Configuration()
configuration.readonly = true
let dbPath = NSBundle.main().pathForResource("db", ofType: "sqlite")!
let dbQueue = try DatabaseQueue(path: dbPath, configuration: configuration)

    If the application should modify the database, you need to copy it to a place where it can be modified. For example, in the Documents folder. Only then, open a connection:

    let fm = NSFileManager.default()
let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
let dbPath = (documentsPath as NSString).appendingPathComponent("db.sqlite")
if !fm.fileExists(atPath: dbPath) {
    let dbResourcePath = NSBundle.main().pathForResource("db", ofType: "sqlite")!
    try fm.copyItem(atPath: dbResourcePath, toPath: dbPath)
}
let dbQueue = try DatabaseQueue(path: dbPath)

Sample Code

Thanks

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A versatile SQLite toolkit for Swift, with WAL mode support

https://www.sqlite.org

License:MIT License

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