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mpurland / GRDB.swift

A versatile SQLite toolkit for Swift, with WAL mode support

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GRDB.swift

GRDB.swift is an SQLite toolkit for Swift 2.2.

It ships with an SQL API, protocols that turn your custom types in ORM-like objects, safe concurrent accesses to the database (that's pretty unique), and a Swift query interface which lets SQL-allergic developers avoid their most dreaded language.

And it's well-documented, tested, and fast.

You should give it a try.

March 14, 2016: GRDB.swift 0.52.0 is out (changelog). Follow @groue on Twitter for release announcements and usage tips.

Requirements: iOS 7.0+ / OSX 10.9+, Xcode 7+

Usage

Open a connection to the database:

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

Execute SQL statements:

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

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

Fetch database rows and values:

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

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

Insert and fetch records:

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

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

var berlin = PointOfInterest(
    id: nil,
    title: "Berlin",
    favorite: false,
    coordinate: CLLocationCoordinate2DMake(52.52437, 13.41053))

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

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

Avoid SQL with the query interface:

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

let paris = PointOfInterest.fetchOne(dbQueue, key: 1)                    // PointOfInterest?
let berlin = PointOfInterest.filter(title == "Berlin").fetchOne(dbQueue) // PointOfInterest?
let favoritePois = PointOfInterest                                       // [PointOfInterest]
    .filter(favorite)
    .order(title)
    .fetchAll(dbQueue)

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.

Reference

Getting started

SQLite and SQL

Application tools

Good to know

FAQ

Sample Code

Installation

iOS7

You can use GRDB in a project targetting iOS7. See GRDBDemoiOS7 for more information.

CocoaPods

CocoaPods is a dependency manager for Xcode projects.

To use GRDB with CocoaPods, specify in your Podfile:

source 'https://github.com/CocoaPods/Specs.git'
use_frameworks!

pod 'GRDB.swift', '~> 0.52.0'

Carthage

Carthage is another dependency manager for Xcode projects.

To use GRDB with Carthage, specify in your Cartfile:

github "groue/GRDB.swift" ~> 0.52.0

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.

Database Connections

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

Both grant safe database access from any thread of your application.

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:

  • Only 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.
  • Only database queues can open an in-memory database (without database file).

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.

Execute database updates, and fetch arrays or single values:

try dbQueue.execute("CREATE TABLE pointOfInterests (...)")
try PointOfInterest(...).insert(dbQueue)
let pois = PointOfInterest.fetchAll(dbQueue)
let poi = PointOfInterest.fetchOne(dbQueue, key: 1)

You can group statements in transactions. In a multithreaded application, you can isolate a bunch or related statements from concurrent updates: read Concurrency.

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 = [NSFileProtectionKey: ...]  // Configure database protection

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

See Configuration for more details.

:bowtie: Tip: see DemoApps/GRDBDemoiOS/Database.swift for a sample code that sets up a database queue.

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.

Execute database updates, and fetch arrays or single values:

try dbPool.execute("CREATE TABLE pointOfInterests (...)")
try PointOfInterest(...).insert(dbPool)
let pois = PointOfInterest.fetchAll(dbPool)
let poi = PointOfInterest.fetchOne(dbPool, key: 1)

You can group statements in transactions. In a multithreaded application, you can isolate a bunch or related statements from concurrent updates: read Concurrency.

The total number of concurrent reads is limited. When the maximum number has been reached, a read waits for another read to complete.

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 = [NSFileProtectionKey: ...]  // Configure database protection

let dbPool = try DatabasePool(
    path: "/path/to/database.sqlite",
    configuration: config,
    maximumReaderCount: 10)      // The default is 5

See Configuration for more details.

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

⚠️ Warning: database pools, although well tested, are still experimental. In particular, the best number of concurrent reads is unknown. Please share the results of your experiments!

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.

Once granted with a database connection, you can perform SQL requests:

// Create tables:
try dbQueue.execute("CREATE TABLE wines (...)")

// Insert:
let wineId = try dbQueue.execute("INSERT INTO wines (color, name) VALUES (?, ?)",
    arguments: [Color.Red, "Pomerol"]).insertedRowID
print("Inserted wine id: \(wineId)")
    
// Fetch arrays and single values:
let rows = Row.fetchAll(dbQueue, "SELECT * FROM wines")                 // [Row]
let redWineCount = Int.fetchOne(dbQueue, "SELECT COUNT(*) FROM wines")! // Int

// Iterate sequences:
try dbQueue.inDatabase { db in
    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)
    }
}

Advanced topics:

Executing Updates

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, NSDate, Swift enums, etc.).

After an INSERT statement, you extract the inserted Row ID from the result of the execute method:

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

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

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

Fetch Queries

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

Rows are the raw results of SQL queries:

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)
}

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

let wineCount = Int.fetchOne(db, "SELECT COUNT(*) FROM wines")! // Int
let urls = NSURL.fetchAll(db, "SELECT url FROM wines")          // [NSURL]

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

let wines = Wine.fetchAll(db, "SELECT * FROM wines")            // [Wine]
let anyWine = Wine.fetchOne(db, "SELECT * FROM wines LIMIT 1")  // Wine?

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).

    dbQueue.inDatabase { db in
    for row in Row.fetch(db, "SELECT ...") { ... }
}
dbPool.read { db in
    for row in Row.fetch(db, "SELECT ...") { ... }
}

    Don't modify the database during a sequence iteration:

    try dbQueue.inDatabase { db in
    // 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 fetched and iterated on any thread. It contains copies of database values, and can take a lot of memory.

    Load arrays from database queues, pools, or raw databases connections:

    let persons = Person.fetchAll(dbQueue, "SELECT ...") // DatabaseQueue
let persons = Person.fetchAll(dbPool, "SELECT ...")  // DatabasePool
dbQueue.inDatabase { db in
    let persons = Person.fetchAll(db, "SELECT ...")  // Database
}

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

    Like arrays, you can load single values from database queues, pools, or raw databases connections:

    let count = Int.fetchOne(dbQueue, "SELECT COUNT(*) ...") // DatabaseQueue
let count = Int.fetchOne(dbPool, "SELECT COUNT(*) ...")  // DatabasePool
dbQueue.inDatabase { db in
    let count = Int.fetchOne(db, "SELECT COUNT(*) ...")  // Database
}

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, NSDate, Swift enums, etc.).

☝️ 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(). This does not apply to row arrays, which already contain independent copies of the database rows.

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")

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 dateString: String = row.value(named: "date")       // "2015-09-11 18:14:15.123"
let date: NSDate       = row.value(named: "date")       // NSDate
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?
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:

    • All numeric (integer and real) SQLite values to Swift Int, Int32, Int64, Double and Bool (zero is the only false boolean).
    • Text SQLite values to Swift String.
    • Blob SQLite values to NSData.

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

  • Invalid conversions return nil.

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

    Notably, NULL won't turn to anything:

    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.

  • The convenience conversions of SQLite, such as Blob to String, String to Int, or huge Double values to Int, are not guaranteed to apply. You must not rely on them.

Rows as Dictionaries

Rows can be seen as dictionaries of DatabaseValue, an intermediate type between SQLite and your values:

// Test if the column `date` is present:
if let databaseValue = row["date"] {
    
    // Pick the type you need:
    let dateString: String = databaseValue.value() // "2015-09-11 18:14:15.123"
    let date: NSDate = databaseValue.value()       // NSDate
    self.date = databaseValue.value() // Depends on the type of the property.
    
    // Check for NULL:
    if databaseValue.isNull {
        print("NULL")
    }
    
    // The five SQLite storage classes:
    switch databaseValue.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("NSData: \(data)")
    }
}

You can build rows from scratch using the dictionary and NSDictionary initializers (see Values for more information on supported types):

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

Rows are standard collections:

// the number of columns
row.count

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

Rows 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["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, NSDate, Swift enums, etc.). See Values for more information:

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

Values

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

Values can be used as statement arguments:

let url: NSURL = ...
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: NSURL = row.value(named: "url")
    let verified: Bool = row.value(named: "verified")
}

Values can be directly fetched:

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

Use values in Records:

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

Use values in the query interface:

let url = NSURL(string: "http://example.com")!
let link = Link.filter(Col.url == url).fetchOne(db)

NSData (and Memory Savings)

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

Yet, when extracting NSData 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")     // NSData?
}

☝️ 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: NSData = row.value(named: "data")
    
    // This data is copied:
    if let databaseValue = row["data"] {
        let data: NSData = 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")
}

NSDate and NSDateComponents

NSDate and NSDateComponents 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 NSDate NSDateComponents
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 NSDates 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

NSDate

GRDB stores NSDate 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.

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

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

NSDateComponents

NSDateComponents 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 = NSDateComponents()
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 // NSDateComponents

NSNumber and NSDecimalNumber

While NSNumber deserves no special discussion, NSDecimalNumber does.

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")
let integerAmount = amount
    .decimalNumberByMultiplyingByPowerOf10(2)
    .longLongValue
// INSERT INTO transfers (amount) VALUES (100)
try db.execute("INSERT INTO transfers (amount) VALUES (?)", arguments: [integerAmount])

// Read
let integerAmount = Int64.fetchOne(db, "SELECT SUM(amount) FROM transfers")!
let amount = NSDecimalNumber(longLong: integerAmount)
    .decimalNumberByMultiplyingByPowerOf10(-2)

Swift Enums

Swift enums get full support from GRDB as long as their raw values are supported (Int, Int32, Int64 or String):

enum Color : Int {
    case Red, White, Rose
}

enum Grape : String {
    case Chardonnay, Merlot, Riesling
}

Declare adoption of the DatabaseValueConvertible protocol, and the enum type can be stored and fetched from the database just like other value types:

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")
}

Database values that do not match any enum case are extracted as nil:

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

Transactions

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
}

A ROLLBACK statement is issued if an error is thrown within the transaction block.

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
    }
    ...
}

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:

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, NSDate, Swift enums, etc.)

The databaseValue property returns DatabaseValue, a type that wraps the five types supported by SQLite: NULL, Int64, Double, String and NSData. 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.

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

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.updateStatement(updateSQL)
    
    let selectSQL = "SELECT * FROM persons WHERE name = ?"
    let selectStatement = try db.selectStatement(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:

let changes = try updateStatement.execute()
changes.changedRowCount // The number of rows changed by the statement.
changes.insertedRowID   // For INSERT statements, the inserted Row ID.

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"])

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

Custom SQL Functions

SQLite lets you define SQL functions.

You can for example use the Unicode support of Swift strings, and go beyond the ASCII limitations of the built-in SQLite upper() function:

let unicodeUpper = DatabaseFunction(
    "unicodeUpper",   // 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
        guard let string: String = databaseValues[0].value() else {
            return nil
        }
        return string.uppercaseString
    })
dbQueue.addFunction(unicodeUpper)   // Or dbPool.addFunction(...)

// "JÉRÔME"
String.fetchOne(dbQueue, "SELECT unicodeUpper(?)", arguments: ["Jérôme"])!

// "JéRôME"
String.fetchOne(dbQueue, "SELECT upper(?)", arguments: ["Jérôme"])!

The function argument takes an array of DatabaseValue, and returns any valid value (Bool, Int, String, NSDate, 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: [Double] = databaseValues.flatMap { $0.value() }
    return doubles.reduce(0, combine: +) / Double(doubles.count)
}
dbQueue.addFunction(averageOf)

// 2.0
Double.fetchOne(dbQueue, "SELECT averageOf(1, 2, 3)")!

Functions can throw:

let sqrt = DatabaseFunction("sqrt", argumentCount: 1, pure: true) { (databaseValues: [DatabaseValue]) in
    let dbv = databaseValues[0]
    guard let double: Double = dbv.value() else {
        return nil
    }
    guard double >= 0.0 else {
        throw DatabaseError(message: "Invalid negative value in function sqrt()")
    }
    return sqrt(double)
}
dbQueue.addFunction(sqrt)

// fatal error: SQLite error 1 with statement `SELECT sqrt(-1)`:
// Invalid negative value in function sqrt()
Double.fetchOne(dbQueue, "SELECT sqrt(-1)")

See error handling for more information on database errors.

Use custom functions in the query interface:

// SELECT unicodeUpper("name") AS "uppercaseName" FROM persons
Person.select(unicodeUpper.apply(Col.name).aliased("uppercaseName"))

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:

dbQueue.inDatabase { db in
    let sqliteConnection = db.sqliteConnection
    sqlite3_db_config(sqliteConnection, ...)
    
    let statement = db.selectStatement("SELECT ...")
    let sqliteStatement = statement.sqliteStatement
    sqlite3_step(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 means that they are not thread-safe. Make sure you touch raw databases and statements inside the database queues.

Before jumping in the low-level wagon, here is a reminder of SQLite APIs supported 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(email != nil).order(name).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: Row, database: Database)
}

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.

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 using the query interface:

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

You can also fetch records according to their primary key (see fetching methods):

PointOfInterest.fetch(db, keys: ...)    // DatabaseSequence<PointOfInterest>
PointOfInterest.fetchAll(db, keys: ...) // [PointOfInterest]
PointOfInterest.fetchOne(db, key: ...)  // PointOfInterest?

Any single-column primary key is OK:

// 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]

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 didInsertWithRowID(rowID: Int64, forColumn column: String?)
}
public protocol Persistable : MutablePersistable {
    /// Non-mutating version of the optional didInsertWithRowID(:forColumn:)
    func didInsertWithRowID(rowID: Int64, forColumn 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, NSDate, Swift enums, etc.) See Values for more information.

The didInsertWithRowID method is called in a protected dispatch queue.

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 didInsertWithRowID(rowID: Int64, forColumn 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

  • The argument of persistence methods is any object able to write in a database:

    pointOfInterest.insert(dbQueue) // DatabaseQueue
pointOfInterest.insert(dbPool)  // DatabasePool
dbQueue.inDatabase { db in
    pointOfInterest.insert(db)  // Database
}

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

  • update can also throw a PersistenceError of type NotFound, 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: it performs the UPDATE or INSERT statement that makes sure your values are saved in the database.

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

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: DatabaseWriter) 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: NSURL
    
    func insert(db: DatabaseWriter) throws {
        try validate()
        try performInsert(db)
    }
    
    func update(db: DatabaseWriter) 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 builds on top of the RowConvertible, TableMapping and Persistable protocols, and is designed to be subclassed.

It provides persistence methods, changes tracking, and the query interface.

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 didInsertWithRowID(rowID: Int64, forColumn 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)
    }
    
    /// 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 didInsertWithRowID(rowID: Int64, forColumn 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(title).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: 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 redWineCount = 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:

let redWineCount = Int.fetchOne(db,
    "SELECT COUNT(*) FROM wines WHERE color = ?",
    arguments [Color.Red])!
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 id = SQLColumn("id")
let name = SQLColumn("name")

:bowtie: Tip: you don't want to lock a variable such as name for GRDB's fancy API, do you? My own practice is to declare a dedicated Col struct as below (see example declaration and usage):

struct Col {
   static let id = SQLColumn("id")
   static let name = 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(Col.id, Col.name)

// SELECT UPPER("name") FROM "persons"
Person.select(Col.name.uppercaseString)

// SELECT UPPER("name") AS "uppercaseName" FROM "persons"
Person.select(Col.name.uppercaseString.aliased("uppercaseName"))

  • distinct performs uniquing:

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

  • filter(expression) applies conditions.

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

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

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

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

  • having(expression) applies conditions on grouped rows.

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

  • order(sortDescriptor, ...) sorts.

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

// SELECT * FROM "persons" ORDER BY UPPER("name") DESC, "email" ASC
Person.order(Col.name.uppercaseString.desc, Col.email.asc)

  • reverse() reverses the eventual sort descriptors.

    // SELECT * FROM "persons" ORDER BY "name" DESC
Person.order(Col.name).reverse()

// SELECT * FROM "persons" ORDER BY UPPER("name") ASC, "email" DESC
Person.order(Col.name.uppercaseString.desc, Col.email.asc)reverse()

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

    // SELECT * FROM "persons" ORDER BY "id" DESC
Person.all().reverse()

  • 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, in any order.

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

Raw SQL snippets are also accepted:

// SELECT DATE(creationDate), COUNT(*) FROM "persons" GROUP BY date(creationDate)
Person
    .select(sql: "DATE(creationDate), COUNT(*)")
    .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(Col.name == "Arthur")

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

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

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

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

    ☝️ 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((Col.temperature * 1.8 + 32).aliased("farenheit"))

    ☝️ Note: an expression like Col.name + "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(!Col.verified || Col.age < 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(Col.id))

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

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

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

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

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

    ☝️ 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 verifiedUsers = User.filter(Col.verified)
Event.filter(verifiedUsers.select(Col.id).contains(Col.userId))

  • 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(Col.age), max(Col.age))

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

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

  • IFNULL

    Use the Swift ?? operator:

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

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

  • LOWER, UPPER

    Use the lowercaseString and uppercaseString methods:

    // SELECT * FROM persons WHERE LOWER(name) = 'arthur'
Person.filter(Col.name.lowercaseString == 'arthur)

    ☝️ Note: SQLite support for case translation is limited to ASCII characters. When comparing strings as in the example abobe, you may prefer a custom comparison function. When you actually want to transform strings in an Unicode-aware fashion, use a custom SQL function.

  • Custom SQL functions

    You can apply your own custom SQL functions:

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

// SELECT unicodeUpper("name") AS "uppercaseName" FROM persons
Person.select(unicodeUpper.apply(Col.name).aliased("uppercaseName"))

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(...)...

// 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(Col.name == "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(Col.height))
let minHeight = Double.fetchOne(db, request)!

// Row
let request = Person.select(min(Col.height), max(Col.height))
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]

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(Col.email != nil).fetchCount(db)

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

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

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

let request = Person.select(min(Col.height))
let minHeight = Double.fetchOne(db, request)  // Int?

let request = Person.select(min(Col.height), max(Col.height))
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 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 withDisabledForeignKeyChecks argument:

// Add a NOT NULL constraint on persons.name:
migrator.registerMigration("AddNotNullCheckOnName", withDisabledForeignKeyChecks: true) { 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 TransactionObserverType protocol lets you observe database changes:

public protocol TransactionObserverType : class {
    // Notifies a database change:
    // - event.kind (insert, update, or delete)
    // - event.tableName
    // - event.rowID
    func databaseDidChangeWithEvent(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.addTransactionObserver(observer)

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

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 db.execute("INSERT ...") // 1. didChange, 2. willCommit, 3. didCommit
try db.execute("UPDATE ...") // 4. didChange, 5. willCommit, 6. 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 on a protected dispatch queue.

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

Check TableChangeObserver.swift for a transaction observer that notifies, on the main thread, of modified database tables. Your view controllers can listen to those notifications and update their views accordingly.

Good To Know

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

Error Handling

No SQLite error goes unnoticed.

When an SQLite error happens, some GRDB functions throw a DatabaseError, and some crash with a fatal error:

// fatal error:
// SQLite error 1 with statement `SELECT * FROM bar`: no such table: bar
Row.fetchAll(db, "SELECT * FROM bar")

do {
    try db.execute(
        "INSERT INTO pets (masterId, name) VALUES (?, ?)",
        arguments: [1, "Bobby"])
} catch let error as DatabaseError {
    // SQLite error 19 with statement `INSERT INTO pets (masterId, name)
    // VALUES (?, ?)` arguments [1, "Bobby"]: FOREIGN KEY constraint failed
    error.description
    
    // The SQLite result 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
}

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

let sql = "SELECT ..."
let arguments: NSDictionary = ...
let rows = Row.fetchAll(dbQueue, sql, arguments: StatementArguments(arguments))

It has many opportunities to fail:

  • The sql string may contain invalid sql, or refer to non-existing tables or columns.
  • The arguments NSDictionary may contain unsuitable values.
  • The arguments NSDictionary may miss values required by the statement.

The safe version of the code above goes down a level in GRDB API, in order to expose each failure point:

// Grab a database connection:
try dbQueue.inDatabase { db in
    
    // Dictionary arguments may contain invalid values:
    if let arguments = StatementArguments(arguments) {
        
        // SQL may be invalid
        let statement = try db.selectStatement(sql)
        
        // Arguments may not fit the statement
        try statement.validateArguments(arguments)
        
        // OK now
        let rows = Row.fetchAll(statement, arguments: arguments)
    }
}

See prepared statements 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 SQLite functions are not unicode-aware. See SQL Functions to learn how you can introduce custom string functions.

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. For SQLite, "Jérôme" and "jerome" will never match.

Fortunately, you can define your own collations, based on the rich set of Swift string comparisons:

let collation = DatabaseCollation("localized_case_insensitive") { (lhs, rhs) in
    return (lhs as NSString).localizedCaseInsensitiveCompare(rhs)
}
dbQueue.addCollation(collation) // Or dbPool.addCollation(...)

Once defined, the custom collation can be applied to a table column. All comparisons involving this column will automatically trigger your comparison function:

// Apply the custom collation to the `name` column
try dbQueue.execute(
    "CREATE TABLE persons (" +
        "name TEXT COLLATE localized_case_insensitive" + // The name of the collation
    ")")

// Persons are sorted as expected:
let persons = Person.order(name).fetchAll(dbQueue)

// Matches "Jérôme", "jerome", etc.
let persons = Person.filter(name == "Jérôme").fetchAll(dbQueue)

If you can't or don't want to define the comparison behavior of a column, you can still use an explicit collation on particular requests:

// SELECT * FROM "persons" WHERE ("name" = 'foo' COLLATE NOCASE)
let persons = Person.filter(name.collating("NOCASE") == "foo").fetchAll(db)

// SELECT * FROM "persons" WHERE ("name" = 'Jérôme' COLLATE localized_case_insensitive)
let persons = Person.filter(name.collating(collation) == "Jérôme").fetchAll(db)

See the query interface for more information.

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.

You should call the releaseMemory method when your application receives a memory warning, and when it enters background. Since releaseMemory is blocking, dispatch it to some background queue so that you avoid freezing your user interface.

For example:

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var dbQueue: DatabaseQueue!
    
    func applicationDidReceiveMemoryWarning(application: UIApplication) {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
            self.dbQueue.releaseMemory()
        }
    }
    
    func applicationDidEnterBackground(application: UIApplication) {
        let task = application.beginBackgroundTaskWithExpirationHandler(nil)
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
            self.dbQueue.releaseMemory()
            application.endBackgroundTask(task)
        }
    }
}

Concurrency

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.

A database queue or pool prevents all concurrency troubles, granted there is no other connection to your database.

As a consequence, 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, as thread-safe as DatabaseQueue and DatabasePool are, your multithreaded application should be well aware that two consecutive statements do not operate on a stable database state:

// 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 = PointOfInterest.fetchCount(dbQueueOrPool)
let count2 = PointOfInterest.fetchCount(dbQueueOrPool)

Now it is easy to avoid surprises, and isolate a bunch or related statements together:

Isolation with DatabaseQueue

In a multithreaded application, use inDatabase or inTransaction to isolate consecutive statements, and make sure they are not disturbed by parallel database updates:

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

dbQueue.inDatabase { db in
    // Now this value may be different:
    let count = PointOfInterest.fetchCount(db)
}

// Wrap statements in a transaction:
try dbQueue.inTransaction { db in
    if let paris = PointOfInterest.fetchOne(db, key: parisId) {
        try paris.delete(db)
    }
    return .Commit
}

The inDatabase and inTransaction methods execute their closure argument in a protected dispatch queue, and block the current thread until your database statements are executed. The database accesses are serialized, which means that no two threads can execute such a closure in parallel.

See Transactions for more information.

Isolation with DatabasePool

In a multithreaded application, use read to isolate consecutive fetch statements, and make sure they are not disturbed by parallel database updates:

dbPool.read { db in
    // Those two values are guaranteed to be equal, even if the `wines`
    // tables is concurrently modified between the two requests:
    let count1 = PointOfInterest.fetchCount(db)
    let count2 = PointOfInterest.fetchCount(db)
}

dbPool.read { db in
    // Now this value may be different:
    let count = PointOfInterest.fetchCount(db)
}

read executes its closure argument in a protected dispatch queue, and blocks the current thread until your database statements are executed. Eventual concurrent updates may happen, but they are not visible inside a read closure.

For isolated updates, use write or writeInTransaction. They also execute their closure argument in a protected dispatch queue, and block the current thread until your database statements are executed. The database writes are serialized, which means that no two threads can execute such a closure in parallel:

try dbPool.write { db in
    try country.save(db)
    try poi.save(db)
}

// Wrap statements in a transaction:
try dbPool.writeInTransaction { db in
    if let paris = PointOfInterest.fetchOne(db, key: parisId) {
        try paris.delete(db)
    }
    return .Commit
}

See Transactions for more information.

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.

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

  • 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.mainBundle().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.defaultManager()
let documentsPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0]
let dbPath = (documentsPath as NSString).stringByAppendingPathComponent("db.sqlite")
if !fm.fileExistsAtPath(dbPath) {
    let dbResourcePath = NSBundle.mainBundle().pathForResource("db", ofType: "sqlite")!
    try! fm.copyItemAtPath(dbResourcePath, toPath: dbPath)
}
let dbQueue = DatabaseQueue(path: dbPath)

Sample Code

Thanks

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