Exposed - Kotlin SQL Library
Exposed is a lightweight SQL library written for Kotlin language. It does have two layers of database access: typesafe SQL wrapping DSL and lightweight data access objects.
Exposed is currently available for maven/gradle builds at https://bintray.com/kotlin/exposed (read Getting started for more information)
Find more examples and documentation on the wiki.
You can inspect project roadmap to see what's coming next or look into Change log for list of bug fixes and improvements.
If you have any questions feel free to ask at our #exposed channel on kotlinlang.slack.com.
Dialects
Currently supported database dialects:
- PostgreSQL
- MySQL
- MariaDB
- Oracle
- SQLite
- H2
- SQL Server
SQL DSL sample:
import org.jetbrains.exposed.sql.*
import org.jetbrains.exposed.sql.transactions.transaction
object Users : Table() {
val id = varchar("id", 10) // Column<String>
val name = varchar("name", length = 50) // Column<String>
val cityId = (integer("city_id") references Cities.id).nullable() // Column<Int?>
override val primaryKey = PrimaryKey(id, name = "PK_User_ID") // name is optional here
}
object Cities : Table() {
val id = integer("id").autoIncrement() // Column<Int>
val name = varchar("name", 50) // Column<String>
override val primaryKey = PrimaryKey(id, name = "PK_Cities_ID")
}
fun main() {
Database.connect("jdbc:h2:mem:test", driver = "org.h2.Driver", user = "root", password = "")
transaction {
addLogger(StdOutSqlLogger)
SchemaUtils.create (Cities, Users)
val saintPetersburgId = Cities.insert {
it[name] = "St. Petersburg"
} get Cities.id
val munichId = Cities.insert {
it[name] = "Munich"
} get Cities.id
val pragueId = Cities.insert {
it.update(name, stringLiteral(" Prague ").trim().substring(1, 2))
}[Cities.id]
val pragueName = Cities.select { Cities.id eq pragueId }.single()[Cities.name]
assertEquals(pragueName, "Pr")
Users.insert {
it[id] = "andrey"
it[name] = "Andrey"
it[Users.cityId] = saintPetersburgId
}
Users.insert {
it[id] = "sergey"
it[name] = "Sergey"
it[Users.cityId] = munichId
}
Users.insert {
it[id] = "eugene"
it[name] = "Eugene"
it[Users.cityId] = munichId
}
Users.insert {
it[id] = "alex"
it[name] = "Alex"
it[Users.cityId] = null
}
Users.insert {
it[id] = "smth"
it[name] = "Something"
it[Users.cityId] = null
}
Users.update({ Users.id eq "alex"}) {
it[name] = "Alexey"
}
Users.deleteWhere{ Users.name like "%thing"}
println("All cities:")
for (city in Cities.selectAll()) {
println("${city[Cities.id]}: ${city[Cities.name]}")
}
println("Manual join:")
(Users innerJoin Cities).slice(Users.name, Cities.name).
select {(Users.id.eq("andrey") or Users.name.eq("Sergey")) and
Users.id.eq("sergey") and Users.cityId.eq(Cities.id)}.forEach {
println("${it[Users.name]} lives in ${it[Cities.name]}")
}
println("Join with foreign key:")
(Users innerJoin Cities).slice(Users.name, Users.cityId, Cities.name).
select { Cities.name.eq("St. Petersburg") or Users.cityId.isNull()}.forEach {
if (it[Users.cityId] != null) {
println("${it[Users.name]} lives in ${it[Cities.name]}")
}
else {
println("${it[Users.name]} lives nowhere")
}
}
println("Functions and group by:")
((Cities innerJoin Users).slice(Cities.name, Users.id.count()).selectAll().groupBy(Cities.name)).forEach {
val cityName = it[Cities.name]
val userCount = it[Users.id.count()]
if (userCount > 0) {
println("$userCount user(s) live(s) in $cityName")
} else {
println("Nobody lives in $cityName")
}
}
SchemaUtils.drop (Users, Cities)
}
}
Outputs:
SQL: CREATE TABLE IF NOT EXISTS Cities (id INT AUTO_INCREMENT NOT NULL, name VARCHAR(50) NOT NULL, CONSTRAINT PK_Cities_ID PRIMARY KEY (id))
SQL: CREATE TABLE IF NOT EXISTS Users (id VARCHAR(10) NOT NULL, name VARCHAR(50) NOT NULL, city_id INT NULL, CONSTRAINT PK_User_ID PRIMARY KEY (id))
SQL: ALTER TABLE Users ADD FOREIGN KEY (city_id) REFERENCES Cities(id)
SQL: INSERT INTO Cities (name) VALUES ('St. Petersburg')
SQL: INSERT INTO Cities (name) VALUES ('Munich')
SQL: INSERT INTO Cities (name) VALUES ('Prague')
SQL: INSERT INTO Users (id, name, city_id) VALUES ('andrey', 'Andrey', 1)
SQL: INSERT INTO Users (id, name, city_id) VALUES ('sergey', 'Sergey', 2)
SQL: INSERT INTO Users (id, name, city_id) VALUES ('eugene', 'Eugene', 2)
SQL: INSERT INTO Users (id, name, city_id) VALUES ('alex', 'Alex', NULL)
SQL: INSERT INTO Users (id, name, city_id) VALUES ('smth', 'Something', NULL)
SQL: UPDATE Users SET name='Alexey' WHERE Users.id = 'alex'
SQL: DELETE FROM Users WHERE Users.name LIKE '%thing'
All cities:
SQL: SELECT Cities.id, Cities.name FROM Cities
1: St. Petersburg
2: Munich
3: Prague
Manual join:
SQL: SELECT Users.name, Cities.name FROM Users INNER JOIN Cities ON Cities.id = Users.city_id WHERE ((Users.id = 'andrey') or (Users.name = 'Sergey')) and Users.id = 'sergey' and Users.city_id = Cities.id
Sergey lives in Munich
Join with foreign key:
SQL: SELECT Users.name, Users.city_id, Cities.name FROM Users INNER JOIN Cities ON Cities.id = Users.city_id WHERE (Cities.name = 'St. Petersburg') or (Users.city_id IS NULL)
Andrey lives in St. Petersburg
Functions and group by:
SQL: SELECT Cities.name, COUNT(Users.id) FROM Cities INNER JOIN Users ON Cities.id = Users.city_id GROUP BY Cities.name
1 user(s) live(s) in St. Petersburg
2 user(s) live(s) in Munich
SQL: DROP TABLE Users
SQL: DROP TABLE Cities
DAO sample
import org.jetbrains.exposed.dao.*
import org.jetbrains.exposed.dao.id.EntityID
import org.jetbrains.exposed.dao.id.IntIdTable
import org.jetbrains.exposed.sql.*
import org.jetbrains.exposed.sql.transactions.transaction
object Users : IntIdTable() {
val name = varchar("name", 50).index()
val city = reference("city", Cities)
val age = integer("age")
}
object Cities: IntIdTable() {
val name = varchar("name", 50)
}
class User(id: EntityID<Int>) : IntEntity(id) {
companion object : IntEntityClass<User>(Users)
var name by Users.name
var city by City referencedOn Users.city
var age by Users.age
}
class City(id: EntityID<Int>) : IntEntity(id) {
companion object : IntEntityClass<City>(Cities)
var name by Cities.name
val users by User referrersOn Users.city
}
fun main() {
Database.connect("jdbc:h2:mem:test", driver = "org.h2.Driver", user = "root", password = "")
transaction {
addLogger(StdOutSqlLogger)
SchemaUtils.create (Cities, Users)
val stPete = City.new {
name = "St. Petersburg"
}
val munich = City.new {
name = "Munich"
}
User.new {
name = "a"
city = stPete
age = 5
}
User.new {
name = "b"
city = stPete
age = 27
}
User.new {
name = "c"
city = munich
age = 42
}
println("Cities: ${City.all().joinToString {it.name}}")
println("Users in ${stPete.name}: ${stPete.users.joinToString {it.name}}")
println("Adults: ${User.find { Users.age greaterEq 18 }.joinToString {it.name}}")
}
}Outputs:
SQL: CREATE TABLE IF NOT EXISTS Cities (id INT AUTO_INCREMENT NOT NULL, name VARCHAR(50) NOT NULL, CONSTRAINT pk_Cities PRIMARY KEY (id))
SQL: CREATE TABLE IF NOT EXISTS Users (id INT AUTO_INCREMENT NOT NULL, name VARCHAR(50) NOT NULL, city INT NOT NULL, age INT NOT NULL, CONSTRAINT pk_Users PRIMARY KEY (id))
SQL: CREATE INDEX Users_name ON Users (name)
SQL: ALTER TABLE Users ADD FOREIGN KEY (city) REFERENCES Cities(id)
SQL: INSERT INTO Cities (name) VALUES ('St. Petersburg'),('Munich')
SQL: SELECT Cities.id, Cities.name FROM Cities
Cities: St. Petersburg, Munich
SQL: INSERT INTO Users (name, city, age) VALUES ('a', 1, 5),('b', 1, 27),('c', 2, 42)
SQL: SELECT Users.id, Users.name, Users.city, Users.age FROM Users WHERE Users.city = 1
Users in St. Petersburg: a, b
SQL: SELECT Users.id, Users.name, Users.city, Users.age FROM Users WHERE Users.age >= 18
Adults: b, c