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/exposed/view#
You can inspect project roadmap to see what's coming next or look into Change log for list of bug fixes and improvements.
Currently supported database dialects:
- PostgreSQL
- MySQL
- MariaDB
- Oracle
- SQLite
- H2
- SQL Server
import org.jetbrains.exposed.sql.*
import org.jetbrains.exposed.sql.transactions.transaction
object Users : Table() {
val id = varchar("id", 10).primaryKey() // Column<String>
val name = varchar("name", length = 50) // Column<String>
val cityId = (integer("city_id") references Cities.id).nullable() // Column<Int?>
}
object Cities : Table() {
val id = integer("id").autoIncrement().primaryKey() // Column<Int>
val name = varchar("name", 50) // Column<String>
}
fun main(args: Array<String>) {
Database.connect("jdbc:h2:mem:test", driver = "org.h2.Driver")
transaction {
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
Cities.insert {
it[name] = "Prague"
}
Users.insert {
it[id] = "andrey"
it[name] = "Andrey"
it[cityId] = saintPetersburgId
}
Users.insert {
it[id] = "sergey"
it[name] = "Sergey"
it[cityId] = munichId
}
Users.insert {
it[id] = "eugene"
it[name] = "Eugene"
it[cityId] = munichId
}
Users.insert {
it[id] = "alex"
it[name] = "Alex"
it[cityId] = null
}
Users.insert {
it[id] = "smth"
it[name] = "Something"
it[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 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_Users 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
import org.jetbrains.exposed.sql.*
import org.jetbrains.exposed.sql.transactions.transaction
import org.jetbrains.exposed.dao.*
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(args: Array<String>) {
Database.connect("jdbc:h2:mem:test", driver = "org.h2.Driver")
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
Find more examples and documentation on the wiki.