Exposed
- Kotlin course
- Advanced
- Lesson 31/83
- 5 min
Learn the JetBrains Exposed ORM.
What is Exposed?
Exposed is JetBrains' SQL ORM library for Kotlin. It declares tables as Kotlin objects and lets you write SQL queries in a type safe way.
You open a connection with Database.connect(url, driver). All work happens inside a transaction { ... } block. Tables are declared with object Users : Table() { ... }. Exposed offers a Kotlin API instead of raw SQL; this gives compile time checks and code completion. In this lesson you will set up the basic connection.
Database connection
To connect to a database with Exposed you call Database.connect(url, driver). The URL and driver are database specific.
Example: Database.connect("jdbc:h2:mem:test", driver = "org.h2.Driver"). H2 in memory is a common choice for testing. PostgreSQL or MySQL use their own driver and URL. The connection is shared by all transaction blocks. Real apps use a connection pool like HikariCP for performance.
Practice Database connection and transaction
Open a connection with Database.connect("jdbc:h2:mem:test", driver = "org.h2.Driver"). Inside a transaction { ... } block, print println("Exposed ready").
Starter code
// Exposed
// write here
import org.jetbrains.exposed.sql.*
import org.jetbrains.exposed.sql.transactions.transaction
fun main() {
}Sample solution
fun main() {
Database.connect("jdbc:h2:mem:test", driver = "org.h2.Driver")
transaction {
println("Exposed ready")
}
}Expected output
Exposed ready
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is Exposed used for?
- Making HTTP requests
- Serializing JSON
- SQL database operations Correct answer
- Drawing UI
Explanation: Exposed is a Kotlin ORM for SQL database operations.
2 Complete the connect call
Database.____("jdbc:h2:mem:test", driver = "org.h2.Driver")Database.connect("jdbc:h2:mem:test", driver = "org.h2.Driver")Explanation: Database.connect opens the connection.
3 Match Exposed parts
| Term | Meaning |
|---|---|
Database.connect |
Connection |
transaction |
Transaction block |
Table |
Table base |
object |
Singleton declaration |