Komapper: Kotlin ORM for JDBC and R2DBC

Komapper is an ORM library for server-side Kotlin.

For more documentation, go to our site:

https://www.komapper.org/docs/ (English version)
https://www.komapper.org/ja/docs/ (Japanese version)

Features

Highlighted

Support for both JDBC and R2DBC
Code generation at compile-time using Kotlin Symbol Processing API
Immutable and composable queries
Support for Kotlin value classes
Easy Spring Boot integration

Experimental

Quarkus integration
Spring Native integration
Transaction management using context receivers

Prerequisite

Kotlin 1.5.31 or later
JRE 11 or later
Gradle 7.2 or later

Supported Databases

Komapper is tested with the following databases:

Database	version	JDBC support	R2DBC support
H2 Database	2.1.212	v	v
MariaDB	10.6.3	v	(not working)
MySQL	8.0.25	v	(not working)
Oracle Database XE	18.4.0	v	v
PostgreSQL	12.9	v	v
SQL Server	2019	v	(unstable)

Supported connectivity types:

JDBC 4.3
R2DBC 0.9.1 and 1.0.0

Installation

Add the following code to the Gradle build script (gradle.build.kts).

plugins {
    kotlin("jvm") version "1.7.10"
    id("com.google.devtools.ksp") version "1.7.10-1.0.6"
}

val komapperVersion = "1.4.0"

dependencies {
    platform("org.komapper:komapper-platform:$komapperVersion").let {
        implementation(it)
        ksp(it)
    }
    implementation("org.komapper:komapper-starter-jdbc")
    implementation("org.komapper:komapper-dialect-h2-jdbc")
    ksp("org.komapper:komapper-processor")
}

Sample code

To get complete code, go to our example repository.

Entity class definition

@KomapperEntity
data class Address(
    @KomapperId @KomapperAutoIncrement @KomapperColumn(name = "ADDRESS_ID")
    val id: Int = 0,
    val street: String,
    @KomapperVersion val version: Int = 0,
    @KomapperCreatedAt val createdAt: LocalDateTime? = null,
    @KomapperUpdatedAt val updatedAt: LocalDateTime? = null,
)

Connecting with JDBC

fun main() {
    // create a Database instance
    val db = JdbcDatabase("jdbc:h2:mem:example;DB_CLOSE_DELAY=-1")

    // get a metamodel
    val a = Meta.address

    // execute simple operations in a transaction
    db.withTransaction {
        // create a schema
        db.runQuery {
            QueryDsl.create(a)
        }

        // INSERT
        val newAddress = db.runQuery {
            QueryDsl.insert(a).single(Address(street = "street A"))
        }

        // SELECT
        val address = db.runQuery {
            QueryDsl.from(a).where { a.id eq newAddress.id }.first()
        }
    }
}

Connecting with R2DBC

suspend fun main() {
    // create a Database instance
    val db = R2dbcDatabase("r2dbc:h2:mem:///example;DB_CLOSE_DELAY=-1")

    // get a metamodel
    val a = Meta.address

    // execute simple operations in a transaction
    db.withTransaction {
        // create a schema
        db.runQuery {
            QueryDsl.create(a)
        }

        // INSERT
        val newAddress = db.runQuery {
            QueryDsl.insert(a).single(Address(street = "street A"))
        }

        // SELECT
        val address = db.runQuery {
            QueryDsl.from(a).where { a.id eq newAddress.id }.first()
        }
    }
}

Design Policy

See DESIGN_DOC for the design policy of this project.

palmseung/komapper