Kotlin support

Doma supports Kotlin 1.4.0 or later.

Best practices

Here are some recommended methods, such as defining classes and building them with Kotlin.

Entity classes

  • Define as a plain class

  • Specify a Metamodel annotation to the metamodel element of @Entity

@Entity(metamodel = Metamodel())
class Person : AbstractPerson() {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    var id: Int = -1

    var name: Name? = null

    var age: Int? = -1

    var address: Address? = null

    @Column(name = "DEPARTMENT_ID")
    var departmentId: Int = -1

    @Version
    var version: Int = -1
}

Domain classes

  • Define as a data class

  • Define only one constructor

  • Define only one property whose name is value in the constructor

  • Use val for the property definition

@Domain(valueType = String::class)
data class Name(val value: String)

Embeddable classes

  • Define as a data class

  • Define only one constructor

  • Define properties only in the constructor

  • Use val for the property definitions

@Embeddable
data class Address(val city: String, val street: String)

Dao interfaces

  • Specify a SQL template to @org.seasar.doma.Sql

@Dao
interface PersonDao {
  @Sql("""
  select * from person where id = /*id*/0
  """)
  @Select
  fun selectById(id: Int): Person

  @Insert
  fun insert(person: Person): Int
}

val dao: PersonDao = ...
val person = Person(name = Name("John"), address = Address(city = "Tokyo", street = "Yaesu"))
val count = dao.insert(person)

Kotlin specific Criteria API

Note

Prefer the Kotlin specific Criteria API to DAO interfaces.

Doma provides KQueryDsl, a Criteria API specifically for Kotlin. It is very similar with the QueryDsl, which is described in Unified Criteria API. The biggest feature of the KQueryDsl is simplicity.

val queryDsl = KQueryDsl(config)
val e = Employee_()

val list = queryDsl
    .from(e)
    .where {
        eq(e.departmentId, 2)
        isNotNull(e.managerId)
        or {
            gt(e.salary, Salary("1000"))
            lt(e.salary, Salary("2000"))
        }
    }
    .fetch()

You can see mode sample code here.

The KQueryDsl is included in the doma-kotlin module. Note that you should depend on doma-kotlin instead of doma-core in your build script. You can write build.gradle.kts as follows:

dependencies {
    implementation("org.seasar.doma:doma-kotlin:3.6.0")
}

Code Generation

Use Doma CodeGen Plugin. This plugin support Kotlin code generation.

Using kapt in Gradle

Annotation processors are supported in Kotlin with the kapt compiler plugin.

Add the dependencies using the kapt and implementation configuration in your dependencies block. For example, you can write build.gradle.kts as follows:

dependencies {
    kapt("org.seasar.doma:doma-processor:3.6.0")
    implementation("org.seasar.doma:doma-kotlin:3.6.0")
}

To simplify your build script, we recommend you use the Doma Compile Plugin:

Sample project