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
  • Use org.seasar.doma.jdbc.Result as the return type of @Delete, @Insert and @Update
  • Use org.seasar.doma.jdbc.BatchResult as the return type of @BatchDelete, @BatchInsert and @BatchUpdate
@Dao(config = AppConfig::class)
interface PersonDao {
  @Sql("""
  select * from person where id = /*id*/0
  """)
  @Select
  fun selectById(id: Int): Person

  @Insert
  fun insert(Person person): Result<Person>
}
val dao: PersonDao = ...
val person = Person(name = Name("Jhon"), address = Address(city = "Tokyo", street = "Yaesu"))
val (newPerson, count) = dao.insert(person)

Kotlin specific Criteria API

Note

Prefer the Kotlin specific Criteria API to DAO interfaces.

Doma provides Kotlin specific Criteria API, KEntityql and KNativeQl DSLs. They are very similar with the Entityql and NativeQl DSLs, which are described in Criteria API. The biggest feature of the KEntityql and KNativeQl DSLs is simplicity.

For example, when you use KEntityql, you have to accept a lambda parameter in a WHERE expression as follows:

val entityql = Entityql(config)
val e = Employee_()

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

The lambda parameter c is a bit annoying. On the other hand, when you use KEntityql, the parameter is gone.

val entityql = KEntityql(config)
val e = Employee_()

val list = entityql
    .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 a lot of sample code here.

The KEntityql and KNativeQl DSLs are included in doma-kotlin.jar. 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:2.42.0")
}

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:2.42.0")
    implementation("org.seasar.doma:doma-kotlin:2.42.0")
}

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