Kotlin¶

Writing the model¶

You can use Kotlin data classes for your entities. Data classes are usually immutable, but you don’t need to declare that explicitly with @PropertyStrategy: the mapper detects that it’s processing Kotlin code, and will assume mutable = false by default:

@Entity
data class Product(@PartitionKey val id: Int?, val description: String?)

Data classes may also be made mutable (by declaring the components with var instead of val). If you choose that approach, you’ll have to annotate your entities with @PropertyStrategy, and also declare a default value for every component in order to generate a no-arg constructor:

@Entity
@PropertyStrategy(mutable = true)
data class Product(@PartitionKey var id: Int? = null, var description: String? = null)

All of the property annotations can be declared directly on the components.

If you want to take advantage of null saving strategies, your components should be nullable.

The other mapper interfaces are direct translations of the Java versions:

@Dao
interface ProductDao {
  @Insert
  fun insert(product: Product)
}

Known limitation: because of a Kotlin bug (KT-4779), you can’t use default interface methods. They will appear as abstract methods to the mapper processor, which will generate an error since they are not properly annotated. As a workaround, you can use a companion object method that takes the DAO as an argument (as shown in UserDao.kt), or query provider methods.

Building¶

<plugin>
  <groupId>org.jetbrains.kotlin</groupId>
  <artifactId>kotlin-maven-plugin</artifactId>
  <version>${kotlin.version}</version>
  <executions>
    <execution>
      <id>kapt</id>
      <goals><goal>kapt</goal></goals>
      <configuration>
        <sourceDirs>
          <sourceDir>src/main/kotlin</sourceDir>
          <sourceDir>src/main/java</sourceDir>
        </sourceDirs>
        <annotationProcessorPaths>
          <annotationProcessorPath>
            <groupId>com.datastax.oss</groupId>
            <artifactId>java-driver-mapper-processor</artifactId>
            <version>${java-driver.version}</version>
          </annotationProcessorPath>
        </annotationProcessorPaths>
      </configuration>
    </execution>
    <execution>
      <id>compile</id>
      <goals><goal>compile</goal></goals>
      ...
    </execution>
  </executions>
</plugin>