Kotlin POJO data model generation tools

Why?

Sharing a huge and complicated set of data model classes (POJOs) across multiple applications can be painful. That set of tools greatly reduces a lot of boilerplate code.

What you need is to describe an interface of data class. Annotation processing will make the rest of it:

• Generate mutable interface;

• Generate default data class implementation;

• Generate DSL function for data class initialization.

How?

Setup Gradle

Don’t forget to add kapt plugin to build.gradle:

plugins {
    id 'kotlin-kapt'
}

Add a custom repository and model dependencies:

repositories {
    mavenCentral()

    maven {
        url 'https://packages.eraga.net/repository/eraga-public-maven-releases/'
    }
}

dependencies {
    compileOnly "net.eraga.tools.model:model-annotations:1.1.0"
    kapt "net.eraga.tools.model:model-processor:1.1.0"
}

Prepare POJOs

Describe your POJO as kotlin interface

@ImplementModel(implSuffix = "Data")
interface Category {
    val id: Int
    val weight: Int
    val name: String
}

Run ./gradlew build and you will get following kapt output in your build/generated folder:

import java.io.Serializable
import kotlin.Int
import kotlin.String
import kotlin.Unit

interface CategoryMutableModel : Category {
    override var id: Int
    override var weight: Int
    override var name: String
}

data class CategoryData(
        override var id: Int = 0,
        override var weight: Int = 0,
        override var name: String = ""
) : CategoryMutableModel, Serializable

fun categoryData(init: CategoryData.() -> Unit): Category {
    val instance = CategoryData()
    instance.init()
    return instance
}

Use it in your project

Using default implementations

Example DSL to create an object of Category type.

val animals = categoryData {
        name = "Animals"
        id = 1
        weight = 10
    }

Using own and default implementations

class OtherCategory(
        override val id: Int,
        override val weight: Int,
        override val name: String,
        var parent: Category) : Category {
}

fun main(args: Array<String>) {
    val animals = categoryData {
        name = "Animals"
        id = 1
        weight = 10
    }

    val otherCategory = OtherCategory(1, 1, "Tigers", parent = animals)
}

Custom default constructor initializers

interface WithAnyId {
    val id: Any
}

interface WithStringId : WithAnyId {
    override val id: String
}

interface WithUUId : WithAnyId {
    @ConstructorInitializer(value = "UUID.randomUUID()")
    override val id: UUID

    @ConstructorInitializer(value = "LocalDateTime.now()")
    val dateTime: LocalDateTime

    /**
    * Chosen by fair roll of dice, don't override in implementations
    */
    @PreventOverride
    val randomNumber: Long
    get() = 4
}