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Kotlin Engine

This engine generates models in Kotlin code. It relies on the following kotlinx libraries:

  • kotlinx.serialization: for JSON serialization
  • kotlinx.datetime: for date/datetime data types

Getting Started

Once you add a Kotlin engine, you should navigate to the engine config and set a package for the Kotlin models, just like we did in the screenshot below. Of course your package probably won't be io.onegen.models.

Kotlin Config

Gradle Config

Let's take a look at what needs to be configured to get the Kotlin models working in your project.

Add dependencies

As mentioned above, Kotlin engine relies on a few dependencies. Add them to your gradle's dependencies block.

  dependencies {
    // other dependencies in your project

    implementation 'org.jetbrains.kotlinx:kotlinx-datetime:0.4.0'
    implementation 'org.jetbrains.kotlinx:kotlinx-serialization-json:1.4.0'

Add the serialization plugin

Add the following line to your plugins block.

  plugins {
    // other plugins in your project

    id 'org.jetbrains.kotlin.plugin.serialization' version '1.6.10'

Then apply the plugin by adding:

apply plugin: 'kotlinx-serialization'

Important: Make sure to update the versions kotlinx-datetime and kotlinx-serialization versions.

Hello Kotlin Example

We published an example repository where we generated Kotlin models of a simple Notes app. You can see the necessary gradle setup as well as some model code.

Data Types


Since java doesn't support unsigned data types, all unsigned data types are expressed as signed data types.

Design Kotlin
bool Boolean
int Int
int8 Byte
int16 Short
int32 Int
int64 Long
uint UInt
uint8 UByte
uint16 UShort
uint32 UInt
uint64 ULong
float Float
double Double
string String
char Char
byte Byte
bytea ByteArray
date LocalDate
datetime LocalDateTime


Name Kotlin Type
Array List
Map Map

Why is Android Room not supported?

We'd love to support the Room database, but its relationship implementation is quite restrictive. We ultimately decided it was out of our scope, we found a way to support you though.

If your project uses the Room database, there are two ways to integrate OneGen models:

a) Using the @Embedded feature

Create wrapper models and use the @Embedded feature to embed the OneGen models.

b) Using Inheritance

Go to the Kotlin config and in Kotlin's General section, do the following:

  • In Class Type select box, pick Regular
  • Check the Open Class switch
  • Now implement your Room models by inheriting from OneGen models

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