Kapper

Kapper is a code generator for Kotlin that simplifies mapping between data classes.

It was designed to map one class to a interface which has multiple implementations.

Usage

Installation

Add the following to your build.gradle.kts file:

dependencies {  
	implementation("dev.murmurs.kapper:kapper:0.0.1")  
}

Example

Given the following data classes:

  
data class User(  
	val id: Int,  
	val name: String,  
	val email: String,  
	val address: Address,  
)  
  
data class UserDto(  
	val id: Int,  
	val name: String,  
	val email: String,  
)

Kapper can generate a mapper that converts a User to a UserDto:

@Mapper  
interface UserMapper {  
	fun userToDto(user: User): UserDto  
}

The generated mapper will be named UserMapperImpl and will be in the same package as the mapper interface.

Multiple Targets

In ActivityPub, Activity has multiple implementations like Create, Update, Delete, etc. But the properties are the same for all of them.

When mapping from openapi generated single ActivityView classes to Multiple Activity implementations, we can use Kapper to map the properties to an interface:

data class ActivityView (  
	val id: String,  
	val type: String,  
	val actor: String,  
	val `object`: String,  
)  
  
interface Activity {  
	val id: String  
	val type: String  
	val actor: String  
	val `object`: String  
}  
  
data class Create(  
	override val id: String,  
	override val type: String,  
	override val actor: String,  
	override val `object`: String,  
) : Activity  
  
data class Update(  
	override val id: String,  
	override val type: String,  
	override val actor: String,  
	override val `object`: String,  
) : Activity  
  
@Mapper  
interface ActivityMapper {  
	@MultipleTarget(  
		"type",  
		targetTypes = [  
			TargetType(  
				discriminatorValue = "Create",  
				targetType = Create::class  
			),  
			TargetType(  
				discriminatorValue = "Update",  
				targetType = Update::class  
			)  
		]  
	)  
	fun activityViewToActivity(activityView: ActivityView): Activity  
}