Customizing Mappings¶

AutoMapper provides powerful annotations to handle mismatches in property names or to provide default values when a source property is missing or null.

Renaming Properties with @PropertyMapping¶

Use the propertyMappings array to map properties that have different names between the source and target. Both from and to parameters are mandatory.

Models:

// Domain
data class User(val id: Long, val fullName: String)

// Data Layer
data class UserEntity(val userId: Long, val name: String)

Mapping Definition:

import io.github.jacksever.automapper.annotation.PropertyMapping

@AutoMapper(
    propertyMappings = [
        PropertyMapping(from = "id", to = "userId"),
        PropertyMapping(from = "fullName", to = "name")
    ]
)
fun userMapper(user: User): UserEntity

This also works for renaming enum constants or sealed class implementations.

Providing Default Values with @DefaultValue¶

Use the defaultValues array to provide a fallback value for a target property. This is useful in two scenarios: 1. The source class does not have a corresponding property. 2. The source property is nullable, but the target property is not.

The processor will generate code that uses the provided value if the source property is missing or null.

Models:

enum class Role { ADMIN, GUEST }

// Domain: nullable address, no role
data class User(val id: Long, val address: String?)

// Data Layer: non-nullable address, has a role
data class UserEntity(val id: Long, val address: String, val role: Role)

Mapping Definition:

import io.github.jacksever.automapper.annotation.DefaultValue

@AutoMapper(
    defaultValues = [
        // Provides a value for 'role' (an enum) which is missing in the source
        DefaultValue(property = "role", value = "Role.GUEST"),
        // Provides a value for 'address' if it's null
        DefaultValue(property = "address", value = "Unknown")
    ]
)
fun userMapper(user: User): UserEntity

The same approach works for sealed class objects. It's best to use the simple class name (e.g., TaskState.Idle), as the processor will automatically add the necessary imports.