Move mapping functions into different packages/classes

[dturner]

See https://github.com/android/architecture-samples/pull/908#discussion_r1127589401

[VaradGupta23]

Problem Mapping functions (e.g., converting TaskEntity ↔ Task ↔ TaskDto) are currently scattered across ViewModels, Repositories, or inlined — leading to:

Harder-to-test code

Tight coupling

Low readability and scalability

Solution: Create a mappers package with clear responsibility Step-by-step Implementation:

1. Create a mappers package In your module (e.g., data, domain, or shared), create a new package:

src/ └── main/ └── java/ └── com/example/app/ ├── data/ │ └── mappers/ └── domain/ 2. Create Mapper Classes a. TaskEntityMapper.kt (for DB ↔ Domain)

package com.example.app.data.mappers

import com.example.app.data.local.TaskEntity import com.example.app.domain.model.Task

object TaskEntityMapper {

fun fromEntity(entity: TaskEntity): Task = Task(
    id = entity.id,
    title = entity.title,
    isCompleted = entity.isCompleted
)

fun toEntity(task: Task): TaskEntity = TaskEntity(
    id = task.id,
    title = task.title,
    isCompleted = task.isCompleted
)

} b. TaskDtoMapper.kt (for API ↔ Domain)

package com.example.app.data.mappers

import com.example.app.data.remote.TaskDto import com.example.app.domain.model.Task

object TaskDtoMapper {

fun fromDto(dto: TaskDto): Task = Task(
    id = dto.id,
    title = dto.title,
    isCompleted = dto.done
)

fun toDto(task: Task): TaskDto = TaskDto(
    id = task.id,
    title = task.title,
    done = task.isCompleted
)

} 3. Use in Repository or ViewModel

val task = TaskEntityMapper.fromEntity(taskEntity) val dto = TaskDtoMapper.toDto(task) Bonus: Unit Tests Write testable code in TaskEntityMapperTest.kt:

@Test fun fromEntity converts correctly() { val entity = TaskEntity("1", "Test", false) val task = TaskEntityMapper.fromEntity(entity)

assertEquals("1", task.id)
assertEquals("Test", task.title)
assertFalse(task.isCompleted)

} Final Folder Structure:

data/ ├── local/ │ └── TaskEntity.kt ├── remote/ │ └── TaskDto.kt ├── mappers/ │ ├── TaskEntityMapper.kt │ └── TaskDtoMapper.kt domain/ └── model/ └── Task.kt