data-rules

---

description: "Data Class Implementation Rules for Android Development" globs: "" alwaysApply: true

Data Class Implementation Rules

Overview

This rule defines the implementation guidelines for data classes in the Android project. Follow the comprehensive guidelines from DataRules.md.

Key Rules

Naming Conventions

• File Pattern: {Domain}Data.kt or {Domain}ListData.kt (app model), {Domain}Response.kt (API response model)
• Server fields: snake_case
• Client fields: camelCase
• Boolean flags: prefix with 'is' or 'has'
• YN flags: String type with "Y"/"N"

Gson ignores Kotlin defaults and null-safety

Unless every constructor parameter has a default, Gson creates the object without a constructor: a missing key leaves null in non-null fields and false in Boolean = true, and an explicit JSON null gets through either way. Response models therefore take nullable fields; defaults and required checks belong to a mapper (measured — see DataRules.md).

Required Structure

// API response model
data class ExampleResponse(
    @SerializedName("server_field")
    val clientField: Type?
)

// App model, built by the mapper
@Parcelize
data class ExampleData(
    val clientField: Type
) : Parcelable

fun ExampleResponse.toExampleData() = ExampleData(
    clientField = clientField ?: defaultValue // or requireNotNull(clientField)
)

Mandatory Annotations

• @SerializedName: REQUIRED for all API response fields
• @Parcelize: REQUIRED for Android component data transfer (on the app model)

Field Types

• Response models: every server-supplied field nullable; no Kotlin default values
• App models — required fields: Non-null types, checked with requireNotNull in the mapper
• App models — optional fields: Nullable types
• App models — collections: never null (.orEmpty() in the mapper)

Companion Objects

companion object {
    val EMPTY = DataModel("")
    val MOCK = DataModel("test_data")
}