Domain Modules

The domain layer represents the core business logic of the application, independent of any framework or UI concerns. It follows clean architecture principles and defines the business rules through models, gateways, and use cases.

Module Overview

Model

Business objects and domain models

Gateway

Repository interfaces and contracts

Use Case

Business logic and application use cases

Model Module

Module: domain:model Package: es.mobiledev.domain.model Defines the core business objects (Business Objects - Bo) used throughout the application.

ArticleBo

File: domain/model/src/main/java/es/mobiledev/domain/model/article/ArticleBo.kt:3 Represents an article in the domain layer.

data class ArticleBo(
    val id: Long,
    val title: String,
    val authors: List<AuthorBo>,
    val url: String,
    val imageUrl: String,
    val newsSite: String,
    val summary: String,
    val publishedAt: String,
    val updatedAt: String,
)

Long

required

Unique identifier for the article

title

String

required

Article title

authors

List<AuthorBo>

required

List of article authors with their information

url

String

required

URL to the full article

imageUrl

String

required

URL to the article’s featured image

newsSite

String

required

Source news site name

summary

String

required

Brief summary or excerpt of the article

publishedAt

String

required

ISO 8601 formatted publication timestamp

updatedAt

String

required

ISO 8601 formatted last update timestamp

AuthorBo

File: domain/model/src/main/java/es/mobiledev/domain/model/article/AuthorBo.kt:3 Represents an article author.

data class AuthorBo(
    val name: String,
    val socials: SocialsBo?,
)

name

String

required

Author’s full name

socials

SocialsBo?

Optional social media links for the author

SocialsBo

Represents social media links.

data class SocialsBo(
    val twitter: String?,
    val linkedin: String?,
    val instagram: String?
)

ArticleResponseBo

Wrapper for paginated article responses.

data class ArticleResponseBo(
    val results: List<ArticleBo>,
    val count: Int,
    val next: String?,
    val previous: String?
)

results

List<ArticleBo>

required

List of articles in the current page

count

Int

required

Total number of articles available

String?

URL for the next page of results, null if last page

String?

URL for the previous page of results, null if first page

The “Bo” suffix stands for “Business Object” and distinguishes domain models from DTOs (Data Transfer Objects) and DBOs (Database Objects).

Gateway Module

Module: domain:gateway Package: es.mobiledev.domain.gateway Defines interfaces (gateways) that describe how the domain layer interacts with external systems. These interfaces are implemented by the data layer.

ArticleGateway

File: domain/gateway/src/main/java/es/mobiledev/domain/gateway/article/ArticleGateway.kt:7 Interface defining operations for article data access.

interface ArticleGateway {
    suspend fun getArticles(
        limit: Long,
        offset: Long,
    ): Flow<ArticleResponseBo>

    suspend fun getArticleById(
        id: Long
    ): Flow<ArticleBo>

    suspend fun getFavoriteArticles(): Flow<List<ArticleBo>>

    suspend fun saveFavoriteArticle(articleBo: ArticleBo)

    suspend fun removeFavoriteArticle(articleBo: ArticleBo)

    suspend fun isArticleFavorite(id: Long): Flow<Boolean>
}

Methods

getArticles

suspend function

Retrieves a paginated list of articles

limit

Long

required

Maximum number of articles to return

offset

Long

required

Number of articles to skip for pagination

Returns: Flow<ArticleResponseBo> - Flow emitting article response with pagination info

getArticleById

suspend function

Retrieves a single article by its ID

Long

required

Unique article identifier

Returns: Flow<ArticleBo> - Flow emitting the requested article

getFavoriteArticles

suspend function

Retrieves all articles marked as favorites by the userReturns: Flow<List<ArticleBo>> - Flow emitting list of favorite articles

saveFavoriteArticle

suspend function

Adds an article to the user’s favorites

articleBo

ArticleBo

required

Article to mark as favorite

removeFavoriteArticle

suspend function

Removes an article from the user’s favorites

articleBo

ArticleBo

required

Article to remove from favorites

isArticleFavorite

suspend function

Checks if an article is in the user’s favorites

Long

required

Article identifier to check

Returns: Flow<Boolean> - Flow emitting true if article is favorited

PreferencesGateway

Package: es.mobiledev.domain.gateway.preferences Interface for user preferences and app settings.

interface PreferencesGateway {
    suspend fun saveLastOpenTime(timeInMillis: Long)
    suspend fun getLastOpenTime(): Long
}

Gateways follow the Gateway pattern (similar to Repository pattern) and define the contract between domain and data layers. This enables dependency inversion and makes the domain layer testable.

UseCase Module

Module: domain:useCase Package: es.mobiledev.domain.usecase Encapsulates specific business logic operations. Each use case represents a single business action.

GetArticlesUseCase

File: domain/useCase/src/main/java/es/mobiledev/domain/usecase/article/GetArticlesUseCase.kt:7 Retrieves a paginated list of articles.

interface GetArticlesUseCase {
    suspend operator fun invoke(
        limit: Long,
        offset: Long
    ): Flow<ArticleResponseBo>
}

class GetArticlesUseCaseImpl(
    private val articleGateway: ArticleGateway,
) : GetArticlesUseCase {
    override suspend fun invoke(
        limit: Long,
        offset: Long
    ): Flow<ArticleResponseBo> = 
        articleGateway.getArticles(limit = limit, offset = offset)
}

limit

Long

required

Maximum number of articles to retrieve

offset

Long

required

Pagination offset

Returns: Flow<ArticleResponseBo>

GetArticleByIdUseCase

File: domain/useCase/src/main/java/es/mobiledev/domain/usecase/article/GetArticleByIdUseCase.kt:7 Retrieves a specific article by ID.

interface GetArticleByIdUseCase {
    suspend operator fun invoke(
        id: Long,
    ): Flow<ArticleBo>
}

class GetArticleByIdUseCaseImpl(
    private val articleGateway: ArticleGateway,
) : GetArticleByIdUseCase {
    override suspend fun invoke(
        id: Long,
    ): Flow<ArticleBo> = articleGateway.getArticleById(id = id)
}

Long

required

Unique identifier of the article

Returns: Flow<ArticleBo>

GetFavoriteArticlesUseCase

Retrieves all favorite articles.

interface GetFavoriteArticlesUseCase {
    suspend operator fun invoke(): Flow<List<ArticleBo>>
}

Returns: Flow<List<ArticleBo>>

SaveOrRemoveFavoriteArticleUseCase

Toggles an article’s favorite status.

interface SaveOrRemoveFavoriteArticleUseCase {
    suspend operator fun invoke(
        article: ArticleBo,
        isFavorite: Boolean
    )
}

article

ArticleBo

required

The article to toggle

isFavorite

Boolean

required

Current favorite status (will be toggled)

IsArticleFavoriteUseCase

Checks if an article is favorited.

interface IsArticleFavoriteUseCase {
    suspend operator fun invoke(id: Long): Flow<Boolean>
}

Long

required

Article identifier to check

Returns: Flow<Boolean>

Preferences Use Cases

interface GetLastOpenTimeUseCase {
    suspend operator fun invoke(): Long
}

Use Case Pattern

Interface
Implementation
Usage

interface GetArticlesUseCase {
    suspend operator fun invoke(
        limit: Long,
        offset: Long
    ): Flow<ArticleResponseBo>
}

class GetArticlesUseCaseImpl(
    private val articleGateway: ArticleGateway,
) : GetArticlesUseCase {
    override suspend fun invoke(
        limit: Long,
        offset: Long
    ): Flow<ArticleResponseBo> = 
        articleGateway.getArticles(limit, offset)
}

class HomeViewModel(
    private val getArticles: GetArticlesUseCase
) : BaseViewModel<HomeUiData>() {
    fun loadArticles() {
        viewModelScope.launch {
            getArticles(limit = 20, offset = 0)
                .collect { response ->
                    // Handle articles
                }
        }
    }
}

Use cases implement the operator fun invoke() pattern, allowing them to be called like functions. This provides a clean API: useCase(params) instead of useCase.execute(params).

Dependency Injection

Use cases are provided via Hilt modules:

@Module
@InstallIn(ViewModelComponent::class)
object UseCaseModule {
    @Provides
    fun provideGetArticlesUseCase(
        articleGateway: ArticleGateway
    ): GetArticlesUseCase = GetArticlesUseCaseImpl(articleGateway)
}

Modules

Components

Module Overview

Model

Gateway

Use Case

Model Module

ArticleBo

AuthorBo

SocialsBo

ArticleResponseBo

Gateway Module

ArticleGateway

Methods

PreferencesGateway

UseCase Module

GetArticlesUseCase

GetArticleByIdUseCase

GetFavoriteArticlesUseCase

SaveOrRemoveFavoriteArticleUseCase

IsArticleFavoriteUseCase

Preferences Use Cases

Use Case Pattern

Dependency Injection

Build docs developers (and LLMs) love

Modules

Components

​Module Overview

Model

Gateway

Use Case

​Model Module

​ArticleBo

​AuthorBo

​SocialsBo

​ArticleResponseBo

​Gateway Module

​ArticleGateway

​Methods

​PreferencesGateway

​UseCase Module

​GetArticlesUseCase

​GetArticleByIdUseCase

​GetFavoriteArticlesUseCase

​SaveOrRemoveFavoriteArticleUseCase

​IsArticleFavoriteUseCase

​Preferences Use Cases

​Use Case Pattern

​Dependency Injection

Build docs developers (and LLMs) love

Module Overview

Model Module

ArticleBo

AuthorBo

SocialsBo

ArticleResponseBo

Gateway Module

ArticleGateway

Methods

PreferencesGateway

UseCase Module

GetArticlesUseCase

GetArticleByIdUseCase

GetFavoriteArticlesUseCase

SaveOrRemoveFavoriteArticleUseCase

IsArticleFavoriteUseCase

Preferences Use Cases

Use Case Pattern

Dependency Injection