android-room-databaselisted

# Android Room Database ## Core Principles - Room is the local persistence layer, not the domain model layer. - Entities are data-layer types only; never expose them to presentation. - DAOs should be focused and query-driven. - Prefer Room as the single source of truth when offline-first behavior is required. - Keep schema ownership explicit — shared DB code belongs in a core database module when multiple features use it. --- ## Recommended Module Ownership Use a dedicated `:core:database` module when the app has a shared Room database used by multiple features: ```text :core:database -> RoomDatabase, entities, DAOs, migrations, converters :core:data -> shared repository/data-source utilities :feature:<name>:data -> mappers and feature-specific data sources using DAOs ``` If only one feature uses Room and the schema is small, it can stay in that feature's `data` module until reuse justifies extraction. See the **android-module-structure** skill for extraction rules. --- ## Entities Entities model how data is stored locally, not how it is shown or used in domain logic: ```kotlin @Entity(tableName = "notes") data class NoteEntity( @PrimaryKey val id: String, val title: String, val body: String, val updatedAtEpochMillis: Long ) ``` Guidelines: - keep entities flat and storage-oriented - prefer primitive columns over nested object graphs - store foreign keys explicitly - use clear table names - avoid putting comput