Room

Room Overview

• Room is a library used for local caching that makes use of annotations for commonly used persistence code.

• Room functionality is composed of:

  • AppDatabase class extending RoomDatabase(and @Database annotation, which much have an array assigned to entities).

  • DAOs (data access objects) for providing methods that interact with the database.

  • Data entities for each of the database’s tables.

Entities

• Classes with the @Entity annotation will by default have database columns corresponding to their fields.

• @PrimaryKey is used to annotate the field used for unique identification within that table. (can set autoGenerate property for ID values). A pair/set of columns may be used instead, assigned to primaryKeys within the @Entity parenthetical code.

Data Relationships

• To relate two Room entities, either:

  • Write an annotated @Query method to return a mapped set of objects. This approach requires more and more complicated SQL queries.

  • Write a class for data access with the @Dao annotation which gets relevant data from the DB.