What is the Room library?

Room is a persistent library that provides an abstract layer over SQLite to simplify database access on Android. It is part of Architecture Components and offers more compile-time query verification.

Main components of Room:

• Entity: A class representing a table in the database. Annotated with @Entity. Each field in the Entity that should be saved must be either a public field or have a public getter.

  @Entity(tableName = "users")
  data class User(
      @PrimaryKey val id: Int,
      val name: String
  )
  

• DAO (Data Access Object): An interface or abstract class containing methods for interacting with the database (insert, update, delete, queries). Annotated with @Dao.

  @Dao
  interface UserDao {
      @Query("SELECT * FROM users WHERE id = :userId")
      fun getUserById(userId: Int): User?
  
      @Insert(onConflict = OnConflictStrategy.IGNORE)
      suspend fun insertUser(user: User)
  }
  

• Database: An abstract class extending RoomDatabase. It links Entity and DAO, providing access points to DAO. Annotated with @Database.

  @Database(entities = [User::class], version = 1)
  abstract class AppDatabase : RoomDatabase() {
      abstract fun userDao(): UserDao
  }
  

Advantages of Room:

• Compile-time verification: Checks SQL queries during compilation, reducing runtime errors.
• Easier integration with Architecture Components: Easily used with LiveData and Paging Library.
• Reduces boilerplate code: Room generates most of the necessary code for database operations.
• Support for Coroutines and Flow: Convenient integration with modern asynchronous programming approaches.

Room abstracts the details of working with SQLite, offering a safer and more convenient way to interact with a local database.