Room

What is Room?

It is away to use SQLite local database in android apps to save the data locally.

Setup Room:

Before getting start we need to Setup the room, in build.gradle app file we need to add the following:

dependencies {
    def room_version = "2.3.0"

    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"

    // optional - RxJava2 support for Room
    implementation "androidx.room:room-rxjava2:$room_version"

    // optional - RxJava3 support for Room
    implementation "androidx.room:room-rxjava3:$room_version"

    // optional - Guava support for Room, including Optional and ListenableFuture
    implementation "androidx.room:room-guava:$room_version"

    // optional - Test helpers
    testImplementation "androidx.room:room-testing:$room_version"
}

Components in Room:

1- Database class: Main access point for the underlying connection to your app’s persisted data.

2- Data entities: represent the tables in the DB

3- Data access objects (DAOs): Have method that your user to get, insert, update or delete from the DB.

Example of Data entity:

@Entity
public class User {
    @PrimaryKey
    public int uid;

    @ColumnInfo(name = "first_name")
    public String firstName;

    @ColumnInfo(name = "last_name")
    public String lastName;
}

Example of Data access object (DAO):

@Dao
public interface UserDao {
    @Query("SELECT * FROM user")
    List<User> getAll();

    @Query("SELECT * FROM user WHERE uid IN (:userIds)")
    List<User> loadAllByIds(int[] userIds);

    @Query("SELECT * FROM user WHERE first_name LIKE :first AND " +
           "last_name LIKE :last LIMIT 1")
    User findByName(String first, String last);

    @Insert
    void insertAll(User... users);

    @Delete
    void delete(User user);
}

Defines an AppDatabase class Example:

@Database(entities = {User.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {
    public abstract UserDao userDao();
}

Create an instance of the database Example:

AppDatabase db = Room.databaseBuilder(getApplicationContext(),
        AppDatabase.class, "database-name").build();
        
UserDao userDao = db.userDao();
List<User> users = userDao.getAll();