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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" // optional - Paging 3 Integration implementation "androidx.room:room-paging:2.4.0-beta01" }
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@Entity public class User { @PrimaryKey public int uid; @ColumnInfo(name = "first_name") public String firstName; @ColumnInfo(name = "last_name") public String lastName;}
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@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); } -
@Database(entities = {User.class}, version = 1) public abstract class AppDatabase extends RoomDatabase { public abstract UserDao userDao(); }
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each Room entity as a class that is annotated with @Entity
@Entity public class User { @PrimaryKey public int id; public String firstName; public String lastName;}
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@PrimaryKey public int id; -
@Entity(primaryKeys = {"firstName", "lastName"}) public class User { public String firstName; public String lastName; } -
@Entity public class User { @PrimaryKey public int id; public String firstName; public String lastName; @Ignore Bitmap picture; }
or this
@Entity(ignoredColumns = "picture")
public class RemoteUser extends User {
@PrimaryKey
public int id;
public boolean hasVpn;
}
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@Fts4(languageId = "lid") @Entity(tableName = "users") public class User { // ... @ColumnInfo(name = "lid") int languageId; } -
@Entity(indices = {@Index(value = {"first_name", "last_name"}, unique = true)}) public class User { @PrimaryKey public int id; @ColumnInfo(name = "first_name") public String firstName; @ColumnInfo(name = "last_name") public String lastName; @Ignore Bitmap picture; }
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@AutoValue @Entity public abstract class User { // Supported annotations must include `@CopyAnnotations`. @CopyAnnotations @PrimaryKey public abstract long getId(); public abstract String getFirstName(); public abstract String getLastName(); // Room uses this factory method to create User objects. public static User create(long id, String firstName, String lastName) { return new AutoValue_User(id, firstName, lastName); } }
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@Dao public interface UserBookDao { @Query("SELECT user.name AS userName, book.name AS bookName " + "FROM user, book " + "WHERE user.id = book.user_id") public LiveData<List<UserBook>> loadUserAndBookNames(); } public class UserBook { public String userName; public String bookName; } -
@Query( "SELECT * FROM user" + "JOIN book ON user.id = book.user_id" ) public Map<User, List<Book>> loadUserAndBookNames(); -
object that you'd like to decompose into its subfields within a table. You can then query the embedded fields just as you would for other individual columns.
public class Address { public String street; public String state; public String city; @ColumnInfo(name = "post_code") public int postCode; } @Entity public class User { @PrimaryKey public int id; public String firstName; @Embedded public Address address; } -
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First, create a class for each of your two entities. One of the entities must include a variable that is a reference to the primary key of the other entity.
@Entity public class User { @PrimaryKey public long userId; public String name; public int age; } @Entity public class Library { @PrimaryKey public long libraryId; public long userOwnerId; } -
Add the
@Relationannotation to the instance of the child entity, withparentColumnset to the name of the primary key column of the parent entity andentityColumnset to the name of the column of the child entity that references the parent entity's primary key.public class UserAndLibrary { @Embedded public User user; @Relation( parentColumn = "userId", entityColumn = "userOwnerId" ) public Library library;}
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Finally, add a method to the DAO class that returns all instances of the data class that pairs the parent entity and the child entity. This method requires Room to run two queries, so add the @Transaction annotation to this method to ensure that the whole operation is performed atomically.
@Transaction @Query("SELECT * FROM User") public List<UserAndLibrary> getUsersAndLibraries();
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First, create a class for each of your two entities. As in the previous example, the child entity must include a variable that is a reference to the primary key of the parent entity.
@Entity public class User { @PrimaryKey public long userId; public String name; public int age; } @Entity public class Playlist { @PrimaryKey public long playlistId; public long userCreatorId; public String playlistName; } -
Add the
@Relationannotation to the instance of the child entity, withparentColumnset to the name of the primary key column of the parent entity andentityColumnset to the name of the column of the child entity that references the parent entity's primary key.public class UserWithPlaylists { @Embedded public User user; @Relation( parentColumn = "userId", entityColumn = "userCreatorId" ) public List<Playlist> playlists; } -
Finally, add a method to the DAO class that returns all instances of the data class that pairs the parent entity and the child entity.
@Transaction @Query("SELECT * FROM User") public List<UserWithPlaylists> getUsersWithPlaylists();
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public class PlaylistWithSongs { @Embedded public Playlist playlist; @Relation( parentColumn = "playlistId", entityColumn = "songId", associateBy = @Junction(PlaylistSongCrossref.class) ) public List<Song> songs; } public class SongWithPlaylists { @Embedded public Song song; @Relation( parentColumn = "songId", entityColumn = "playlistId", associateBy = @Junction(PlaylistSongCrossref.class) ) public List<Playlist> playlists; }
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@Dao public interface UserDao { @Insert(onConflict = OnConflictStrategy.REPLACE) public void insertUsers(User... users); @Insert public void insertBothUsers(User user1, User user2); @Insert public void insertUsersAndFriends(User user, List<User> friends); } -
@Dao public interface UserDao { @Update public void updateUsers(User... users); } -
@Dao public interface UserDao { @Delete public void deleteUsers(User... users); } -
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@Query("SELECT * FROM user") public User[] loadAllUsers(); -
@Query("SELECT * FROM book " + "INNER JOIN loan ON loan.book_id = book.id " + "INNER JOIN user ON user.id = loan.user_id " + "WHERE user.name LIKE :userName") public List<Book> findBooksBorrowedByNameSync(String userName);
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