Junction

public abstract @interface Junction
implements Annotation

Declares a junction to be used for joining a relationship.

If a Relation should use an associative table (also know as junction table or join table) then you can use this annotation to reference such table. This is useful for fetching many-to-many relations.

 @Entity(primaryKeys = {"pId", "sId"})
 public class PlaylistSongXRef {
     int pId;
     int sId;
 }
 public class PlaylistWithSongs {
     @Embedded
     Playlist playlist;
     @Relation(
             parentColumn = "playlistId",
             entity = Song.class,
             entityColumn = "songId",
             associateBy = @Junction(
                     value = PlaylistSongXRef.class,
                     parentColumn = "pId",
                     entityColumn = "sId")
     )
     List<String> songs;
 }
 @Dao
 public interface MusicDao {
     @Query("SELECT * FROM Playlist")
     List<PlaylistWithSongs> getAllPlaylistsWithSongs();
 }
 

In the above example the many-to-many relationship between Song and Playlist has an associative table defined by the entity PlaylistSongXRef.

Summary

Public methods

public String entityColumn ()

public String parentColumn ()

public Class<?> value ()