Junction

Added in 2.2.0

Kotlin |Java

@Target(allowedTargets = )
@Retention(value = AnnotationRetention.BINARY)
public annotation Junction

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 {
    val pId: Int,
    val sId: Int
}
public class PlaylistWithSongs {
    @Embedded
    val playlist: Playlist
    @Relation(
            parentColumn = "playlistId",
            entity = Song::class,
            entityColumn = "songId",
            associateBy = Junction(
                    value = PlaylistSongXRef::class,
                    parentColumn = "pId",
                    entityColumn = "sId")
    )
    val songs: List<String>
}

@Dao
public interface MusicDao {
    @Query("SELECT * FROM Playlist")
    val getAllPlaylistsWithSongs(): List<PlaylistWithSongs>
}

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

See also
`Relation`

Summary

Public constructors
`Junction( @NonNull KClass<@NonNull ?> value, @NonNull String parentColumn, @NonNull String entityColumn )`

Public methods
`final @NonNull String`	`getEntityColumn()` The junction column that will be used to match against the `Relation.entityColumn`.
`final @NonNull String`	`getParentColumn()` The junction column that will be used to match against the `Relation.parentColumn`.
`final @NonNull KClass<@NonNull ?>`	`getValue()` An entity or database view to be used as a junction table when fetching the relating entities.

Public constructors

Junction

public Junction(
    @NonNull KClass<@NonNull ?> value,
    @NonNull String parentColumn,
    @NonNull String entityColumn
)

Public methods

getEntityColumn

public final @NonNull String getEntityColumn()

The junction column that will be used to match against the Relation.entityColumn.

If not specified it defaults to Relation.entityColumn.

getParentColumn

public final @NonNull String getParentColumn()

The junction column that will be used to match against the Relation.parentColumn.

If not specified it defaults to Relation.parentColumn.

getValue

public final @NonNull KClass<@NonNull ?> getValue()

An entity or database view to be used as a junction table when fetching the relating entities.

Returns
`@NonNull KClass<@NonNull ?>`	The entity or database view to be used as a junction table.