Junction

Added in 2.2.0

Kotlin |Java

Cmn

@Target(allowedTargets = )
@Retention(value = AnnotationRetention.BINARY)
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(value: KClass<*>, parentColumn: String, entityColumn: String)`	Cmn

Public properties
`String`	`entityColumn` The junction column that will be used to match against the `Relation.entityColumn`.	Cmn
`String`	`parentColumn` The junction column that will be used to match against the `Relation.parentColumn`.	Cmn
`KClass<*>`	`value` An entity or database view to be used as a junction table when fetching the relating entities.	Cmn

Public constructors

Junction

Cmn

Junction(value: KClass<*>, parentColumn: String = "", entityColumn: String = "")

Public properties

entityColumn

Cmn

val entityColumn: String

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

If not specified it defaults to Relation.entityColumn.

parentColumn

Cmn

val parentColumn: String

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

If not specified it defaults to Relation.parentColumn.

value

Cmn

val value: KClass<*>

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

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