Junction

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 known 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"])
data class PlaylistSongXRef(
    val pId: Int,
    val sId: Int
)

data class PlaylistWithSongs(
    @Embedded
    val playlist: Playlist,
    @Relation(
        parentColumns = ["playlistId"],
        entity = Song::class,
        entityColumns = ["songId"],
        associateBy = Junction(
            value = PlaylistSongXRef::class,
            parentColumns = ["pId"],
            entityColumns = ["sId"]
        )
    )
    val songs: List<String>
)

@Dao
interface MusicDao {
    @Query("SELECT * FROM Playlist")
    suspend fun 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<*>, parentColumns: Array<String>, entityColumns: Array<String> )`	Cmn

Public properties
`Array<String>`	`entityColumns` The junction columns that will be used to match against the `Relation.entityColumns`.	Cmn
`Array<String>`	`parentColumns` The junction columns that will be used to match against the `Relation.parentColumns`.	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

Added in 3.0.0-alpha05

Junction(
    value: KClass<*>,
    parentColumns: Array<String> = [],
    entityColumns: Array<String> = []
)

Public properties

entityColumns

Cmn

val entityColumns: Array<String>

The junction columns that will be used to match against the Relation.entityColumns.

If not specified it defaults to Relation.entityColumns.

parentColumns

Cmn

val parentColumns: Array<String>

The junction columns that will be used to match against the Relation.parentColumns.

If not specified it defaults to Relation.parentColumns.

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.