你如何在 kotlin 中插入/删除所有表从一对多关系到房间？

Question

I have the following entity:

@Entity(tableName = "match_frames_table")
data class DbFrame(
    @PrimaryKey(autoGenerate = false)
    val frameId: Int
)

And below a data class with reference to 3 other entities, including a nested one, DbBreakWithPots :

data class DbFrameWithScoreAndBreakWithPotsAndBallStack(
    @Embedded val frame: DbFrame,
    @Relation(
        parentColumn = "frameId",
        entityColumn = "frameId",
    )
    val frameScore: List<DbScore>,
    @Relation(
        parentColumn = "frameId",
        entityColumn = "frameId",
        entity = DbBreak::class
    )
    val frameStack: List<DbBreakWithPots>,
    @Relation(
        parentColumn = "frameId",
        entityColumn = "frameId"
    )
    val ballStack: List<DbBall>
)

Where DbBreakWithPots is as follows:

data class DbBreakWithPots(
    @Embedded val matchBreak: DbBreak,
    @Relation(
        parentColumn = "breakId",
        entityColumn = "breakId"
    )
    val matchPots: List<DbPot>
)

In my DAO, I implemented the query method, which works fine:

@Query("SELECT * FROM match_frames_table")
fun getMatchFrames(): LiveData<List<DbFrameWithScoreAndBreakWithPotsAndBallStack>>

However, at the moment I am inserting and deleting from the database manually table by table, but the fact that I have nested relations makes it tricky. Is there a way to simply insert a DbFrame and delete it through one sql request?

Answer 1

Let the CASCADE option of the onUpdate and onDelete actions do the work.

More specially define Foreign Keys in the child entities eg :-

@Entity(
    foreignKeys = [
        ForeignKey(entity = DBIdTotal::class, // Parent Entity
            parentColumns = ["id_DBIdTotal"], // column(s) in the parent
            childColumns = ["ref_DBIdTotal"], // column(s) in this table (the child)
            onDelete = ForeignKey.CASCADE, //<<<<<<<<<< if parent is deleted, the deletion is cascaded to the respective children and they are updated
            onUpdate = ForeignKey.CASCADE //<<<<<<<<<< if parent's referenced column(s) is updated then the updated value is changed in the respective children
        )
    ]
)
data class DBIdOpPedido(
    @PrimaryKey
    val id_DBIdOpPedido: Long,
    val ref_DBIdTotal: Long,
    val op: String
)

You don't have to have both actions coded, you may wish to only use onDelete . You may wish to look at:-

• Foreign Key
• SQLite - Foreign Key Support - ON DELETE and ON UPDATE Actions