I am trying to achieve the following:

I am working with Android Room.

In code:

@Entity(tableName = "BookReadingSchedule")
data class BookReadingSchedule(
    @PrimaryKey
    @ColumnInfo(name = "schedule_id")
    val id: Long = 0,
    val name: String = ""
)

@Entity(tableName = "Books")
data class Books(
    @PrimaryKey
    @ColumnInfo(name = "book_id")
    val id: Long = 0,
    val title: String = ""
)

@Entity(
    tableName = "BooksToRead"
    foreignKeys = [
        ForeignKey(
            entity = BookReadingSchedule::class,
            parentColumns = ["BookReadingSchedule_id"],
            childColumns = ["to_book_id"],
            onDelete = ForeignKey.CASCADE,
            onUpdate = ForeignKey.CASCADE
        )
    ]
)
data class BooksToRead(
    @PrimaryKey
    @ColumnInfo(name = "id")
    val id: Long = 0,
    val title: String = ""
    @ColumnInfo(name = "to_book_id", index = true)
    val book_id: Long,
)

Trying to create this relationship, but, I am not sure whether this is entirely correct or not. I have worked with LINQ C# in MS, but, never done this much on Android. I am using Kotlin.

Links I checked (before I posted here):

• Room DB three table relationship
• Android Room: One database with multiple tables
• How to join three tables in ROOM
• Android room - 3 one-to-many relationship

EDIT: Idea is that for every schedule, there will be only a handful of books that were select to be included within that schedule.

CodePudding user response：

Your @ColumnInfo(name = "schedule_id") should be parentColum for the corresponding table. So you will need something like this

@Entity(
    tableName = "BooksToRead"
    foreignKeys = [
        ForeignKey(
            entity = BookReadingSchedule::class,
            parentColumns = ["schedule_id"],
            childColumns = ["to_schedule_id"],
            onDelete = ForeignKey.CASCADE,
            onUpdate = ForeignKey.CASCADE
        ),
        ForeignKey(
            entity = Books::class,
            parentColumns = ["book_id"],
            childColumns = ["to_book_id"],
            onDelete = ForeignKey.CASCADE,
            onUpdate = ForeignKey.CASCADE
        )
    ]
)