Room 中的复合键关系

Question

我收到一个错误

error: BookGroupEntry has a foreign key (bookGroupParameterId) that references BookGroupParameter (id) but BookGroupParameter does not have a unique index on those columns nor the columns are its primary key. SQLite requires having a unique constraint on referenced parent columns so you must add a unique index to BookGroupParameter that has (id) column(s).

这完全让我难以置信，因为我没有错误报告的情况

我的BookGroupParameter表如下

@Entity(
    tableName = "BookGroupParameters",
    primaryKeys = ["id", "parameterId", "bookGroupId"],
    indices = [Index("id")],
    foreignKeys = [
        ForeignKey(
            entity = Parameter::class,
            parentColumns = arrayOf("id"),
            childColumns = arrayOf("parameterId"),
            onDelete = ForeignKey.CASCADE
        ),

        ForeignKey(
            entity = BookGroup::class,
            parentColumns = arrayOf("id"),
            childColumns = arrayOf("bookGroupId"),
            onDelete = ForeignKey.CASCADE
        )]
)
data class BookGroupParameter(
    @NonNull
    var id: Int,
    val bookGroupId: Int,
    val parameterId: Int
) {
}

这是我的 BookGroupEntry 表

@Entity(
    tableName = "BookGroupEntries",foreignKeys = [
        ForeignKey(
            entity = BookGroupParameter::class,
            parentColumns = arrayOf("id"),
            childColumns = arrayOf("bookGroupParameterId"),
            onDelete = ForeignKey.CASCADE
        )]
)
data class BookGroupEntry(
    @PrimaryKey
    var id: Int,
    var value: String,
    val bookGroupParameterId:Int
)

为什么它告诉我 BookGroupEntry 中的 FK 未定义为 BookGroupParameters 表中的 PK？

Answer 1

对我来说错误信息是有道理的：

• Index("id") 确实不是唯一索引
• “id”列不是 BookGroupParameter 表中的主键（因为它的主键是复合的，如您所写）

要摆脱错误，您可以：

1. 要使表 BookGroupParameter 中的索引唯一：

    indices = [Index("id", unique = true)]

1. 将 BookGroupParameter 的复合主键放入 BookGroupEntry：

@Entity(
    tableName = "BookGroupEntries",foreignKeys = [
        ForeignKey(
            entity = BookGroupParameter::class,
            parentColumns = arrayOf("id","bookGroupId","parameterId"),
            childColumns = arrayOf("bookGroupParameterId","bookGroupParameterBookGroupId","bookGroupParameterParameterId"), // changed
            onDelete = ForeignKey.CASCADE
        )]
)
data class BookGroupEntry(
    @PrimaryKey
    var id: Int,
    var value: String,
    val bookGroupParameterId:Int,
    val bookGroupParameterBookGroupId:Int, // added
    val bookGroupParameterParameterId:Int // added
)