Kotlin 房间-如何设置可为空的外键

在我的Kotlin Android代码库中，我有以下两个实体

@Entity(
tableName = ModuleConfiguration.tableName,
primaryKeys = [ModuleConfiguration.COL_ID],
foreignKeys = arrayOf(
    ForeignKey(
        entity = Module::class,
        parentColumns = [Module.COL_ID],
        childColumns = [ModuleConfiguration.COL_MODULE_ID],
        onDelete = ForeignKey.CASCADE
    ),
    ForeignKey(
        entity = Group::class,
        parentColumns = [Group.COL_ID],
        childColumns = [ModuleConfiguration.COL_GROUP_ID]
    )
)
)
class ModuleConfiguration(
@ColumnInfo(name = COL_ID)
var id: String = UUID.randomUUID().toString(),

@ColumnInfo(name = COL_TABLE)
var table: String,

@ColumnInfo(name = COL_FIELD_NAME)
var fieldName: String,

@ColumnInfo(name = COL_FIELD_LABEL)
var fieldLabel: String,

@ColumnInfo(name = COL_FIELD_TYPE)
var fieldType: ModuleConfigurationItemType,

@ColumnInfo(name = COL_GROUP_ID)
var groupId: String?,

@ColumnInfo(name = COL_MODULE_ID)
var moduleId: String,

@ColumnInfo(name = COL_POSITION)
var position: Int,

@ColumnInfo(name = COL_VISIBLE)
var visible: Int = 1, //Usually visible

@ColumnInfo(name = COL_READ_ONLY)
var readOnly: Int = 0, //Usually false

@ColumnInfo(name = COL_REQUIRED)
var required: Int = 0, //Usually false

@ColumnInfo(name = COL_CREATED_AT)
var createdAt: Long = CustomDateTimeUtil.getTodayInUTC(),

@ColumnInfo(name = COL_UPDATED_AT)
var updatedAt: Long = CustomDateTimeUtil.getTodayInUTC()
) : Cloneable, Serializable, Parcelable  {

constructor(parcel: Parcel) : this(
    parcel.readString() ?: "",
    parcel.readString() ?: "",
    parcel.readString() ?: "",
    parcel.readString() ?: "",
    fieldType = ModuleConfigurationItemType.valueOf(parcel.readString() ?: FieldType.UNKNOWN.name),
    groupId = parcel.readString(),
    moduleId = parcel.readString() ?: "",
    position = parcel.readInt(),
    visible = parcel.readInt(),
    readOnly = parcel.readInt(),
    required = parcel.readInt(),
    createdAt = parcel.readLong(),
    updatedAt = parcel.readLong()
) {
}

fun getViewType() : ModuleConfigurationItemType {
    return this.fieldType
}

override fun equals(other: Any?): Boolean {
    return super.equals(other)
}

override fun hashCode(): Int {
    return super.hashCode()
}

override fun clone(): Any {
    return super.clone()
}

override fun writeToParcel(parcel: Parcel, flags: Int) {
    parcel.writeString(id)
    parcel.writeString(table)
    parcel.writeString(fieldName)
    parcel.writeString(fieldLabel)
    parcel.writeString(fieldType.name)
    parcel.writeString(groupId)
    parcel.writeString(moduleId)
    parcel.writeInt(position)
    parcel.writeInt(visible)
    parcel.writeInt(readOnly)
    parcel.writeInt(required)
    parcel.writeLong(createdAt)
    parcel.writeLong(updatedAt)
}

override fun describeContents(): Int {
    return 0
}

companion object CREATOR : Parcelable.Creator<ModuleConfiguration> {

    const val tableName = "module_configuration"

    const val COL_ID = "id"
    const val COL_MODULE_ID = "module_id"
    const val COL_TABLE = "table"
    const val COL_FIELD_NAME = "field_name"
    const val COL_FIELD_LABEL = "field_label"
    const val COL_FIELD_TYPE = "field_type"
    const val COL_GROUP_ID = "group_id"
    const val COL_VISIBLE = "visible"
    const val COL_READ_ONLY = "read_only"
    const val COL_REQUIRED = "required"
    const val COL_POSITION = "position"
    const val COL_CREATED_AT = "created_at"
    const val COL_UPDATED_AT = "updated_at"
    const val COL_CLIENT_ID = "client_id"

    override fun createFromParcel(parcel: Parcel): ModuleConfiguration {
        return ModuleConfiguration(parcel)
    }

    override fun newArray(size: Int): Array<ModuleConfiguration?> {
        return arrayOfNulls(size)
    }
}
}

由于该列属于另一个名为Group的实体，所以我试图将其设为外键，但当我这样做时，会出现以下错误

SQLiteConstraintException:外键约束失败（代码787）

在网上搜索时，我在stackoverflow上找到了以下答案：

或

但这并没有帮助我，因为这些答案建议将int或long等基本类型更改为Integer或long等非基本类型，以允许它们为null。我已经在使用字符串作为类型

任何帮助都将不胜感激

---

提前谢谢。

请尝试重新表述这个问题，因为它确实很难理解，这就是为什么你会被否决@被否决的人：如果你留下评论，那就太好了。好的，现在就做：（现在好点了吗？是不是另一个外键

moduleId

的约束问题不可为空？也许你是对的，一旦我删除了两个外键约束，它就工作了..删除我认为是导致问题的外键也没能解决..经过一些尝试..我想这可能是顺序问题。。我是如何添加值的…因为有相当多的行是我启动数据库时使用的..现在检查它们

@Entity(
tableName = Group.tableName,
primaryKeys = [Group.COL_ID]
)
class Group(
@ColumnInfo(name = COL_ID)
var id: String = UUID.randomUUID().toString(),

@ColumnInfo(name = COL_NAME)
var name: String,

@ColumnInfo(name = COL_CREATED_AT)
var createdAt: Long = CustomDateTimeUtil.getTodayInUTC(),

@ColumnInfo(name = COL_UPDATED_AT)
var updatedAt: Long = CustomDateTimeUtil.getTodayInUTC()
) : Cloneable, Parcelable  {

constructor(parcel: Parcel) : this(
    parcel.readString() ?: "",
    parcel.readString() ?: "",
    parcel.readLong(),
    parcel.readLong()
) {
}

override fun equals(other: Any?): Boolean {
    return super.equals(other)
}

override fun hashCode(): Int {
    return super.hashCode()
}

override fun clone(): Any {
    return super.clone()
}

override fun writeToParcel(parcel: Parcel, flags: Int) {
    parcel.writeString(id)
    parcel.writeString(name)
    parcel.writeLong(createdAt)
    parcel.writeLong(updatedAt)
}

override fun describeContents(): Int {
    return 0
}

companion object CREATOR : Parcelable.Creator<Group> {

    const val tableName = "group"

    const val COL_ID = "id"
    const val COL_NAME = "name"
    const val COL_CREATED_AT = "created_at"
    const val COL_UPDATED_AT = "updated_at"
    const val COL_CLIENT_ID = "client_id"

    override fun createFromParcel(parcel: Parcel): Group {
        return Group(parcel)
    }

    override fun newArray(size: Int): Array<Group?> {
        return arrayOfNulls(size)
    }
}
}

@ColumnInfo(name = COL_GROUP_ID)
var groupId: String?,