Android Room 和嵌套关系错误

Question

我有以下 3 个实体：

@Entity(tableName = "PROPERTY",
    indices = [
        androidx.room.Index(value = ["id"], unique = true)
    ])
data class Property (
    @Expose @PrimaryKey override val id: UUID = UUID.randomUUID(),
    @SerializedName("type") @ColumnInfo(name = "type") val type: ItemPropertyType,
    @SerializedName("code") @ColumnInfo(name = "code") val code: String,
    @SerializedName("default_description") @ColumnInfo(name = "default_description") val defaultDescription: String?,
    @SerializedName("description_id") @ColumnInfo(name = "description_id") val descriptionId: UUID?,
    @SerializedName("default_property") @ColumnInfo(name = "default_property") val defaultProperty: Boolean,
    @SerializedName("entity") @ColumnInfo(name = "entity") val entity: String = "ITEM"
)

@Entity(tableName = "PROPERTY_SET_DETAIL",
    indices = [
        Index(value = ["id"], unique = true),
        Index(value = ["property_id"], unique = false)
    ],
    foreignKeys = [
        ForeignKey(entity = PropertySet::class, parentColumns = ["id"], childColumns = ["property_set_id"]),
        ForeignKey(entity = Property::class, parentColumns = ["id"], childColumns = ["property_id"])])
data class PropertySetDetail (
    @Expose @PrimaryKey override val id: UUID = UUID.randomUUID(),
    @SerializedName("property_id") @ColumnInfo(name = "property_id") val propertyId: UUID,
    @SerializedName("value") @ColumnInfo(name = "value") var value: String?,
    @SerializedName("rank") @ColumnInfo(name = "rank") val rank: Int,
    @SerializedName("property_set_id") @ColumnInfo(name = "property_set_id") val propertySetId: UUID
)

@Entity(tableName = "PROPERTY_SET",
    indices = [Index(value = ["id"], unique = true), Index(value = ["properties_charset"], unique = false), Index(value = ["hashkey"], unique = false)])
data class PropertySet (
    @Expose @PrimaryKey override val id: UUID = UUID.randomUUID(),
    @SerializedName("item_id") @ColumnInfo(name = "item_id") val itemId: UUID,
    @SerializedName("properties_charset") @ColumnInfo(name = "properties_charset") var propertiesCharset: String?,
    @SerializedName("hashkey") @ColumnInfo(name = "hashkey") var hashkey: String?,
)

以及上面声明的 3 个实体之间的嵌套关系所需的以下数据类：

data class PropertySetAndDetails(
    @Embedded
    val set: PropertySet,

    @Relation(
        entity = PropertySetDetail::class,
        parentColumn = "id",
        entityColumn = "property_set_id"
    ) val details: List<PropertyDetailAndProperty>,
) 

data class PropertyDetailAndProperty(
    @Embedded
    val property: Property,

    @Relation(
        parentColumn = "id",
        entityColumn = "property_id"
    ) val detail: PropertySetDetail

)

以及如下DAO查询函数：

@Transaction
@Query("select * from property_set where item_id = :itemId")
suspend fun getSetsForItem(itemId: UUID): List<PropertySetAndDetails>

没有办法让它工作。我收到以下构建错误：

错误：查询有问题：[SQLITE_ERROR] SQL 错误或 缺少数据库（没有这样的列：类型）

我还为

声明了以下转换函数

项目属性类型：

@TypeConverter
    fun toItemPropertyType(v: Byte?): ItemPropertyType {
        return when (v) {
            null -> ItemPropertyType.Unknown
            else -> ItemPropertyType.getByValue(v)
        }
    }

    @TypeConverter
    fun fromItemPropertyType(t: ItemPropertyType?): Byte {
        return when (t) {
            null -> ItemPropertyType.Unknown.value
            else -> t.value
        }
    }

有人能解释一下为什么这种嵌套关系不起作用吗？提前致谢。

Answer 1

谁能解释一下为什么这种嵌套关系不起作用？

我不能（我们称它为 Room 的魔法），但我可以提示您如何使这项工作发挥作用。尝试将您的 PropertyDetailAndProperty 类更改为：

data class PropertyDetailAndProperty(
    @Embedded
    val detail: PropertySetDetail,

    @Relation(
        parentColumn = "property_id",
        entityColumn = "id"
    ) val property: Property
)

似乎嵌套类应该包含您在外部类中使用的实体（在您的情况下为PropertySetDetail），而不是@Relation。为什么？好吧，我猜这只是开发人员的设计。

Answer 2

您是否尝试过使用转换器？ Room 无法识别此数据（“ItemPropertyType”）。这就是您收到此错误的原因。

Doc