Question

我对表之间的关系非常熟悉，尤其是在使用SQLite时。最近，我考虑到MVVM干净的体系结构迁移到Room，在建立关系时遇到了很多困惑。

为简单起见，我获取Github存储库列表并使用Room存储在数据库中。

这是JSON

[
{
"author": "idealvin",
"name": "co",
"avatar": "https://github.com/idealvin.png",
"url": "https://github.com/idealvin/co",
"description": "An elegant and efficient C++ basic library for Linux, Windows and Mac.",
"language": "C++",
"languageColor": "#f34b7d",
"stars": 635,
"forks": 82,
"currentPeriodStars": 130,
"builtBy": [
{
"username": "idealvin",
"href": "https://github.com/idealvin",
"avatar": "https://avatars1.githubusercontent.com/u/12691466"
},
{
"username": "frederick-vs-ja",
"href": "https://github.com/frederick-vs-ja",
"avatar": "https://avatars3.githubusercontent.com/u/23228989"
},
{
"username": "FrankHB",
"href": "https://github.com/FrankHB",
"avatar": "https://avatars0.githubusercontent.com/u/1857647"
}
]
},
{
"author": "alyssaxuu",
"name": "flowy",
"avatar": "https://github.com/alyssaxuu.png",
"url": "https://github.com/alyssaxuu/flowy",
"description": "The minimal javascript library to create flowcharts ✨",
"language": "JavaScript",
"languageColor": "#f1e05a",
"stars": 1841,
"forks": 58,
"currentPeriodStars": 459,
"builtBy": [
{
"username": "alyssaxuu",
"href": "https://github.com/alyssaxuu",
"avatar": "https://avatars3.githubusercontent.com/u/7581348"
},
{
"username": "artmsilva",
"href": "https://github.com/artmsilva",
"avatar": "https://avatars3.githubusercontent.com/u/347490"
}
]
}
]

这是我的Entity类。

@Entity
data class GithubEntity(


    // Ignore this field during Serialization and De-Serialization
    // PK  (AUTO INC)
    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "rowId")
    @Expose(serialize = false, deserialize = false) var rowId: Int,

    @ColumnInfo(name = "author")
    @SerializedName("author")
    @Expose var author: String? = null,

    @ColumnInfo(name = "name")
    @SerializedName("name")
    @Expose var name: String? = null,

    @ColumnInfo(name = "avatar")
    @SerializedName("avatar")
    @Expose var avatar: String? = null,

    @ColumnInfo(name = "url")
    @SerializedName("url")
    @Expose var url: String? = null,

    @ColumnInfo(name = "description")
    @SerializedName("description")
    @Expose var description: String? = null,

    @ColumnInfo(name = "language")
    @SerializedName("language")
    @Expose var language: String? = null,

    @ColumnInfo(name = "languageColor")
    @SerializedName("languageColor")
    @Expose var languageColor: String? = null,

    @ColumnInfo(name = "stars")
    @SerializedName("stars")
    @Expose var stars: Int? = null,

    @ColumnInfo(name = "forks")
    @SerializedName("forks")
    @Expose var forks: Int? = null,

    @ColumnInfo(name = "currentPeriodStars")
    @SerializedName("currentPeriodStars")
    @Expose var currentPeriodStars: Int? = null,


   
    @SerializedName("builtBy")
    @Expose var builtByList: List<BuiltByEntity>? = null


) {

    constructor() : this(
        0, "", "", "", "",
        "", "", "", 0, 0, 0, null
    )

}

@Entity(
    foreignKeys = [ForeignKey(
        entity = GithubEntity::class,
        parentColumns = arrayOf("rowId"),
        childColumns = arrayOf("rowFkId"),
        onDelete = ForeignKey.CASCADE
    )]
)
data class BuiltByEntity(

    // PK (AUTO INC)
    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "row_Built_Id")
    @Expose(serialize = false, deserialize = false) var rowId: Int,


    // FOREIGN KEY -> rowId (PK) of GitHubEntity
    @ColumnInfo(name = "rowFkId")
    @Expose(serialize = false, deserialize = false) var rowFkId: Int,

    @ColumnInfo(name = "username")
    @SerializedName("username")
    @Expose var username: String? = null,

    @ColumnInfo(name = "href")
    @SerializedName("href")
    @Expose var href: String? = null,

    @ColumnInfo(name = "avatar")
    @SerializedName("avatar")
    @Expose var avatar: String? = null
) {

    constructor() : this(0, 0, "", "", "")
}

还有我的AppDataBase类

   @Database(entities = [GithubEntity::class, BuiltByEntity::class], version = 1, exportSchema = false)
@TypeConverters(BuiltByConverter::class)
abstract class AppDatabase : RoomDatabase() {

所以，我期待这样的输出

GitHubEntity的rowId（PK）在BuiltByEnity rowFkId（FK）中用作FK

所以，当我使用Stetho进行调试时，这是我得到的输出

我在转弯房间方面遇到困难。您能强调一下哪些地方应该修改吗？

Answer 1

一种解决方法是删除此内容：

@SerializedName("builtBy")
@Expose var builtByList: List<BuiltByEntity>? = null

来自GithubEntity。插入一个GithubEntity项，并通过其ID插入BuiltByEntity。

你看，这很讨厌。请注意，在房间中没有插入关系的本地方法。阅读this问答，以获取最佳做法。

更新：

也请阅读此文章：Android Room Database Tips and Tricks

桌子问题之间的房间关系

1 个答案: