Android：如果我删除唯一的子项，为什么 Room 会删除父项？

问题描述 投票：0回答：1

我正在为 Android 应用程序使用 Room。

@Entity(tableName = "author")
data class AuthorEntity(
@PrimaryKey
@ColumnInfo(name = "authorId")
val authorId: String,
@ColumnInfo(name = "name")
val name: String?

@Entity(tableName = "book")
data class BookEntity(
@PrimaryKey
@ColumnInfo(name = "bookId")
val bookId: String,
@ColumnInfo(name = "title")
val title: String?

@Entity(
    tableName = "author_book",
    primaryKeys = ["authorId", "bookId"],
    foreignKeys = [
        ForeignKey(
            entity = AuthorEntity::class,
            parentColumns = arrayOf("authorId"),
            childColumns = arrayOf("authorId"),
            onDelete = ForeignKey.CASCADE,
            onUpdate = ForeignKey.CASCADE
        ),
        ForeignKey(
            entity = BookEntity::class,
            parentColumns = arrayOf("bookId"),
            childColumns = arrayOf("bookId"),
            onDelete = ForeignKey.CASCADE,
            onUpdate = ForeignKey.CASCADE
        )
    ]
)
data class AuthorBookCrossRef(
    val authorId: String,
    val bookId: String,
    val desc: String
)

data class NewsWithSectionWithContract(
    @Embedded val authorEntity: AuthorEntity,
    @Relation(
        parentColumn = "authorId",
        entityColumn = "bookId",
        associateBy = Junction(
            AuthorBookCrossRef::class
        )
    )
    var bookEntities: List<BookEntity>
)

如果我删除 BookEntity，它应该只删除 AuthorBookCrossRef 行，那么为什么它也删除 AuthorEntity？

android foreign-keys android-room rdbms cascade
1个回答
0
投票

我相信你弄错了或没有检查实际数据。

使用您提供的代码，另外：-

@Dao
interface AllDAOs{
    @Insert(onConflict = OnConflictStrategy.IGNORE)
    fun insert(authorEntity: AuthorEntity): Long
    @Insert(onConflict = OnConflictStrategy.IGNORE)
    fun insert(bookEntity: BookEntity): Long
    @Insert(onConflict = OnConflictStrategy.IGNORE)
    fun insert(authorBookCrossRef: AuthorBookCrossRef): Long

    @Delete
    fun delete(authorBookCrossRef: AuthorBookCrossRef): Int
    @Delete
    fun delete(bookEntity: BookEntity): Int
    @Delete
    fun delete(authorEntity: AuthorEntity): Int

    @Query("SELECT * FROM author")
    fun getAllAuthors(): List<AuthorEntity>
    @Query("SELECT * FROM book")
    fun getAllBooks(): List<BookEntity>
    @Query("SELECT* FROM author_book")
    fun getAllAuthorBookRefs(): List<AuthorBookCrossRef>
    @Transaction
    @Query("SELECT * FROM author")
    fun getAllAuthorsWithBooks(): List<NewsWithSectionWithContract>
}

@Database(entities = [AuthorEntity::class,BookEntity::class,AuthorBookCrossRef::class], version = 1, exportSchema = false)
abstract class TheDatabase: RoomDatabase() {
    abstract fun getAllDAOs(): AllDAOs

    companion object {
        var instance: TheDatabase?=null
        fun getInstance(context: Context): TheDatabase {
            if (instance==null) {
                instance = Room.databaseBuilder(context,TheDatabase::class.java,"the_database.db")
                    .allowMainThreadQueries()
                    .build()
            }
            return instance as TheDatabase
        }
    }
}

然后在活动中：-

class MainActivity : AppCompatActivity() {
    lateinit var db: TheDatabase
    lateinit var dao: AllDAOs
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        db = TheDatabase.getInstance(this)
        dao = db.getAllDAOs()

        dao.insert(AuthorEntity("LC001","Lewis Carrol"))
        dao.insert(AuthorEntity("JS001","John Steinbeck"))
        dao.insert(AuthorEntity("WS001","William Shakespeare"))
        dao.insert(AuthorEntity("CD001","Charles Dickens"))

        dao.insert(BookEntity("b001","David Copperfield"))
        dao.insert(BookEntity("b002","Oliver"))
        dao.insert(BookEntity("b003","Alice in Wonderland"))
        dao.insert(BookEntity("b004","Alice through the Looking Glass"))
        dao.insert(BookEntity("b005","The Lion, the Witch and the Wardrobe"))
        dao.insert(BookEntity("b006","Wrath of the grapes"))
        dao.insert(BookEntity("b007","Day of the Triffids"))
        dao.insert(BookEntity("b008","Something"))

        dao.insert(AuthorBookCrossRef("LC001","b003","AIW"))
        dao.insert(AuthorBookCrossRef("LC001","b004","ATTLG"))
        dao.insert(AuthorBookCrossRef("JS001","b007","DOTT"))
        dao.insert(AuthorBookCrossRef("JS001","b006","WOTG"))
        dao.insert(AuthorBookCrossRef("CD001","b001","DC"))
        dao.insert(AuthorBookCrossRef("CD001","b002","O"))

        logAllData("_STAGE1")

        dao.delete(BookEntity("b004","does not matter!!!!"))

        logAllData("_STAGE2")

    }

    fun logAllData(tagSuffix: String) {
        val tag = "DBINFO_"
        Log.d(tag + tagSuffix,"ALL Authors")
        for (a in dao.getAllAuthors()) {
            Log.d(tag + tagSuffix,"\tAuthor is ${a.name} ID is ${a.authorId}")
        }
        Log.d(tag + tagSuffix,"ALL Books")
        for (b in dao.getAllBooks()) {
            Log.d(tag + tagSuffix,"\tBook is ${b.title} ID is ${b.bookId}")
        }
        Log.d(tag + tagSuffix,"All Author Book Refs")
        for (ab in dao.getAllAuthorBookRefs()) {
            Log.d(tag + tagSuffix,"\t AID is ${ab.authorId} BID is ${ab.bookId} DESC is ${ab.desc}")
        }
        Log.d(tag + tagSuffix,"Authors with Books")
        for (awb in dao.getAllAuthorsWithBooks()) {
            val sb=StringBuilder()
            for (b in awb.bookEntities) {
                sb.append("\n\t\tBook is ${b.title} BID is ${b.bookId}")
            }
            Log.d(tag + tagSuffix,"Author is ${awb.authorEntity.name}. Has ${awb.bookEntities.size} Books. They are:$sb" )
        }
    }
}

那么可以看出删除id为“b004”的书并没有删除作者

在删除之前，日志的输出是：-

2023-05-18 06:57:57.556 D/DBINFO__STAGE1: ALL Authors
2023-05-18 06:57:57.563 D/DBINFO__STAGE1:   Author is Lewis Carrol ID is LC001
2023-05-18 06:57:57.563 D/DBINFO__STAGE1:   Author is John Steinbeck ID is JS001
2023-05-18 06:57:57.563 D/DBINFO__STAGE1:   Author is William Shakespeare ID is WS001
2023-05-18 06:57:57.564 D/DBINFO__STAGE1:   Author is Charles Dickens ID is CD001
2023-05-18 06:57:57.564 D/DBINFO__STAGE1: ALL Books
2023-05-18 06:57:57.565 D/DBINFO__STAGE1:   Book is David Copperfield ID is b001
2023-05-18 06:57:57.565 D/DBINFO__STAGE1:   Book is Oliver ID is b002
2023-05-18 06:57:57.565 D/DBINFO__STAGE1:   Book is Alice in Wonderland ID is b003
2023-05-18 06:57:57.565 D/DBINFO__STAGE1:   Book is Alice through the Looking Glass ID is b004
2023-05-18 06:57:57.565 D/DBINFO__STAGE1:   Book is The Lion, the Witch and the Wardrobe ID is b005
2023-05-18 06:57:57.565 D/DBINFO__STAGE1:   Book is Wrath of the grapes ID is b006
2023-05-18 06:57:57.565 D/DBINFO__STAGE1:   Book is Day of the Triffids ID is b007
2023-05-18 06:57:57.565 D/DBINFO__STAGE1:   Book is Something ID is b008
2023-05-18 06:57:57.565 D/DBINFO__STAGE1: All Author Book Refs
2023-05-18 06:57:57.566 D/DBINFO__STAGE1:    AID is LC001 BID is b003 DESC is AIW
2023-05-18 06:57:57.566 D/DBINFO__STAGE1:    AID is LC001 BID is b004 DESC is ATTLG
2023-05-18 06:57:57.566 D/DBINFO__STAGE1:    AID is JS001 BID is b007 DESC is DOTT
2023-05-18 06:57:57.566 D/DBINFO__STAGE1:    AID is JS001 BID is b006 DESC is WOTG
2023-05-18 06:57:57.566 D/DBINFO__STAGE1:    AID is CD001 BID is b001 DESC is DC
2023-05-18 06:57:57.566 D/DBINFO__STAGE1:    AID is CD001 BID is b002 DESC is O
2023-05-18 06:57:57.566 D/DBINFO__STAGE1: Authors with Books
2023-05-18 06:57:57.575 D/DBINFO__STAGE1: Author is Lewis Carrol. Has 2 Books. They are:
            Book is Alice in Wonderland BID is b003
            Book is Alice through the Looking Glass BID is b004
2023-05-18 06:57:57.575 D/DBINFO__STAGE1: Author is John Steinbeck. Has 2 Books. They are:
            Book is Wrath of the grapes BID is b006
            Book is Day of the Triffids BID is b007
2023-05-18 06:57:57.575 D/DBINFO__STAGE1: Author is William Shakespeare. Has 0 Books. They are:
2023-05-18 06:57:57.575 D/DBINFO__STAGE1: Author is Charles Dickens. Has 2 Books. They are:
            Book is David Copperfield BID is b001
            Book is Oliver BID is b002

在删除 b004 书之后：-

2023-05-18 06:57:57.577 D/DBINFO__STAGE2: ALL Authors
2023-05-18 06:57:57.579 D/DBINFO__STAGE2:   Author is Lewis Carrol ID is LC001
2023-05-18 06:57:57.579 D/DBINFO__STAGE2:   Author is John Steinbeck ID is JS001
2023-05-18 06:57:57.579 D/DBINFO__STAGE2:   Author is William Shakespeare ID is WS001
2023-05-18 06:57:57.580 D/DBINFO__STAGE2:   Author is Charles Dickens ID is CD001
2023-05-18 06:57:57.580 D/DBINFO__STAGE2: ALL Books
2023-05-18 06:57:57.583 D/DBINFO__STAGE2:   Book is David Copperfield ID is b001
2023-05-18 06:57:57.583 D/DBINFO__STAGE2:   Book is Oliver ID is b002
2023-05-18 06:57:57.583 D/DBINFO__STAGE2:   Book is Alice in Wonderland ID is b003
2023-05-18 06:57:57.583 D/DBINFO__STAGE2:   Book is The Lion, the Witch and the Wardrobe ID is b005
2023-05-18 06:57:57.583 D/DBINFO__STAGE2:   Book is Wrath of the grapes ID is b006
2023-05-18 06:57:57.583 D/DBINFO__STAGE2:   Book is Day of the Triffids ID is b007
2023-05-18 06:57:57.583 D/DBINFO__STAGE2:   Book is Something ID is b008
2023-05-18 06:57:57.583 D/DBINFO__STAGE2: All Author Book Refs
2023-05-18 06:57:57.585 D/DBINFO__STAGE2:    AID is LC001 BID is b003 DESC is AIW
2023-05-18 06:57:57.585 D/DBINFO__STAGE2:    AID is JS001 BID is b007 DESC is DOTT
2023-05-18 06:57:57.585 D/DBINFO__STAGE2:    AID is JS001 BID is b006 DESC is WOTG
2023-05-18 06:57:57.585 D/DBINFO__STAGE2:    AID is CD001 BID is b001 DESC is DC
2023-05-18 06:57:57.585 D/DBINFO__STAGE2:    AID is CD001 BID is b002 DESC is O
2023-05-18 06:57:57.586 D/DBINFO__STAGE2: Authors with Books
2023-05-18 06:57:57.604 D/DBINFO__STAGE2: Author is Lewis Carrol. Has 1 Books. They are:
            Book is Alice in Wonderland BID is b003
2023-05-18 06:57:57.604 D/DBINFO__STAGE2: Author is John Steinbeck. Has 2 Books. They are:
            Book is Wrath of the grapes BID is b006
            Book is Day of the Triffids BID is b007
2023-05-18 06:57:57.604 D/DBINFO__STAGE2: Author is William Shakespeare. Has 0 Books. They are:
2023-05-18 06:57:57.604 D/DBINFO__STAGE2: Author is Charles Dickens. Has 2 Books. They are:
            Book is David Copperfield BID is b001
            Book is Oliver BID is b002

即Lewis Carrol 仍然存在，即使爱丽丝镜中奇遇记已被删除（注意错误的标题已被忽略，即删除是基于主键值）。

如果最后一本书“b003”被删除，那么：-

2023-05-18 07:15:00.320 D/DBINFO__STAGE2: ALL Authors
2023-05-18 07:15:00.323 D/DBINFO__STAGE2:   Author is Lewis Carrol ID is LC001
2023-05-18 07:15:00.323 D/DBINFO__STAGE2:   Author is John Steinbeck ID is JS001
2023-05-18 07:15:00.323 D/DBINFO__STAGE2:   Author is William Shakespeare ID is WS001
2023-05-18 07:15:00.323 D/DBINFO__STAGE2:   Author is Charles Dickens ID is CD001
2023-05-18 07:15:00.323 D/DBINFO__STAGE2: ALL Books
2023-05-18 07:15:00.326 D/DBINFO__STAGE2:   Book is David Copperfield ID is b001
2023-05-18 07:15:00.326 D/DBINFO__STAGE2:   Book is Oliver ID is b002
2023-05-18 07:15:00.326 D/DBINFO__STAGE2:   Book is The Lion, the Witch and the Wardrobe ID is b005
2023-05-18 07:15:00.326 D/DBINFO__STAGE2:   Book is Wrath of the grapes ID is b006
2023-05-18 07:15:00.326 D/DBINFO__STAGE2:   Book is Day of the Triffids ID is b007
2023-05-18 07:15:00.326 D/DBINFO__STAGE2:   Book is Something ID is b008
2023-05-18 07:15:00.326 D/DBINFO__STAGE2: All Author Book Refs
2023-05-18 07:15:00.329 D/DBINFO__STAGE2:    AID is JS001 BID is b007 DESC is DOTT
2023-05-18 07:15:00.329 D/DBINFO__STAGE2:    AID is JS001 BID is b006 DESC is WOTG
2023-05-18 07:15:00.329 D/DBINFO__STAGE2:    AID is CD001 BID is b001 DESC is DC
2023-05-18 07:15:00.329 D/DBINFO__STAGE2:    AID is CD001 BID is b002 DESC is O
2023-05-18 07:15:00.329 D/DBINFO__STAGE2: Authors with Books
2023-05-18 07:15:00.334 D/DBINFO__STAGE2: Author is Lewis Carrol. Has 0 Books. They are:
2023-05-18 07:15:00.334 D/DBINFO__STAGE2: Author is John Steinbeck. Has 2 Books. They are:
            Book is Wrath of the grapes BID is b006
            Book is Day of the Triffids BID is b007
2023-05-18 07:15:00.334 D/DBINFO__STAGE2: Author is William Shakespeare. Has 0 Books. They are:
2023-05-18 07:15:00.334 D/DBINFO__STAGE2: Author is Charles Dickens. Has 2 Books. They are:
            Book is David Copperfield BID is b001
            Book is Oliver BID is b002

即刘易斯卡罗尔仍然存在，但他有 0 本书。

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