android - 如何插入“一对一”房间数据库
问题描述
我正在尝试在android中插入一个具有一对一关系的对象。更准确地说,我正在尝试遵循 谷歌官方文档中的示例
我正在使用两个类用户和库。我遇到的问题是如何在数据库中插入元素。我的代码是这样写的
@Entity
data class Library(
@PrimaryKey(autoGenerate = true) val libraryId: Long = 0,
val userOwnerId: Long
)
@Entity
data class User(
@PrimaryKey(autoGenerate = true) val userId: Long =0,
val name: String,
val age: Int
)
data class UserAndLibrary(
@Embedded val user: User,
@Relation(
parentColumn = "userId",
entityColumn = "userOwnerId"
)
val library: Library
)
并且插入的逻辑看起来像这样
private val repository = UserRepository(application)
fun insertUser() {
val user1 = User(name = "User1", age = 31)
val user2 = User(name = "User2", age = 32)
val library1 = Library(userOwnerId = user1.userId)
val library2 = Library(userOwnerId = user2.userId)
viewModelScope.launch {
repository.insertUser(user1)
repository.insertUser(user2)
repository.insertLibrary(library1)
repository.insertLibrary(library2)
}
存储库和 dao 类的代码如下所示
//repository
suspend fun insertUser(user: User) = appDataBase.userDao().insertUser(user)
suspend fun insertLibrary(library: Library)=appDataBase.userDao().insertLibrary(library)
//dao
@Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insertUser(user: User)
@Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insertLibrary(library: Library)
问题是库表中的外键总是0。
解决方案
我相信您的问题是由于您如何插入库数据。更具体地说,当您插入 Library 时,您是否设置了 Library 的值userOwnerId
?(我不相信或将其设置为 0)。
考虑以下使用您的类(User、Library 和 userAndLibrary)的以下@Dao 和非常标准的@Database 的问题:-
@Dao
abstract class AllDao {
@Insert(onConflict = OnConflictStrategy.REPLACE)
abstract fun insert(library: Library): Long
@Insert(onConflict = OnConflictStrategy.REPLACE)
abstract fun insert(user: User): Long
@Query("SELECT * FROM user")
abstract fun getAllUsers(): List<User>
@Query("SELECT * FROM library")
abstract fun getAllLibraries(): List<Library>
@Query("SELECT * FROM user")
abstract fun getUsersAndThierLibrary(): List<UserAndLibrary>
}
- 注意插入返回 Long(即插入行的 id)
结合上述活动中的代码(为了方便和简洁,在主线程上运行):-
db = TheDatabase.getInstance(this)
dao = db.getAllDao()
/* Explanatory Insert */
var firstUser = User(name = "Susan",age = 20)
var firstUserId = dao.insert(firstUser)
dao.insert(Library(userOwnerId = firstUserId))
/* More Concise Inserts */
dao.insert(Library(userOwnerId = dao.insert(User(name ="Fred",age = 21))))
dao.insert(Library(userOwnerId = dao.insert(User(name ="Mary",age= 19))))
for (u: User in dao.getAllUsers()) {
Log.d(TAG," User is ${u.name} ID is ${u.userId} age is ${u.age}")
}
for (l: Library in dao.getAllLibraries()) {
Log.d(TAG,"Library is ${l.libraryId} owned by ${l.userOwnerId}")
}
for(ual: UserAndLibrary in dao.getUsersAndThierLibrary()) {
Log.d(TAG,"User = ${ual.user.name} Library ID is ${ual.library.libraryId}")
}
- 再次注意在插入用户时使用返回的值( userId )。
可以看出,上面插入了 3 个用户和库。然后它提取所有用户、所有库和 UserAndLibrary。结果是:-
2021-07-31 12:29:41.888 D/MYINFO: User is Susan ID is 1 age is 20
2021-07-31 12:29:41.889 D/MYINFO: User is Fred ID is 2 age is 21
2021-07-31 12:29:41.889 D/MYINFO: User is Mary ID is 3 age is 19
2021-07-31 12:29:41.890 D/MYINFO: Library is 1 owned by 1
2021-07-31 12:29:41.890 D/MYINFO: Library is 2 owned by 2
2021-07-31 12:29:41.890 D/MYINFO: Library is 3 owned by 3
2021-07-31 12:29:41.894 D/MYINFO: User = Susan Library ID is 1
2021-07-31 12:29:41.895 D/MYINFO: User = Fred Library ID is 2
2021-07-31 12:29:41.895 D/MYINFO: User = Mary Library ID is 3
- 即一切都如预期。
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