英文:
Room @Transaction not working with Flowable
问题
我在使用@Transaction注解在我的数据源方法上遇到了问题。在我的情况下，这个注解似乎不起作用。
我有一个常规的Room数据库和DAO：
@Database(entities = [MyEntity::class], version = 1)
abstract class MyDatabase : RoomDatabase() {
abstract fun myDao(): MyDao
}
@Dao
interface MyDao {
@Insert
fun insertAll(list: List<MyEntity>)
@Query("SELECT * FROM MyEntity")
fun observe(): Flowable<List<MyEntity>>
@Query("DELETE FROM MyEntity")
fun clear()
}
问题出现在我连续使用clear()和insertAll()时的数据源中：
class MyDataSource(database: MyDatabase) {
private val myDao = database.myDao()
@Transaction
fun updateMyEntity(items: List<MyEntity>) {
myDao.clear()
myDao.insertAll(items)
}
fun observeMyEntity(): Flowable<List<MyEntity>> {
return myDao.observe()
}
}
当我调用updateMyEntity()时，在我的oberveMyEntity()订阅中会得到两个结果。第一个结果是空列表，第二个结果是插入的列表。我期望只得到插入的列表，因为我在updateMyEntity()方法上添加了@Transaction注解。这个注解在我的情况下不起作用吗？
我在文档中看到了以下信息，但我不确定是否适用于我的情况：
如果查询是异步的（例如返回{@link androidx.lifecycle.LiveData LiveData}或RxJava {@code Flowable}），事务会在查询运行时得到正确处理，而不是在方法调用时。
将此注解放在{@link Insert}、{@link Update}或{@link Delete}方法上没有任何影响，因为这些方法总是在事务内部运行。类似地，如果一个方法被{@link Query}注解标记，但运行的是INSERT、UPDATE或DELETE语句，它会自动被包装在一个事务中，这个注解不起作用。
如果将database设置为属性，并使用database.runInTransaction { }包装调用clear()和insertAll()，问题就会消失。
英文:
I have a problem with using @Transaction annotation on my data source method. Looks like this annotation not working in my case.
I have a usual room database with DAO
@Database(entities = [MyEntity::class], version = 1)
abstract class MyDatabase : RoomDatabase() {
abstract fun myDao(): MyDao
}
@Dao
interface myDao {
@Insert
fun insertAll(list: List<MyEntity>)
@Query("SELECT * FROM MyEntity")
fun observe(): Flowable<List<MyEntity>>
@Query("DELETE FROM MyEntity")
fun clear()
}
Problem appears in my data source when I do consistently clear() and insertAll()
class MyDataSource(database: MyDatabase) {
private val myDao = database.myDao()
@Transaction
fun updateMyEntity(items: List<MyEntity>) {
myDao.clear()
myDao.insertAll(items)
}
fun observeMyEntity(): Flowable<List<MyEntity>> {
return myDao.observe()
}
}
When I call updateMyEntity(), I get two results in my subscription on oberveMyEntity(). The first result is empty list and the second one is inserted list. I expected to get only inserted list as I added annotation @Transaction to method updateMyEntity(). Is this annotation not working in my case?
I saw in docs the following information, but I am not sure is it my case or not.
> If the query is asynchronous (e.g. returns a {@link androidx.lifecycle.LiveData LiveData}
or RxJava {@code Flowable}), the transaction is properly handled when the query is run, not when
the method is called.
>
> Putting this annotation on an {@link Insert}, {@link Update} or {@link Delete} method has no
impact because those methods are always run inside a transaction. Similarly, if a method is
annotated with {@link Query} but runs an INSERT, UPDATE or DELETE statement, it is automatically wrapped in a transaction and this annotation has no effect.
The problem disappears if make database a property and wrap calls clear() and insertAll() with database.runInTransaction { }.
答案1
得分: 1
Transaction 只能用于 Dao 方法。
英文:
Transaction can only be used for Dao methods
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