使用Deferred< ...>在Kotlin协程的DAO房间中 [英] Using Deferred<...> in Room DAO with Kotlin Coroutines

问题描述

我正在尝试将协程与Android项目中的Room数据库一起使用.我几乎没有在线找到任何文档，我想知道是否有可能在这些方法中返回Deferred<>类型.像这样:

I'm trying to use Coroutines with a Room database in an Android project. I've found almost no documentation online, and I'm wondering if it is possible to return Deferred<> types in those methods. Something like this:

@Dao
interface MyObjectDAO {

@Query("SELECT * FROM myObject WHERE id_myObject = :idMyObject")
suspend fun readMyObjectAsync(idMyObject: Int): Deferred<MyObject>
}

我已经尝试过了，在编译时得到了Not sure how to convert a Cursor to this method's return type.

I've tried this and I get Not sure how to convert a Cursor to this method's return type at compile time.

我的依赖项是:

kapt 'androidx.room:room-compiler:2.1.0-alpha04'
implementation 'androidx.room:room-runtime:2.1.0-alpha04'
implementation 'androidx.room:room-coroutines:2.1.0-alpha04'

推荐答案

您的问题在于，您正在混合suspend ing转换器和Deferred转换器.使用其中之一，您的代码将按预期工作.

Your issue lies in that you're mixing the suspending converter and the Deferred converter. Use one or the other and your code will work as intended.

• fun readMyObjectAsync(idMyObject: Int): Deferred<MyObject>-如果您需要与Java代码接口/兼容，这是最佳选择，因为它不需要代码转换即可真正起作用.
• suspend fun readMyObjectAsync(idMyObject: Int): MyObject-如果您使用的是纯Kotlin，则可以更好地控制调用它的上下文.

• fun readMyObjectAsync(idMyObject: Int): Deferred<MyObject> - Best choice if you need to interface/be compatible with java code, since it doesn't require code transformations to actually function.
• suspend fun readMyObjectAsync(idMyObject: Int): MyObject - If you're operating on pure kotlin this will allow better control through the context it is called in.

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