为什么 Room observer 会一遍又一遍地将同一个实体添加到数据库中？

Question

我检索了我使用 Retrofit 创建并上传到互联网的 JSON 数据。我可以成功检索和显示数据，但是当我将数据插入 Room 数据库时，只添加了最后一个 JSON 对象，似乎有 JSON 个对象.

根据我的 log，JSON 数据在 Retrofits onResponse() 方法中完整检索 - 没问题。但是根据 Room 中 getAllData() 上的 observer 方法，只有最后一个 JSON 对象被添加到 Room。观察者被触发，每个 JSON 个对象触发一次，但每次只显示最后一个 JSON 个对象。我使用 Ridill SQLlte 仔细检查了数据库文件，它证实了这一点：

我的 Log 看起来像这样：

//First observer shows nothing

D/TAG: OBSERVED

//JSON is retrieved, looks fine

D/TAG: JSON GATHERED
D/TAG: ROOM NAME: Bob
D/TAG: ROOM DATE: 3/13/2015
D/TAG: ROOM FROM: 8:00
D/TAG: ROOM UNTIL: 13:00
D/TAG: ROOM NAME: Joe
D/TAG: ROOM DATE: 1/3/2015
D/TAG: ROOM FROM: 12.30
D/TAG: ROOM UNTIL: 13:00
D/TAG: ROOM NAME: Martin
D/TAG: ROOM DATE: 1/5/2015
D/TAG: ROOM FROM: 15.30
D/TAG: ROOM UNTIL: 16:00

//Observer is set again, shows last of the JSON objects

D/TAG: OBSERVED
D/TAG ROOM: MyRoomEntity{id=1, name='Martin', date='1/5/2015', from='15.30', until='16:00'}

//Observer fires again, now having added the last JSON object a second time

D/TAG: OBSERVED
D/TAG ROOM: MyRoomEntity{id=1, name='Martin', date='1/5/2015', from='15.30', until='16:00'}
D/TAG ROOM: MyRoomEntity{id=2, name='Martin', date='1/5/2015', from='15.30', until='16:00'}

//Observer fires again, now adding the last object for a third time.

D/TAG: OBSERVED
D/TAG ROOM: MyRoomEntity{id=1, name='Martin', date='1/5/2015', from='15.30', until='16:00'}
D/TAG ROOM: MyRoomEntity{id=2, name='Martin', date='1/5/2015', from='15.30', until='16:00'}
D/TAG ROOM: MyRoomEntity{id=3, name='Martin', date='1/5/2015', from='15.30', until='16:00'}

onResponse() 方法如下所示：

public void onResponse(Call<List<RetrofitVariables>> call, Response<List<RetrofitVariables>> response) {
            List<RetrofitVariables> myResponse = response.body();
            MyRoomEntity myRoomEntity = new MyRoomEntity();

            Log.d( "TAG" , "JSON GATHERED" );

            if(myResponse != null) {
                MyRoomDatabase db = myViewModel.getRoomDatabase();

                    for(RetrofitVariables item: myResponse) {

                        Log.d( "TAG" , "name: " + item.getName());
                        Log.d( "TAG" , "from: " + item.getFrom());
                        Log.d( "TAG" , "until: " + item.getUntil());
                        Log.d( "TAG" , "Counter: " + counter);

                        myRoomEntity.setName( item.getName() );
                        myRoomEntity.setDate( item.getDate() );
                        myRoomEntity.setFrom( item.getFrom() );
                        myRoomEntity.setUntil( item.getUntil() );

                        //THESE LOGS SHOW CORRECT RESULT
                        Log.d( "TAG" , "ROOM NAME: " + myRoomEntity.getName());
                        Log.d( "TAG" , "ROOM DATE: " + myRoomEntity.getDate());
                        Log.d( "TAG" , "ROOM FROM: " + myRoomEntity.getFrom());
                        Log.d( "TAG" , "ROOM UNTIL: " + myRoomEntity.getUntil());


                        myViewModel.insertDataVM( myRoomEntity );

                    }
            }
        }

我的 observer 看起来像这样：

myViewModel.getAllDataVM().observe( this, new Observer<List<MyRoomEntity>>() {
        @Override
        public void onChanged(@Nullable List<MyRoomEntity> myRoomEntities) {
            //myAdapter.setList( myRoomEntities );

            Log.d("TAG", "OBSERVED");
            if(myRoomEntities != null) {
                for(MyRoomEntity item: myRoomEntities) {
                    Log.d("TAG ROOM ", "" + item.toString());
                }
            }
        }
    } );

在 onResponse() 方法中一切看起来都很好，那么为什么数据没有正确添加到 Room 中？如何将所有 JSON 对象放入 Room 而不仅仅是最后一个？我在这里错过了什么？

在此先感谢您的帮助！

Answer 1

您不想重复使用您的房间实体对象。移动

MyRoomEntity myRoomEntity = new MyRoomEntity();

到填充循环内部

for(RetrofitVariables item: myResponse) {
    MyRoomEntity myRoomEntity = new MyRoomEntity();
    myRoomEntity.setName( item.getName() );
    myRoomEntity.setDate( item.getDate() );
    myRoomEntity.setFrom( item.getFrom() );
    myRoomEntity.setUntil( item.getUntil() );

    myViewModel.insertDataVM( myRoomEntity );
}

为什么 Room observer 会一遍又一遍地将同一个实体添加到数据库中？

Why does Room observer add the same entity over and over again into the database?

java

android

json

observers

android-room