Room multi-table queries can not be nested

WorkRoomDataBase.getWorkRoomDataBase(getContext().getApplicationContext()).getFailProjDao().getFailedProjects().observe(TrainFragment.this, new Observer<List<FailedProj_select>>() {
            @Override
            public void onChanged(List<FailedProj_select> failedProj_selects) {
                for (FailedProj_select f :
                        failedProj_selects) {
                    item_id += f.getScore_deducting();
                    Log.i(TAG, "onChanged: "+f.toString());
                    Toast.makeText(getActivity().getApplicationContext(),"得分"+item_id,Toast.LENGTH_SHORT).show();
                }

            }
        });

This check will be repeated as many times

 

Correctly written as: two separate parallel codes can not be nested

  WorkRoomDataBase.getWorkRoomDataBase(getContext().getApplicationContext()).getFailProjDao().getSubject(1).observe(this, new Observer<Integer>() {
            @Override
            public void onChanged(Integer integers) {
                Log.i(TAG, "onChanged: "+integers.intValue());
                item_id = 0;


            }
        });      
        WorkRoomDataBase.getWorkRoomDataBase(getContext().getApplicationContext()).getFailProjDao().getFailedProjects().observe(TrainFragment.this, new Observer<List<FailedProj_select>>() {
            @Override
            public void onChanged(List<FailedProj_select> failedProj_selects) {
                for (FailedProj_select f :
                        failedProj_selects) {
                    item_id += f.getScore_deducting();
                    Log.i(TAG, "onChanged: "+f.toString());
                    Toast.makeText(getActivity().getApplicationContext(),"得分"+item_id,Toast.LENGTH_SHORT).show();
                }

            }
        });