如何通过将另外两列相乘来更新 android 房间数据库中的列值？

Question

I have a column (A) and I want it is value to be the multiplication of column (B) by column (C).

How to implement this in android room database? What do I need to put into the Dao, the repository, the viewmodel and activity to make it work?

Answer 1

Done by the following code:

first add the following code in the Dao:

 @Query ("UPDATE table SET A = B*C")
    void multiply();

then add this AcyncTask to the repository:

private static class MultiplyAsyncTask extends AsyncTask<Void, Void, Void> {

        private SomeDao asyncTaskDao;

        MultiplyAsyncTask(SomeDao dao) {
            asyncTaskDao = dao;
        }

        @Override
        protected Void doInBackground(Void... voids) {
            asyncTaskDao.multiply();
            return null;
        }
    }

. . . and this code also should be implemented in the repository:

public void multiplyColumns(){
        MultiplyAsyncTask task = new MultiplyAsyncTask (SomeDao);
        task.execute();
    }

Then call the method in the ViewModel:

public void multiplyColumns(){
        repository.multiplyColumns();
    }

Finally, implement this method in the Activity/Fragment where the data are inserted in the table in the onActivityResult:

  SomeViewModel.insertData(data);
  SomeViewModel.multiplyColumns();

This worked with me, but please if you have better solution share it here.