Android Room persistence library @Update not working

Question

I am trying to update my database via new android room library, but it is not working. Here it is my approach

@IgnoreExtraProperties
@Entity(tableName = CarModel.TABLE_NAME,
    indices = {@Index(value = "car_name", unique = true)})
public class CarModel {

    public static final String TABLE_NAME = "cars";

    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "car_name")
    private String name;

    @ColumnInfo(name = "car_price")
    private String price;

    private String type;
    private String position;
}

MainActivity.java

viewModel.isCarsEmpty().observe(MainActivity.this, new Observer<Integer>() {
                    @Override
                    public void onChanged(@Nullable Integer rowCount) {
                        if (rowCount == 0) {
                            viewModel.insertItems(list);
                        } else {
                            viewModel.updateItems(list);
                        }
                    }
                });

CarViewModel.java

public LiveData<Integer> isCarsEmpty() {
    return appDatabase.carDao().isDbEmpty();
}
    public void insertItems(List<CarModel> carModels) {
    new insertCarsAsyncTask(appDatabase).execute(carModels);
}

private class insertCarsAsyncTask extends AsyncTask<List<CarModel>, Void, Void> {
    private AppDatabase db;

    public insertCarsAsyncTask(AppDatabase appDatabase) {
        db = appDatabase;
    }

    @Override
    protected Void doInBackground(List<CarModel>... params) {
        db.carDao().insertCars(params[0]);
        return null;
    }
}

public void updateItems(List<CarModel> list) {
    new updateCarsTask(appDatabase).execute(list);
}

private class updateCarsTask extends AsyncTask<List<CarModel>, Void, Void> {
    private AppDatabase db;

    public updateCarsTask(AppDatabase appDatabase) {
        db = appDatabase;
    }

    @Override
    protected Void doInBackground(List<CarModel>... params) {
        db.carDao().updateCars(params[0]);
        return null;
    }
}

CarDao.java

@Insert(onConflict = REPLACE)
void insertCars(List<CarModel> cars);

@Update
void updateCars(List<CarModel> param);

@Query("SELECT count(*) FROM " + CarModel.TABLE_NAME)
LiveData<Integer> isDbEmpty();

I did debugging, new data comes and calling viewModel.updateItems(list) method.Thanks in advance!

score 38 · Answer 1 · answered Mar 06 '18 at 08:00

38

Make sure the row you want to updated and model you are sending to update should have same id which you have defined as primary key.

answered Mar 06 '18 at 08:00

Kimmi Dhingra

2,249
22
21

a really simple and useful answer – Amir Dec 25 '21 at 17:53

score 9 · Accepted Answer · answered Jul 25 '17 at 10:48

9

I am sorry for posting this as an answer but I am not allowed to add a simple comment yet so here is my idea:

Have you tried using only insertCars() instead of updateCars()? Anyway it looks like your isCarsEmpty() LiveData callback gets triggered the whole time because when the observer is called the Database is altered again.. I am not quite sure what you want to accomplish tho.

answered Jul 25 '17 at 10:48

maperz

196
3
11

Great idea, only insertCars() did the trick what i want. Thank you again. – nAkhmedov Jul 25 '17 at 11:05
Glad that i could help :) – maperz Jul 25 '17 at 12:18
1

i have an issue when using insert with `onConflict = OnConflictStrategy.REPLACE` and the entity has ` @PrimaryKey(autoGenerate = true)`, the entry was inserted with new id instead of updating the entry with same ID. Any advice? – etomun May 04 '20 at 08:41
@etomun if you set `autoGenerate=true` then you'll have to firstly obtain the entity that you want to update, then use the id from that to build your new entity. – dumbfingers Jan 12 '21 at 18:19
@dumbfingers Ok, so I need two db operations yah? – etomun Jan 13 '21 at 03:42
1

@etomun in the case of `autoGenerate=true`, yes. – dumbfingers Jan 13 '21 at 08:53

moamarubuntu · Answer 3 · 2019-07-01T08:33:15.020

The update means you fetch a CarModel which is already in the database and after updating this CarModel you return the new values to the Database, except the Id you return the same Id

what to do

you need for example a global variable of type CarModel and implement set functions in the CarModel

In MainActivity assignt the fetched CarModel to the global variable and use the set functions to update the values of member variables of the CarModel

then pass this global variable to the update function in MainActivity

I have example in my Github like this

Android Room persistence library @Update not working

3 Answers3

Linked