Q:

Android room - id of insterted row - from ViewModel

I am using Android Room, and I would like to get ID of new inserted row. I have declared column in my model class:
@PrimaryKey (autoGenerate = true)
@ColumnInfo (name = "productID")
int id;

And then I know I can retrive it by dao returning long:
@Insert
long insert(Product p);

At first I was using "thread" calls directly in View. And as you know, it is not recommended method. So I am trying to change it for ModelView and repository. But I don't know how can I get this ID.
My repository class:
public class ProductRepository {

private ProductDao mProductDao;

ProductRepository(Application application) {
    AppDatabase db = AppDatabase.getDatabase(application);
    mProductDao = db.pDao();
}

public void insertProduct(Product p) {
    new insertAsyncTask(mProductDao).execute(p);
}

private static class insertAsyncTask extends AsyncTask<Product, Void, Void> {

    private ProductDao mAsyncTaskDao;

    insertAsyncTask(ProductDao dao) {
        mAsyncTaskDao = dao;
    }

    @Override
    protected Void doInBackground(final Product... params) {
        mAsyncTaskDao.insert(params[0]);
        return null;
    }
}
}

And my model class:
public class ProductModelView extends AndroidViewModel {

private ProductRepository mRepository;

public ProductModelView(Application application) {
    super(application);
    mRepository = new ProductRepository(application);
}

public void insert(Product p) {
    mRepository.insertProduct(p);
}
}

And in my Activity I am inserting new object like this:
mProductModelView.insert(pc);

So how I can retrive this long value from "insert" and get it in my activity? I guess LiveData could be a good way to go, but to be honest I dont havy any ideas how to achieve it :( 

A:

The best way to do this is by using LiveData. If you want to use MVVM might as well learn how to use LiveData. It's easy.
In your DAO interface, declare a method like this:
@Query("SELECT * FROM Product ORDER BY id DESC LIMIT 1")
LiveData<Product> getLastProductLive();

This method returns the last Product inserted as LiveData
Then inside your Repository:
public LiveData<Product> getLastProductLive(){
    return mProductDao.getLastProductLive();
}

And then inside your ViewModel:
public LiveData<Product> getLastProductLive(){
    return mRepository.getLastProductLive();
}

And finally inside your Activity:
mProductViewModel.getLastProductLive().observe(this, product -> {
    long lastInsertedRowId = product.getId();
}

By using LiveData, any time that a product is added to table, it triggers this method and you can get the id of the last inserted row.

