room update (or insert if not exist) rows and return count changed rows

I need update and if not exist insert row to ROOM DB.

I make this: productRepository.updateProducts(productsResponse.getProductItems());

And:

@Override
public void updateProducts(final List<ProductItem> products) {
    new Thread(() -> {
        for (ProductItem item : products) {
            Product product = createProduct(item);
            productDao.insert(product);
        }
    }).start();
}

And in DAO:

@Insert
void insert(Product products);

But I have method

@Update
void update(Product product);

And I have some questions:

1. both methods is void. How can I return saved Product or boolean flag or inserted count after insert?

2. if I try call update and I have not row will it be inserted?

3. How can I update(if not - insert) row and return count updatet or inserted rows?

1. A method, annotated with @Insert can return a long. This is the newly generated ID for the inserted row. A method, annotated with @Update can return an int. This is the number of updated rows.

2. update will try to update all your fields using the value of the primary key in a where clause. If your entity is not persisted in the database yet, the update query will not be able to find a row and will not update anything.

3. You can use @Insert(onConflict = OnConflictStrategy.REPLACE). This will try to insert the entity and, if there is an existing row that has the same ID value, it will delete it and replace it with the entity you are trying to insert. Be aware that, if you are using auto generated IDs, this means that the the resulting row will have a different ID than the original that was replaced. If you want to preserve the ID, then you have to come up with a custom way to do it.

As @Danail Alexiev said @Insert can return a long. @Update can return an int.

But for what purpose are you using update? If you just want the whole object to be replaced by the new one then just specify the OnConflictStrategy

@Insert(onConflict = OnConflictStrategy.REPLACE)
void insert(Product products);

The result will be: items that don't exist will be added, items that already exist will be replaced by the new ones.

In the case you need to update just one param (like quantity for example) you can do something like this

  @Insert(onConflict = OnConflictStrategy.REPLACE)
  void insert(Product products);

  @Query("SELECT * from item WHERE id= :id")
  List<Product> getItemById(int id);

  @Query("UPDATE item SET quantity = quantity + 1 WHERE id = :id")
  void updateQuantity(int id)

  void insertOrUpdate(Product item) {
                List<Product> itemsFromDB = getItemById(item.getId())
                if (itemsFromDB.isEmpty())
                    insert(item)
                else
                    updateQuantity(item.getId())   
            }
        }

The result will be: Try looking up the item in the DB, if found update a property, if not just insert a new item. So you only need to call one method insertOrUpdate from your DAO.