room error: The columns returned by the query does not have the fields fieldname

Question

Here is a sample POJO

public class Product{
  private long id;
  private String name;
  private double price;

 ... constructor for all fields
 ... getters and setters
}

Now, in my productDAO if I have a query like this

@Query(select id, name from products)
LiveData<List<Product>> getProducts()

I get an error like:

The columns returned by the query does not have the fields [price] in ... Product even though they are annotated as non-null or primitive. Columns returned by the query: [id,name]

a) If I go in my Products and set

@Nullable
private double price;

the error remains.

b) If I go in my Products and set

@Ignore
private double price;

the error goes away but if I have another query for instance

 @Query(select p.id, p.name, p.price, t.someField from products p inner join table t)
    LiveData<List<Product>> getJoinQueryResponse()

because @Ignore is set the price is returned as 0.0.

So how to solve this? Hopefully I don't need to make a POJO for each different response from room...

Answer 1

Primitive types are by default not null. Make the price Double and this will solve the issue since it will be nullable then. Furthermore, you can add a custom getter to avoid having price as a null object.

public double getPrice(){
    if(this.price == null) return 0.0;
    return this.price;
}

@Ingore tells Room to ignore the field altogether, which is not what you want, based on your answer.