LINQ error - The method 'Sum' is not supported

Question

I am having following linq -

var quantity = (from p in context.StoreInventory
                         where p.BookId== BookId
                                && p.StoreAddress == StoreAddress
                         select p).Sum(i => i.Quantity);

I am getting error -

The method 'Sum' is not supported

Can anyone tell me the reason and required changes.

Answer 1

var quantity = (from p in context.StoreInventory
                         where p.BookId== BookId
                                && p.StoreAddress == StoreAddress
                         select p.Quantity).Sum();

This should work - the sum is performed on 'Quality' column, which is taken using select statement. That's because Sum(expression) is not supported by LINQ to Entities, but standard Sum() is.

Whole work should be done by database, so no rows will be retrieved by application - just single number.