Question

I have an object with a Flag enum with several possible “uses”. The flag enum uses the proper power of 2.

Checking if a variable has a certain flag on, I can do it using the .NET 4 HasFlag()

BUT:

If I store that flag combination as a int in database… how can I retrive the objects that have certain flag on using Entity Framework?

For example, if my object is a “Contact” type, I would like to query those of them that are actually “Customers and Friends”, being Customers and Friends flags in the ContactType Enum.

Answer 1

I doubt any ORM is going to have a way to adapt the HasFlags down to the appropriate SQL code for your DBMS.

What you are likely going to need to do is either write a stored procedure, or hand-crank the SQL Statement to be executed for this.

You don’t mention what DBMS you’re using – but if I assume you’re using SQL Server, you are in luck as it has the & (Bitwise AND) operator.

Practical example as T-SQL:

-- Setup Test Data 
DECLARE @Contacts TABLE (id int, contactType int, name nvarchar(MAX)) 

INSERT INTO @Contacts VALUES (1, 0, 'Fred'); -- Not Wanted
INSERT INTO @Contacts VALUES (2, 3, 'Jim');  -- Wanted
INSERT INTO @Contacts VALUES (3, 36, 'Mary');  -- Not wanted
INSERT INTO @Contacts VALUEs (4, 78, 'Jo');  -- Wanted

-- Execute Query
SELECT *
FROM @Contacts
WHERE ContactType & 2 = 2