Calculated values on Entity Framework entities

Question

In my project, i have an entity named Product containing a property Price I need to calculate the taxes for each product so i made a Model defined function like in this tutorial http://blogs.msdn.com/b/efdesign/archive/2009/01/07/model-defined-functions.aspx

Everything works fine, Generated SQL is clean but i have a problem.

I would need to get the taxes for an entity i've just made (an Product object not stored in database). Is it possible to use a model defined function for an object like this ? If not, how Can I make a method to calculate the taxes with the same method from linq and from pure C# code ?

Thank's by advance.

Answer 1

What I would do is create a user-defined function in SQL Server, use that to fill your computed column, then simply call it from your application to fill the value in your newly-created object's tax value.

Unfortunately, last time I checked, it's rather clumsy calling a UDF in EF4, so what I did, and I know this isn't the cleanest thing in the world, is add a LINQ-to-SQL data context, add the UDF to that , and then just call the UDF as though it were a C# method from there.

To make things a bit cleaner, I went one more step and added the same method definition to my EF4 ObjectContext (by hand, via a partial class) and then called the method on my EF context, which then called the method on an instance of the L2S context.

I know it seems like a lot, but it's not too bad at all in practice. Calling UDFs in EF4 is the one thing that's not quite as convenient as L2S.