Using a Stored Function in an Entity Framework 4 query - entity-framework

Question

I've got an Entity Framework 4 entity model in my program. There's a stored function I've defined in my SQL Anywhere 12.0.1 database called GuidToPrefix:
CREATE OR REPLACE FUNCTION GuidToPrefix( ID UNIQUEIDENTIFIER ) RETURNS INT AS
BEGIN
RETURN CAST( CAST( ID AS BINARY(4) ) AS INT )
END;
Following the directions in this MSDN article, I added the function to my EDMX:
<Function Name="GuidToPrefix" ReturnType="int" Aggregate="false" BuiltIn="false" NiladicFunction="false" IsComposable="true" ParameterTypeSemantics="AllowImplicitConversion" Schema="DBA">
<Parameter Name="ID" Type="uniqueidentifier" Mode="In" />
</Function>
To be totally honest, I updated the model from the database and checked off the function in the list on the first tab of the wizard. I don't know if that makes a difference or not, but I can't see why it would.
According to the article, I need to add a definition of the function in a C# class. My problem is it doesn't tell me what class to put that in. Do I add an entirely new class? Do I create a new .CS file and do something like this:
public static DbFunctions {
[EdmFunction( "CarSystemModel.Store", "GuidToPrefix" )]
public static int GuidToPrefix( Guid id ) {
throw new NotSupportedException( "Direct calls to GuidToPrefix are not supported." );
}
}
or do I put that in a partial of the entities class?
partial MyEntities {
[EdmFunction( "CarSystemModel.Store", "GuidToPrefix" )]
public static int GuidToPrefix( Guid id ) {
throw new NotSupportedException( "Direct calls to GuidToPrefix are not supported." );
}
}
I have two projects where this entity model is used. One is a class library and the model is definied in it. The other is another class library in another solution that just uses it. I've tried both examples above and the query in the second class library generates this error from the compiler in both cases:
The name 'GuidToPrefix' does not exist in the current context
Obviously I'm not doing something right. Has anyone tried this and got it to work?

Answer 1

I found the answer to this one.
Recall that I created a file with a partial of the MyEntities class in my project where the Entity Model is defined:
partial MyEntities {
[EdmFunction( "CarSystemModel.Store", "GuidToPrefix" )]
public static int GuidToPrefix( Guid id ) {
throw new NotSupportedException( "Direct calls to GuidToPrefix are not supported." );
}
}
This was fine and it all compiled. My problem wasn't here but in the project where I have to use the function.
In that project, in a class called DataInterface, I have a method with code like this:
var query = from read in context.Reads
from entry in context.Entries
.Where( e => GuidToPrefix( read.ID ) == e.PrefixID && read.ID == e.ID )
.....
The problem was that I needed to add the name of the class that contained the C# declaration of the GuidToPrefix function in the Where clause. That is, I needed to write the above expression as:
var query = from read in context.Reads
from entry in context.Entries
.Where( e => MyEntities.GuidToPrefix( read.ID ) == e.PrefixID && read.ID == e.ID )
.....
This compiles and when it runs it uses the function in the database in the LEFT OUTER JOIN as I wanted.