We use an EDMX to access our database with Entity Framework. Before you comment: we have our reasons not to use code-first. Today we encountered a small problem with linq to entities and validating a varchar field that contains an integer value. Again: we have our reasons. Think about key-value pairs.

An excellent answer of Joel Mueller on stackoverflow.com helped us overcome this problem. In short we had to add a function to our edmx conceptual model. The link above has all te details.

<Function Name="ParseInt" ReturnType="Edm.Int32">
   <Parameter Name="stringvalue" Type="Edm.String"/>
   <DefiningExpression>
      CAST(stringvalue as Edm.Int32)
   </DefiningExpression>
</Function>

The validation works like a charm now. This is what EF generates (see the CAST?):

SELECT [GroupBy1].[A1] AS [C1]
FROM ( SELECT COUNT(1) AS [A1]
        FROM [dbo].[Table] AS [Extent1]
        WHERE ([Extent1].[Key] = @p__linq__0) 
        AND (( CAST( [Extent1].[Value] AS int) < @p__linq__1) 
          OR ( CAST( [Extent1].[Value] AS int) > @p__linq__2))
    )  AS [GroupBy1]