How do I extend ADO.NET Entity Framework objects with partial classes?

Question

I've created a Visual Basic WPF Application project that contains Toy.edmx, an ADO.NET Entity Data Model generated from a database called Toy.

Its Window1.xaml.vb file looks like this:

1   Class Window1
2   
3       Private Sub Window1_Loaded( _
4       ByVal sender As System.Object, _
5       ByVal e As System.Windows.RoutedEventArgs) _
6       Handles MyBase.Loaded
7   
8           Dim dc As New ToyEntities1
9           Label1.Content = (From c As Client In dc.ClientSet _
10                            Select c).First.FirstName
11  
12      End Sub
13  
14  End Class

That runs just fine.

But, if I add the file Client.vb...

1   Partial Public Class Client
2       Function IsWashington() As Boolean
3           Return Me.LastName = "Washington"
4       End Function
5   End Class

...and add a WHERE clause to my Window1.xaml.vb query...

9           Label1.Content = (From c As Client In dc.ClientSet _
10                            Where c.IsWashington _
11                            Select c).First.FirstName

...then I get this NotSupportedException:

LINQ to Entities does not recognize the method 'Boolean IsWashington()' method, and this method cannot be translated into a store expression.

How do I extend ADO.NET Entity Framework objects with partial classes?

Answer 1

What type is Client class?

You might need to add namespace (same as that in which Client "Entity classs" is defined) to the file containing "IsWashington".

Answer 2

The problem is that you're writing code, and expecting the Entity Framework to translate that into SQL... it can't do that. Just like LINQ to SQL can't do that.

Imagine if your property read a file from the "C:\" drive... how do you think it would handle that? - not possible.

Answer 3

Is this what you're trying to do - create a method that applies a filter to Client queries.

I don't know vb.net, so don't trust this free-hand code 100%.

Partial Public Class Client
  Public Shared Function IsWashington(query As IQueryable(Of Client)) As IQueryable(Of Client)
    Return query.Where(Function(someClient) someClient.LastName = "Washington")
  End Function
End Class

later, some calling code.

IQueryable(Of Client) someQuery = dc.ClientSet.AsQueryable
someQuery = Client.IsWashington(someQuery)

Label1.Content = someQuery.First.FirstName

Hope this works!

Answer 4

You could work around this particular problem by feeding your Client object from a View. Use the SQL CASE statement to set a bit column value:

SELECT col1, col2, col3, LastName CASE LastName WHEN 'Washington' THEN 1 ELSE 0 AS IsWashington FROM Client

If you use the view as the basis for your Client entity object, the IsWashington column should become a member of the class along with all the other columns.

Answer 5

shahkalpesh is correct, you need to add the namespace around your extended class to match the generated one.