R – How to use Read-Only properties defined in partial (Entity Framework) classes over ADO.Net Data Services

entity-frameworknetpartial-classeswcf-data-services

I have objects that are defined by the Entity Framework that I have then added additional methods and properties to via partial classes. I think I understand most of the limitations around doing this, but wanted to confirm something I am seeing (or hopefully learn what I need to do to make this work).

I have a partial class that then has a read-only property that uses a couple of the items to create a calculated field that is read-only. It was curious to see that read-only property did not come back via the ADO.Net Data Services as I was hoping/expecting. i.e. I was expecting to see the properties on the entity framework and the property being definied in code via the partial class come via the Data Service call.

Is this the case? Are the partial classes completely ignored when ADO.Net Data Services is querying for data? If so what is the best practice for getting a read-only type property onto an entity (as I would like to avoid having the same partial classes with different namespaces being cut and pasted into both the client side and server side code bases).

Best Answer

From a Microsoft Forums Post: (see full post here)

"I think you are asking "How to add a read-only property to an existing entity that is exposed by the EF provider"? In V1, there is no good way to do this. For EF, we load the metadata using the EF metadata api's and hence we don't do any reflection. Hence additional properties that you might have added via a partial class will get ignored.

Astoria doesn't yet have a concept of read-only properties. So if we expose any other properties that is not part of the model, we don't know how to deal with them in updates. We don't want to lose data siliently in the server also."

So it looks like this is functionality that is not able to be exposed via ADO.Net Data Services.

Related Solutions

.net – How to extend ADO.NET Entity Framework objects with partial classes

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!

R – How to put business logic in the ADO.NET Entity Framework classes

You can architect your solution using (Plain Old C# Objects) POCO's and Managers.

That way you separate the business logic from the value objects.

To make it "look pretty", you can mark your methods with the (this) modifier on the parameters so you can then use those methods as extension methods.

An example could make this pretty clear:

Location Value Object:

public class Location
{
    public string City { get; set; }
    public string State { get; set; }
}

Location Manager:

public static class LocationManager
{
    public static bool IsWashington(this Location location)
    {
        return location.State == "WA";
    }
}

Now, the extension methods will show up differently than the standard properties/methods on the object.

The "IsWashington" method can be called 2 ways

Location location = new Location { State = "WA" };
LocationManager.IsWashington(location);

OR

Location location = new Location { State = "WA" };
location.IsWashington();

Now you have separation of your business logic and value objects, yet you still can have "pretty" method calls.

If you feel your fellow devs (or you :) ) will abuse the extension method part, then just don't use it.