Question

I’m new to WCF data services. I have a quite simple data model. Some of its properties have the same type, like this:

public IQueryable<IntegerSum> HouseholdGoodsSums
{
    get
    {
        return GetData<IntegerSum>(DefaultProgramID, "rHouseholdGoodsPrice", IntegerSumConverter);
    }
}

public IQueryable<IntegerSum> StructureSums
{
    get
    {
        return GetData<IntegerSum>(DefaultProgramID, "rStructurePrice", IntegerSumConverter);
    }
}

The IntegerSum is a very very simple class:

[DataServiceKey("Amount")]
public class IntegerSum
{
    public int Amount { get; set; }
}

When I navigate to my service in a web browser, I see the following error message:

The server encountered an error processing the request. The exception message is ‘Property ‘HouseholdGoodsSums’ and ‘StructureSums’ are IQueryable of types ‘IntegrationServices.PropertyIntegrationServices.IntegerSum’ and ‘IntegrationServices.PropertyIntegrationServices.IntegerSum’ and type ‘IntegrationServices.PropertyIntegrationServices.IntegerSum’ is an ancestor for type ‘IntegrationServices.PropertyIntegrationServices.IntegerSum’. Please make sure that there is only one IQueryable property for each type hierarchy.’.

When I get rid of one of these two properties, the service starts working.

I searched for this error message in google, but haven’t found a solution.
Is it really not allowed to have two properties with the same type in a data model? If so, why?

Answer 1

Comrade,

To address the error first, you’re running into a limitation in the Reflection provider. Specifically, the Reflection provider doesn’t support MEST.

That said, there are better approaches to achieve what you’re trying to achieve. You should probably not make IntegerSum an entity type (an entity type is a uniquely identifiable entity, which doesn’t really fit your scenario). While you can’t expose that directly, you can expose it as a service operation. That seems much closer to what you’re trying to achieve.

A couple of ways to distinguish between whether or not something should be an entity:

1. If it has a key already, such as a PK in a database, it should probably be an entity type
2. If you need to create/update/delete the object independently, it must be an entity type

HTH,
Mark