无法使用IQueryable在LINQ中进行强制转换？

Question

I'm wondering how to get the query below to work:

IQueryable<TypeA> data  = ...;                  
data = data.OrderBy(x => ((TypeB)x.RelatedObject).Value);

The error I get is:

The specified type member 'RelatedObject' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.

I'm very new to C#, I think this is a compile problem because I know RelatedObject is of TypeB . Thanks!

Answer 1

Apparently, Entity Framework does not know (enough) about the relation between TypeA and TypeB. If you can define it as a navigation property , that would solve your problem.

If that is not possible, inserting .AsEnumerable() should work:

data.AsEnumerable().OrderBy(x => ((TypeB)x.RelatedObject).Value);

What this will do, is having 'normal' LINQ performing the ordering, instead of the database (with an ORDER BY clause in the SQL query). Note that it returns an IEnumerable<TypeA> instead of an IQueryable<TypeA> - depending on what you do with this variable, this might cause more records to be loaded into memory than strictly necessary.

Answer 2

If you know that you're only getting one specific type, you should be able to do something like this, assuming that EF knows about the inheritance.

IQueryable<TypeA> data  = ...;                  
data = data.OfType<TypeB>().OrderBy(x => (x.RelatedObject).Value);