I've got a DBQuery<T> which converts to an IQueryable<T> (this bit works fine). But then I'm trying to convert the IQueryable to an ObjectQuery .. which fails :-
public void Foo(this IQueryable<T> source)
{
// ... snip ...
ObjectQuery<T> objectQuery = source as ObjectQuery<T>;
if (objectQuery != null)
{
// ... do stuff ...
}
}
This used to work before I changed over to Entity-Framework 4 CTP5 Magic Unicorn blah blah blah. Now, it's not working - ie. objectQuery is null.
Now, DBQuery<T> inherits IQueryable<T> .. so I thought this should work.
If i change the code to ..
var x = (ObjectQuery<T>) source;
then the following exception is thrown :-
System.InvalidCastException: Unable to cast object of type 'System.Data.Entity.Infrastructure.DbQuery
1[Tests.Models.Order]' to type 'System.Data.Objects.ObjectQuery1[Tests.Models.Order]'.
Any suggestions?
DbQuery<T> contains Include method so you don't need to convert to ObjectQuery. ObjectQuery is not accessible from DbQuery instance - it is wrapped in internal type InternalQuery and conversion operator is not defined.
Btw. when you add using System.Data.Entity and refrence CTP5 you will be able to call Include on IQueryable<T>!
Using reflection, you can do this:
var dbQuery = ...;
var internalQueryField = dbQuery.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Instance).FirstOrDefault(f => f.Name.Equals("_internalQuery"));
var internalQuery = internalQueryField.GetValue(dbQuery);
var objectQueryField = internalQuery.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Instance).FirstOrDefault(f => f.Name.Equals("_objectQuery"));
// Here's your ObjectQuery!
var objectQuery = objectQueryField.GetValue(internalQuery) as ObjectQuery<T>;
Not sure what you're trying to do with it, but would a dynamic variable help?
来源：https://stackoverflow.com/questions/4766122/how-can-i-convert-a-dbqueryt-to-an-objectqueryt