Linq to EF Join throws "Index was out of range" after upgrade from VS2010 to VS2012

Question

After upgrading from Visual Studio 2010 to 2012 code started throwing "ArgumentOutOfRangeException - Index was out of range. Must be non-negative and less than the size of the collection.Parameter name: index" on Linq queries using Joins.

The following simple example made in LINQPad (using an EF data model) gives me the ArgumentOutOfRangeException:

void Main()
{
    var iq1 = Customers.Select(ap => ap.ID);
    var iq2 = iq1.Join(Customers.Select(ap => ap.ID),
                    a => a,
                    b => b,
                    (a, b) => new { a });

    iq2.Dump(); 
}

Changing the previous example to return an anonymous object containing both sides of the join doesn't give the ArgumentOutOfRangeException and gives results as expected:

void Main()
{
    var iq1 = ActionPlans.Select(ap => ap.ID);
    var iq2 = iq1.Join(ActionPlans.Select(ap => ap.ID),
                    a => a,
                    b => b,
                    (a, b) => new { a, b });

    iq2.Dump(); 
}

Ok, so for some reason I had to return both sides of the join, but then I tried the following example using a dummy value instead, that also executed without a problem:

void Main()
{
    var iq1 = ActionPlans.Select(ap => ap.ID);
    var iq2 = iq1.Join(ActionPlans.Select(ap => ap.ID),
                    a => a,
                    b => b,
                    (a, b) => new { a, x = 1 });

    iq2.Dump(); 
} 

Taking the first example and adding a ToList() to the first query also makes it execute without a problem:

void Main()
{
    var iq1 = ActionPlans.Select(ap => ap.ID).ToList();
    var iq2 = iq1.Join(ActionPlans.Select(ap => ap.ID),
                    a => a,
                    b => b,
                    (a, b) => new { a });

    iq2.Dump(); 
}

Important: Trying the first query on a workstation without the Visual Studio 2012 upgrade works fine!

Can anyone confirm/explain this new "feature"? :-)

Answer 1

Erwin, just to close the loop on this: We have confirmed that it is a bug we introduced recently in LINQ to Entities and we are looking at ways to get a fix out. Thanks a lot for reporting it!

Answer 2

After giving this some more investigation, I've come to the conclusion that the problem is the anonymous class I'm returning from the Linq query, I think it isn't allowed anymore to return an anonymous class with only one field in it, I know it isn't needed to wrap the field in an anonymous class but ... as I said this worked before upgrading.

Following example gives me the "ArgumentOutOfRangeException - Index was out of range":

void Main()
{
    var iq1 = ActionPlans.Select(ap => ap.ID).ToList();
    var iq2 = iq1.Join(ActionPlans.Select(ap => ap.ID),
                    a => a,
                    b => b,
                    (a, b) => new { a });

    iq2.Dump();
}

this next example works as expected:

void Main()
{
    var iq1 = ActionPlans.Select(ap => ap.ID).ToList();
    var iq2 = iq1.Join(ActionPlans.Select(ap => ap.ID),
                    a => a,
                    b => b,
                    (a, b) => a );

    iq2.Dump();
}