Closed Issue: MustFix: Linq to EF Join throws “Index was out of range” after upgrade from VS2010 to VS2012 [563]

Tracking of an issue reported in StackOverflow: http://stackoverflow.com/questions/12489749/linq-to-ef-join-throws-index-was-out-of-range-after-upgrade-from-vs2010-to-vs2

There's an easy workaround, but this is a functional regression.

Copying the contents of the original StackOverflow 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"? :-)



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();
}
Comments: Changeset 0eed9c4e9ebe