One context reference LINQ query throws multiple references exception - BUG?

Question

I'm using the following code:

using(MainEntities mainContext = new MainEntities())
{
    return (from member in mainContext.aspnet_Membership
            where adminGroupUserIDs.Contains(member.UserId)
            select new
            {
                FullName = member.FirstName + " " + member.LastName,
                UserName = (from user in mainContext.aspnet_Users
                            where user.UserId == member.UserId
                            select user.UserName)
            }).ToList(); 
}

where adminGroupUserIDs is an IQueryable<GUID> that is formed from a query to a different instance of MainEntities.

With this query LINQ complains that:

The specified LINQ expression contains references to queries that are associated with different contexts.

Any ideas why?

I'm not sure what is going on in the background, but maybe you need to create another instance of MainEntities to use in the inner expression (`from user in mainContext.aspnet_Users ...`) - see http://stackoverflow.com/questions/7332920/the-specified-linq-expression-contains-references-to-queries-that-are-associated — PzYon, Oct 22 '14 at 21:53
@Pzyon: Quite the opposite. If he did, then he would definitely get that error. — Allon Guralnek, Oct 23 '14 at 08:03

score 4 · Accepted Answer · answered Oct 23 '14 at 07:56

4

I can't be certain from the code you show here, but I'm pretty sure that adminGroupUserIDs is the result of another query that hasn't been retrieved yet, and was created with a different instance of MainEntities. You can't mix queries from different contexts, not even different instances of the same context class. Try changing it to the following:

var loadedAdminGroupUserIDs = adminGroupUserID.ToArray();

using(MainEntities mainContext = new MainEntities())
{
    return (from member in mainContext.aspnet_Membership
            where loadedAdminGroupUserIDs.Contains(member.UserId)
            select new
            {
                FullName = member.FirstName + " " + member.LastName,
                UserName = (from user in mainContext.aspnet_Users
                            where user.UserId == member.UserId
                            select user.UserName)
            }).ToList(); 
}

answered Oct 23 '14 at 07:56

Allon Guralnek

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Excellent point Allon. I totally overlooked `adminGroupUserIDs`! Originally the query I posted built the query using the repositories in the Repository Pattern fashion, i.e. using `MembershipRepository.All` and `UsersRepository.All`. But then I got the error I posted above and switched to a `using` block. But I think you nailed it, because `adminGroupUserIDs` is and IQueryable being built by a third repository! – seebiscuit Oct 23 '14 at 13:42
The problem with your fix is that `loadeAdminGroupUserIDs` is now in-memory, and I'm bound to get a `Unable to create a constant value of type` error, since the query is in the DB. At the end I had to go with a join, which is probably closer to native SQL. But still I was sure that I could've implemented your solution. What was I missing? – seebiscuit Oct 23 '14 at 13:46
Another point. I tripped myself up because I wanted to build my query from my repositories, each of which represents a table. With this pattern, each Repo will instantiate a `MainEntities` context. Gleaning from this case, can I infer that the Repo pattern is only useful when performing queries on only ONE table? Am I implementing the pattern incorrectly? This may be another SO question. – seebiscuit Oct 23 '14 at 13:52
Assuming `adminGroupUserIDs` is an `IQueryable` (or ``), my suggestion above would cause Entity Framework to convert the `.Contains(...)` into an `IN` expression, so that if `adminGroupUserIDs` contained three IDs, 5, 18 and 42, an in-memory array of these three values would be created by the first line, then EF would recognize this and create the following SQL: `WHERE UserId IN (5, 18, 42)`, which would also work without using a single data context. But if you want all of this to happen inside the database, then you have to use a single data context (with or without a join). – Allon Guralnek Oct 23 '14 at 14:05
I'm sorry, Allon, I missed a material point. `adminGroupUserIDs` is a GUID :(. Which explains why the `.Contains` failed. Thanks for the insight. Will edit my question. – seebiscuit Oct 23 '14 at 14:15
@Seabiscuit: Entity Framework (4.0 and above) supports `.Contains()` on most SQL primitives, including GUIDs. So it should work even on an `Guid[]` or `IEnumerable` (but not `IQueryable`). – Allon Guralnek Oct 24 '14 at 15:09

score 0 · Answer 2 · answered Oct 23 '14 at 07:58

0

Try adding .FirstOrDefault() to your subquery.

using(MainEntities mainContext = new MainEntities())
{
    return (from member in mainContext.aspnet_Membership
            where adminGroupUserIDs.Contains(member.UserId)
            select new
            {
                FullName = member.FirstName + " " + member.LastName,
                UserName = (from user in mainContext.aspnet_Users
                            where user.UserId == member.UserId
                            select user.UserName).FirstOrDefault()
            }).ToList(); 
}

answered Oct 23 '14 at 07:58

serdar

1,564
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Yes, this is another mistake in the query, good catch! Although I don't see how it would cause the above error. – Allon Guralnek Oct 23 '14 at 08:00
1

Good catch. Unfortunately, the problem was exactly what @AllonGuralnek suggested, I included 3! different `MainEntity` contexts in my query (2 in the query itself, and `adminGroupUserIDs` was an IQueryable from a third `MainEntities` context). That's sort of the reality of using the Repository Pattern. I required 3 different repositories, each of which instantiated a `MainEntities` context. – seebiscuit Oct 23 '14 at 13:49

One context reference LINQ query throws multiple references exception - BUG?

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