“The LINQ expression node type ‘Invoke’ is not supported in LINQ to Entities” – stumped!

In my EF later, I’m trying to pass in an anonymous function to be used as part of my Linq query. The function would pass in an INT and return a BOOL (u.RelationTypeId is an INT). Below is a simplified version of my function:

public IEnumerable<UserBandRelation> GetBandRelationsByUser(Func<int, bool> relation)
{
    using (var ctx = new OpenGroovesEntities())
    {
        Expression<Func<UsersBand, bool>> predicate = (u) => relation(u.RelationTypeId);

        var relations = ctx.UsersBands.Where(predicate);

        // mapping, other stuff, back to business layer
        return relations.ToList();
    }
}

However, I get the error stated above. It seems like I’m going everything correct by building a predicate from the function. Any ideas? Thanks.

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

I was getting this very error and I’m using Entity Framework with PredicateBuilder by Joe Albahari to build dynamic where clauses. If you happen to be in the same condition, you should call the AsExpandable method:

If querying with Entity Framework, change the last line to this:

return objectContext.Products.AsExpandable().Where(predicate);

This method is part of LINQKIT DLL that you can grab here or through a NuGet package here.

Everything works fine now. 🙂

Method 2

You’re trying to pass an arbitrary .NET function in… how could the entity framework hope to translate that into SQL? You can change it to take an Expression<Func<int, bool>> instead, and build the Where clause from that, although it won’t be particularly easy, because you’ll need to rewrite the expression with a different parameter expression (i.e. replacing whatever parameter expression is in the original expression tree with the expression of calling u.RelationTypeId).

To be honest, for the sake of just specifying u.RelationTypeId in the lambda expression that you use to create the expression tree to pass into the method, you’d be better off just using:

public IEnumerable<UserBandRelation> GetBandRelationsByUser(
    Expression<Func<UsersBand, bool>> predicate)
{
    using (var ctx = new OpenGroovesEntities())
    {
        var relations = ctx.UsersBands.Where(predicate);

        // mapping, other stuff, back to business layer
        return relations.ToList();
    }
}

Method 3

You can call the Expand() method on your predicate before the Where request.

Method 4

I know this answer is really late, but I ran into the same problem and it led me here, so I thought I’d share my solution.

I read Leniel’s answer, and it gave me an idea. The default types have the method “AsEnumerable()” which behaves the same way, alleviating the issue.


All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

0 0 votes
Article Rating
Subscribe
Notify of
guest

0 Comments
Inline Feedbacks
View all comments
0
Would love your thoughts, please comment.x
()
x