Problem with using Join operator in Lambda Expression and Expression Tree

Question

I write this method:

public List<TResult2> SelectAndJoin<TOuter, TInner, TKey, TResult, TResult2>(IEnumerable<TInner> inner, 
                                                                      System.Linq.Expressions.Expression<Func<Regions, TKey>> outerKeySelector, 
                                                                      System.Linq.Expressions.Expression<Func<TInner, TKey>> innerKeySelector, 
                                                                      System.Linq.Expressions.Expression<Func<Regions, TInner, TResult>> resultSelector,
                                                                      Func<Regions, TResult2> selector)
    {
        using (RepositoryDataContext = new DataClasses1DataContext())
        {
                return RepositoryDataContext.Regions.Join(inner, outerKeySelector, innerKeySelector, resultSelector).AsEnumerable<TResult2>().Select<Regions, TResult2>(selector).ToList<TResult2>();

        }
    }

but the expression follow return has this Error:

'System.Linq.IQueryable' does not contain a definition for 'AsEnumerable' and the best extension method overload 'System.Linq.Enumerable.AsEnumerable(System.Collections.Generic.IEnumerable)' has some invalid arguments

How I can get rid of this error?

is this code standard?

thanks

Snowbear · Accepted Answer · 2011-04-30 21:15:16Z

2

You're calling AsEnumerable<TResult2> on enumerable which will be of type IQueryable<TResult>. You should call AsEnumerable<TResult> or you can even omit generic parameter and call AsEnumerable()

Also your next select will not work for the same reason - you are providing wrong types for generics.

answered Apr 30, 2011 at 21:15

Snowbear

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Comments

Stuart · Accepted Answer · 2011-04-30 21:01:24Z

0

I might be missing the point... but:

IQueryable inherits from IEnumerable so I think that AsEnumerable() is unnecessary in this code.

If you really do need/want to execute the query before doing the Select, then you could use ToList() instead of AsEnumerable() - this would be clearer

I'm also wondering if you are including using System.Linq in your .cs file - as AsEnumerable() is an extension method within System.Linq

answered Apr 30, 2011 at 21:01

Stuart

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3 Comments

BrokenGlass Over a year ago

AsEnumerable() is a neccessary step to be able to do Linq to Objects queries on top of a Linq to Entities/SQL query

Snowbear Over a year ago

This is not about using, he would have different error in that case.

DooDoo Over a year ago

I think the point is Join return a custom projection and it must be AsEnumerable<TResult>().I must test it and write here the result.

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