Question

I don’t see what I’m doing wrong with the LINQ query below.

I’m building a generic type:

public class MyClass<TKey, TValue> : IList<TValue> { ... }

Within this class I declare a nested private type:

private class Pair {
    public TKey Key { get; set; }
    public TValue Value { get; set; }

    public Pair() {
        Key = default( TKey );
        Value = default( TValue );
    }
}

So far so good. Now, in MyClass I have a method which has an array of TKey objects. I want to use LINQ to extract a page of TKey objects and create a smaller array of Pair objects. Here’s the query I’ve built:

TKey[] Keys = ...;
IQueryable<Pair> query = from key in Keys
                         select new Pair { Key = key, Value = default( TValue ) };

When I compile the program, I get the following error on the line with the select in it:

Cannot implicitly convert type 
    'System.Collections.Generic.IEnumerable<MyNameSpace.MyClass<TKey,TValue>.Pair>'
to  'System.Linq.IQueryable<VirtualLoadApp.MyClass<TKey,TValue>.Pair>'. 
An explicit conversion exists (are you missing a cast?)

What am I doing wrong?

Tony

Answer 1

Try this:

            var q = from key in Keys
                    select (new Pair { Key = key, Value = default(TValue) });
            IQueryable<Pair> query = q.AsQueryable<Pair>();