Use of “Single” in Dynamic Linq

Question

I am trying to convert a Linq query that I have working in Linq to be able to work in dynamic linq (using System.Linq.Dynamic) because I want a user to be able to form their

Answer 1

Get the source of Linq.Dynamic, copy paste the Where method, change the signature and the string with the function name inside the method and you're good to go. I did it to add Single First etc, I can't copy it here because I'm not on my dev machine but I'll do it later if necessary ;)

EDIT: here's the Single method if you decide to use it:

public static object Single(this IQueryable source)
    {
        if (source == null) throw new ArgumentNullException("source");
        return source.Provider.Execute(
            Expression.Call(
                typeof(Queryable), "Single",
                new Type[] { source.ElementType },
                source.Expression));
    }

Answer 2

Sorry to digg up a very old thread, but I thought I could add somevaluable information!

I had to do this for First()/FirstOrDefault() with Linq to Entities instead of your Linq to SQL and I can confirm @Guillaume86 's solution sure works!

Here's how I modified MicrosoftDynamic.sql: I added this inside the static DynamicQueryable class:

    public static object FirstOrDefault(this IQueryable source)
        {
            if (source == null) throw new ArgumentNullException("source");
            return source.Provider.Execute(
                Expression.Call(
                    typeof(Queryable), "FirstOrDefault ",
                    new Type[] { source.ElementType },
                    source.Expression));
        }

I also modified interface IEnumerableSignatures as

            void FirstOrDefault();

(I used FirstOrDefault because First() isn't supported when it's not the last call in linq to entities)

You can repeat this for any supported function :)