Weird exception when I use LINQ

Question

I use piece of code as following:

list.OrderByDescending(x => x.Supporters.Sum(y=>y.Tokens));

(short explanation: any x has list of Supporters,any Supporter can give some tokens, I need to order x by sum of token).

and I got an exeption:

Unable to cast object of type 'System.Linq.Expressions.MethodCallExpressionN' to type 'System.Linq.Expressions.MemberExpression'."} System.SystemException {System.InvalidCastException}

What's wrong and how to make it correct? Thanks for help.

Answer 1

Without seeing the rest of your code it's a bit tricky. I just tried it for myself (see code below) and I didn't get any problems.

Here's my code:

static void Main(string[] args)
{
    List<Team> list = new List<Team>
        {
            new Team { Name = "1", Supporters = new List<Supporter>
                {
                    new Supporter { Name = "Bob", Tokens = 4 },
                    new Supporter { Name = "Sarah", Tokens = 3 },
                    new Supporter { Name = "Jane", Tokens = 6 },
                } },
            new Team { Name = "2", Supporters = new List<Supporter>
                {
                    new Supporter { Name = "Brian", Tokens = 4 },
                    new Supporter { Name = "Ellie", Tokens = 19 },
                    new Supporter { Name = "Steve", Tokens = 12 },
                } },
            new Team { Name = "3", Supporters = new List<Supporter>
                {
                    new Supporter { Name = "John", Tokens = 7 },
                    new Supporter { Name = "Vern", Tokens = 11 },
                    new Supporter { Name = "Peter", Tokens = 18 },
                } },
        };

        var results = list.OrderByDescending(x => x.Supporters.Sum(y => y.Tokens));
    }
}

class Team
{
    public string Name { get; set; }

    public List<Supporter> Supporters { get; set; }
}

class Supporter
{
    public string Name { get; set; }

    public int Tokens { get; set; }
}

Answer 2

The Tokens property on the Supporter object is an int or a collection of something? Because if it's an int it should work fine, in the other case you should do:

list.OrderByDescending(x => x.Supporters.Sum(y=>y.Tokens.Count()));