Question

I have a class ApprovalTicket that has a property called ApprovalRules that is of type IApproval:

IApproval ApprovalRules;

This field will contain several different types of classes that implement that interface. Now stepping one level up, I will have a List of ApprovalTickets. What I’m trying to do is use linq to return a list of ApprovalTickets that have ApprovalRules of the type MocReviewerApproval.

I was trying something like:

var reviews = request.MocApprovalTasks
  .Where(mocApproval => mocApproval.ApprovalRules is MocReviewerApproval)
  .ToList();

But when I check the list that gets returned, it’s still including tickets that have an ApprovalRules type of MocManagerApproval and others as well. What am I missing?

UPDATE:

Let me be more specific. Here is the inheritance scheme

MocApproval : TaskTicket
    >>IApproval ApprovalRules;

MocReviewerApproval : IApproval
MocManagerApproval : IApproval
MocControllerApproval : IApproval


    internal interface IApproval
    {
        bool Approve(Guid approverGuid, MocApproval approval);
        bool Deny(Guid approverGuid, MocApproval approval, TaskComment denialComment);
        bool Close(Guid approverGuid, MocApproval approval, TaskComment closeComment);
        bool Notify();
        void Set(MocApproval approval);
        User GetAssignee();
        TaskComment GetNotificationComment();
    }

Answer 1

Your code looks fine to me. I suspect you’ve got diagnostic problems, or you’re not after the is kind of relationship at all. Here’s a complete example showing it working:

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

class Foo
{
    public object Value { get; set; }
}

class Test
{
    static void Main()
    {
        var list = new List<Foo>
        {
            new Foo { Value = "" },
            new Foo { Value = 10 },
            new Foo { Value = new object() },
            new Foo { Value = new MemoryStream() }
        };

        ShowCount<IDisposable>(list); // 1 (MemoryStream)
        ShowCount<IFormattable>(list); // 1 (Int32)
        ShowCount<IComparable>(list); // 1 (String, Int32)
    }

    static void ShowCount<T>(List<Foo> list)
    {
        var matches = list.Where(f => f.Value is T)
                          .ToList();
        Console.WriteLine("{0} matches for {1}", 
                          matches.Count, typeof(T));
    }
}

EDIT: If you want matches which are exactly the given type, use:

var reviews = request.MocApprovalTasks
                     .Where(task => task.ApprovalRules.GetType() == 
                                           typeof(MocReviewerApproval))
                     .ToList();

That’s more refactoring-friendly than finding the name as per Servy’s original answer.