Collections with user defined class - find differences

Question

This is my model:

public class EventModel
{
    public DateTime? EVENT_DATE { get; set; }
    public decimal? EVENT_TYPE { get; set; }
    public string EVENT_DESCRIPTION { get; set; }
}

I fill this class into ObservableCollection<EventModel>. When I do that, I also deep-copy same collection. Then I want to compare these two collections in later use.

I would preferably use LINQ to do that, with something like

bool are_same = collection1.OrderBy(i => i).SequenceEqual(
                 collection2.OrderBy(i => i));

This means that both collections needs to be sorted and then compared to each other for finding differencies in ALL PROPERTIES.

There are a lot of examples for implementing IComparable & IEqualityComparer, but I'm confused about what I need and how.

I would appreciate If someone would show me how this can be done in C#.

Answer 1

If you simply want to check if the two collections are equal you need to define what equality is, for example by implementing IEqualityComparer<T>. This can also be done by implementing IEquatable<T> or or by overriding Equals(object) and GetHasCode. This can be done automatically by some refactoring tools:

public sealed class EventModelEqualityComparer : IEqualityComparer<EventModel>
    {
        public bool Equals(EventModel x, EventModel y)
        {
            if (ReferenceEquals(x, y)) return true;
            if (ReferenceEquals(x, null)) return false;
            if (ReferenceEquals(y, null)) return false;
            if (x.GetType() != y.GetType()) return false;
            return Nullable.Equals(x.EVENT_DATE, y.EVENT_DATE) &&
                   x.EVENT_TYPE == y.EVENT_TYPE &&
                   x.EVENT_DESCRIPTION == y.EVENT_DESCRIPTION;
        }

        public int GetHashCode(EventModel obj)
        {
            unchecked
            {
                var hashCode = obj.EVENT_DATE.GetHashCode();
                hashCode = (hashCode * 397) ^ obj.EVENT_TYPE.GetHashCode();
                hashCode = (hashCode * 397) ^ (obj.EVENT_DESCRIPTION != null ? obj.EVENT_DESCRIPTION.GetHashCode() : 0);
                return hashCode;
            }
        }
    }

To compare two collections to see if they contains the same items, but in arbitrary positions, you can use a HashSet.SetEquals:

myCollection.ToHashSet(new EventModelEqualityComparer()).SetEquals(myOtherCollection);