LINQ - Distinct() not working as expected

Issue: 

When using custom classes not generated by LINQ to SQL, Distinct() is unable to determine that two objects might be the same based on a key or all values within the objects, and simply sees two different objects regardless.

Solution:

Distinct() has an overload which takes an IEqualityComparer, thus allowing you to specify the value or values in which to compare and determine uniqueness upon.

Ex: For simplicity, lets say the list of clients passed in has duplicates. OID is organization id, and CID is client id.

            public static IEnumerable<CustomClient> GetClientsByOrganizationID(IEnumerable<CustomClient> clients, int oid)

            {

                using (DataContext db = new DataContext())

                {

                    db.DeferredLoadingEnabled = false;

                    var query = from c in clients

                                join o in db.Organizations on c.OID equals o.OID

                                where o.OID == oid

                                select c;

                    return query.Distinct(new ClientComparer()).ToList();

                }

            }

            public class ClientComparer : IEqualityComparer<CustomClient>

            {

                public bool Equals(CustomClient x, CustomClient y)

                {

                    return x.CID == y.CID;

                }

                public int GetHashCode(CustomClient obj)

                {

                    return obj.CID.GetHashCode();

                }

            }