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();
}
}
