.distinct not working

[Markus]

Good day all

I am trying to create a pulldown with all distinct cities from a table. I use this code below.

Any idea why the .Distinct() is not having any effect, and how I would have to create the statement?

(I am NOT getting an error. Simply all cities  not filtered distinct)

using (EntitiesModel dbContext = new EntitiesModel())
               {
                   List<T_user> FirmenNachOrt = (from a in dbContext.T_users
                                                 where a.User_benutzung == "Firma" && a.User_freischaltung == false
                                                 orderby a.User_ort
                                                     select  a).Distinct().ToList();
                   rddl_firmen_nach_ort.DataSource = FirmenNachOrt;
                   rddl_firmen_nach_ort.DataTextField = "user_ort";
                   rddl_firmen_nach_ort.DataValueField = "user_ort";
                   rddl_firmen_nach_ort.DataBind();
                   rddl_firmen_nach_ort.Items.Insert(0, new DropDownListItem("Nach Ort suchen"));

               }

Markus

[Viktor Zhivkov]

Hi Markus,

OpenAccess LINQ supports Distinct on the database server side only if you are doing it by a primitive property bound to a database column. If you are doing distinct by the whole entity object it will be done in-memory using .Net comparison rules.

If you want to get only the distinct values from T_users.User_ort you should modify your query slightly:

01.using (EntitiesModel dbContext = new EntitiesModel())
02.{
03.    List<string> FirmenNachOrt = (from a in dbContext.T_users
04.                 where a.User_benutzung == "Firma" && a.User_freischaltung == false
05.                 orderby a.User_ort
06.                 select  a.User_ort).Distinct().ToList();
07.
08.    // TODO: bind the combobox properly to the new List<string>
09.}

If you need the whole T_users object, please implement a custom IEqualityComparer<T_users> and provide it as parameter of the Distinct method call. You should note that the filter will be applied in-memory and you will fetch some unnecessary data from the database.

If you need any further assistance do not hesitate to contact us again.

Regards,
Viktor Zhivkov
Telerik

[Ru'a]

finally,,,,
thux