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[Solved] .distinct not working

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LINQ (LINQ specific questions)

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Markus asked on 03 Jun 2013, 09:51 AM

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

2 Answers, 1 is accepted

answered on 03 Jun 2013, 01:27 PM

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

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