查询结果不能被多次枚举。

Question

I have a listview dialog to bind a data to that listview.

private void BindListView(string DCLookupMstr_Value, int reportCatId, string DCLookup_Value = null)

    {          

         using (Model.OperationalAnalyticsEntities oadb = new Model.OperationalAnalyticsEntities())
            {
                var res = oadb.prGetDailyCensusLookup(DCLookupMstr_Value, reportCatId, DCLookup_Value);
                Session["LookupValues"] = res;
                lvLookup.DataSource = res.ToList();
                lvLookup.DataBind();
            }            
    }

And I put a search box(textbox) on that listview dialog. If user type any text/chars, using linq query..populate the listview again with the values which contains given chars. My code is below

protected void txtSearch_TextChanged(object sender, EventArgs e)
    {
        var text = txtSearch.Text;
        //var list = new List<Model.prGetDailyCensusLookup_Result>();
        var lookUpValue = Session["LookupValues"] as ObjectResult<Model.prGetDailyCensusLookup_Result>;
        var list = lookUpValue.Where(x => x.DCLookup_Value.Contains(text));

        lvLookup.DataSource = list.ToList();
        lvLookup.DataBind();  
     }

I am getting the "result of a query cannot be enumerated more than once" where ever i added .ToList(). I am not sure what did I miss.

Please Help!

Answer 1

In BindListView , when you do .ToList() , it enumerates the query for the first time. And what you store in the session is the query itself. When you do .ToList() again in txtSearch_TextChanged , it enumerates the query a second time, which is not supported.

You should store the result of .ToList() in the session, rather than the query:

Session["LookupValues"] = lvLookup.DataSource = res.ToList();

Answer 2

You value you are storing in Session is the LINQ query, not the result of the query. The second time it is used (the list.ToList() ) it throws this error.

This is easily fixed by storing the result as a list in Session instead.

var res = oadb.prGetDailyCensusLookup(DCLookupMstr_Value, reportCatId, DCLookup_Value)
              .ToList();
Session["LookupValues"] = res;
lvLookup.DataSource = res;
lvLookup.DataBind();