Avoid Multiple time Submit button click event

<asp:Button ID="btnSubmit" runat="server" class="btn btn-success"  OnClick="btnSubmit_Click"
                      ValidationGroup="Submit" Text="Submit" OnClientClick="if (!Page_ClientValidate()){ return false; } this.disabled = true; this.value = 'Saving...';"
   UseSubmitBehavior="false"></asp:Button>

Entity Framework with LINQ aggregate to concatenate string

DataTypeID, Name, DataValue
1,"Data 1","Value1"
1,"Data 1","Value2"
2,"Data 1","Value3"
3,"Data 1","Value4"


var query = (from t in context.TestData
group t by new { DataTypeID = t.DataTypeID, Name = t.Name } into g
select new { DataTypeID = g.Key.DataTypeID, Name = g.Key.Name, Data = g.AsEnumerable()})
.ToList()
.Select (q => new { DataTypeID = q.DataTypeID, Name = q.Name, DataValues = q.Data.Aggregate ("", (acc, t) => (acc == "" ? "" :
acc + ",") + t.DataValue) });