protected void Page_PreRender(object sender, EventArgs e) { if (ddlClass.SelectedItem == null || ddlMedium.SelectedItem == null) { ddlClass.DataBind(); ddlMedium.DataBind(); CheckBoxListSubjects.DataBind(); } var subjectTables = PageDataService.GetAllSubjectTableRecordsForClassAndMediumAdoNet(Convert.ToInt32(ddlClass.SelectedItem.Value), Convert.ToInt32(ddlMedium.SelectedItem.Value)); foreach (ListItem listItem in CheckBoxListSubjects.Items) { listItem.Selected = false; } var listItems = (from ListItem listItem in CheckBoxListSubjects.Items join subjectTable in subjectTables on listItem.Value equals Convert.ToString(subjectTable.SubjectId) select listItem); foreach (var listItem in listItems) { listItem.Selected = true; } }