void categoryList()
{
studentlearnEntities1 dbs = new studentlearnEntities1();
var categories = dbs.categories.ToList();
categoryTypeCombo.DataSource = categories;
categoryTypeCombo.DisplayMember = "name";
categoryTypeCombo.ValueMember = "id";
}
void studentList()
{
studentlearnEntities1 db = new studentlearnEntities1();
List <user> students = (from item in db.users
where item.authority == 1
select item).ToList();
studentCombobox.DataSource = students;
studentCombobox.DisplayMember = "name";
studentCombobox.ValueMember = "id";
}
