How do I save datagridview edits back into the database through entity framework?

I've bound my combobox so that the value selected will appear on the datagridview. However, although the datagridview is editable, the changes made won't save back to the database even is I use db.SaveChanges(). Is there another method?

private void cboeCID_SelectedIndexChanged_1(object sender, EventArgs e)
        {
            var CID = Convert.ToInt32(cboeCID.Text);

            using (var db = new Entities2())
            {

                var course = from c in db.Student_Course
                             where c.CID == CID
                             select new Class1
                             {
                                 SID = c.SID,
                                 Mark = c.Mark

                             };

                editDataGridView.DataSource = course.ToList();
            }