public void AddSage(Sage item)
{
var context = new SBContext();
context.Sages.Add(item);
context.SaveChanges();
}
private void add_Click(object sender, EventArgs e)
{
String str = listBox1.SelectedItem.ToString();
Books book = db.Book.Where(b => b.Name == str).FirstOrDefault();
Sage sage = db.Sages.Find(id);
sage.Book.Add(book);
db.Entry(sage).State = System.Data.Entity.EntityState.Modified;
db.SaveChanges();
UpdateListBoxes();
}