سلام و خسته نباشید من یک دیتا گرید دارم که میخوام اطلاعات هر سطر دونه دونه به دیتابیس اد بشه

کدی که نوشتم اینه ولی ارور 

Cannot add an entity that already exists

میده

 tblDaftarForosh tForosh = <span class="hljs-keyword">new</span> tblDaftarForosh();
                PersianCalendar pc = <span class="hljs-keyword">new</span> PersianCalendar();
                <span class="hljs-keyword">string</span> Datee = pc.GetYear(DateTime.Now).ToString() + <span class="hljs-string">"/"</span> + pc.GetMonth(DateTime.Now).ToString(<span class="hljs-string">"0#"</span>) + <span class="hljs-string">"/"</span> + pc.GetDayOfMonth(DateTime.Now).ToString(<span class="hljs-string">"0#"</span>);
                <span class="hljs-keyword">for</span> (<span class="hljs-keyword">int</span> i = <span class="hljs-number">0</span>; i < dgvForosh.Rows.Count; i++)
                {
                   
                    tForosh.NameKala = dgvForosh.Rows[i].Cells[<span class="hljs-number">0</span>].Value.ToString();
                    tForosh.GhV = Convert.ToInt32(dgvForosh.Rows[i].Cells[<span class="hljs-number">1</span>].Value);
                    tForosh.Tedad = Convert.ToInt32(dgvForosh.Rows[i].Cells[<span class="hljs-number">2</span>].Value);
                    tForosh.GhKolkala = Convert.ToInt32(dgvForosh.Rows[i].Cells[<span class="hljs-number">3</span>].Value);
                    tForosh.GhKh = Convert.ToInt32(dgvForosh.Rows[i].Cells[<span class="hljs-number">4</span>].Value);
                    tForosh.Takhfif = Convert.ToInt32(txtTakhfif.Text);
                    tForosh.TDarsad = Convert.ToInt32(txtTDarsad.Text);
                    tForosh.TJashn = Convert.ToInt32(txtTJashnvare.Text);
                    tForosh.Date = Datee;
                    tForosh.Time = DateTime.Now.ToShortTimeString();
                    db.tblDaftarForoshes.InsertOnSubmit(tForosh);
                    db.SubmitChanges();
                }