Entity Framework Doesn't add to the Database

I'm using entity framework to register a customer using Windows Form but after calling the add method and calling the savechange method the row doesn't insert and i don't know why here is my code: there is a primary key column named Cid which is identity

it is a register form when ever from the main form the user click on the register button this form loads and he enters his data and press the submit button.but when i click the submit button it doesn't add to database after the call to .SaveChanges() I close my forms and see the data from the server explorer (R-click on the tables and show table data) and it is empty.and even I tried putting a breakpoint in the register form and see if the 'db' has any data which is none

here is my code:

public partial class RegisterForm : Form
{
    PachinEntities1 db=new PachinEntities1();
    private Customer temp;
    public RegisterForm()
    {
        InitializeComponent();
    }

    private void button2_Click(object sender, EventArgs e)
    {
        this.Close();  
    }

    private void RegisterForm_Load(object sender, EventArgs e)
    {
        temp=new Customer();
        DateTime gocal = DateTime.Now;
        PersianCalendar pcal=new PersianCalendar();
        int year=pcal.GetYear(gocal);
        int month = pcal.GetMonth(gocal);
        int day = pcal.GetDayOfMonth(gocal);
        string pday = string.Format("{0}/{1}/{2}", year, month, day);
        temp.Date = pday;
        txt_Date.Text = pday;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        if (txt_Name.Text.Trim().Length != 0)
        {

            if (txt_Tell1.Text.Trim().Length != 0)
            {
                if (txt_Address.Text.Trim().Length != 0)
                {
                    temp.Name = txt_Name.Text;
                    temp.Tell1 = txt_Tell1.Text;
                    temp.Tell2 = txt_Tell2.Text;
                    temp.Address = txt_Address.Text;
                    db.Customers.Add(temp);
                    db.SaveChanges();
                }
                else
                {
                    MessageBox.Show("آدرس را وارد کنید");
                }
            }
            else
            {
                MessageBox.Show("شماره تلفن را وارد کنید");
            }
        }
        else
        {
            MessageBox.Show("نام را وارد کنید");
        }
    }
}