我正试图通过 LINQ-SQL . 我正在尝试以下方法

using(DataContext obj = new DataContext())
        {
            mdc_meters_data data = new mdc_meters_data();
            data.cust_id = cust_id;
            data.device_id = Convert.ToString(device_id);
            data.kwh = Convert.ToString(e_val);
            data.voltage_p1 = Convert.ToString(a_vol_val);
            data.voltage_p2 = Convert.ToString(b_vol_val);
            data.voltage_p2 = Convert.ToString(c_vol_val);
            data.current_p1 = Convert.ToString(a_curr_val);
            data.current_p2 = Convert.ToString(b_curr_val);
            data.current_p3 = Convert.ToString(c_curr_val);
            data.data_date_time = Convert.ToDateTime(theDate.ToString(format));
            data.d_type = Convert.ToString(d_type);
            data.pf1 = Convert.ToString(a_pf_val);
            data.pf2 = Convert.ToString(b_pf_val);
            data.pf3 = Convert.ToString(c_pf_val);
            data.p_id = p_id;
            // executes the commands to implement the changes to the database
            obj.SubmitChanges();
        }

我得到的错误是
“datacontext”不包含“submitchanges”的定义，并且找不到接受类型为“datacontext”的第一个参数的可访问扩展方法“submitchanges”
更新1
我做错了，所以我试着用继承的类来做 DbContext 班级。但不知什么原因，它仍然没有插入数据

using(mdc_dbEntities obj = new mdc_dbEntities())
        {
            mdc_meters_data data = new mdc_meters_data();
            data.cust_id = cust_id;
            data.device_id = Convert.ToString(device_id);
            data.kwh = Convert.ToString(e_val);
            data.voltage_p1 = Convert.ToString(a_vol_val);
            data.voltage_p2 = Convert.ToString(b_vol_val);
            data.voltage_p2 = Convert.ToString(c_vol_val);
            data.current_p1 = Convert.ToString(a_curr_val);
            data.current_p2 = Convert.ToString(b_curr_val);
            data.current_p3 = Convert.ToString(c_curr_val);
            data.data_date_time = Convert.ToDateTime(theDate.ToString(format));
            data.d_type = Convert.ToString(d_type);
            data.pf1 = Convert.ToString(a_pf_val);
            data.pf2 = Convert.ToString(b_pf_val);
            data.pf3 = Convert.ToString(c_pf_val);
            data.p_id = p_id;
            // executes the commands to implement the changes to the database
            obj.SaveChanges();
        }