การเข้าถึง/แก้ไข BindingSource ก่อนทำการ SaveChangesAsync

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TrainingManagement.Dao
{
    class BaseEntity
    {
        public DateTime? CreatedDate { get; set; }
        public string UserCreated { get; set; }
        public DateTime? UpdatedDate { get; set; }
        public string UserModified { get; set; }
    }
    //public class Student : BaseEntity
    //{
    //    public int Id { get; set; }
    //    public string Name { get; set; }
    //}
    public class SchoolContext : TrainingManagement.Model.TrainingManagementEntities
    {
        //public DbSet <Student> Students { get; set; }

        public override int SaveChanges()
        {
            AddTimestamps();
            return base.SaveChanges();
        }

        public override async Task<int> SaveChangesAsync()
        {
            AddTimestamps();
            return await base.SaveChangesAsync();
        }

        private void AddTimestamps()
        {
            var entities = ChangeTracker.Entries().Where(x => x.Entity is BaseEntity && (x.State == EntityState.Added || x.State == EntityState.Modified));
            var currentUsername = "592560";
            //var currentUsername = !string.IsNullOrEmpty(System.Web.HttpContext.Current?.User?.Identity?.Name)
            //    ? HttpContext.Current.User.Identity.Name : "Anonymous";
            foreach (var entity in entities)
            {
                if (entity.State == EntityState.Added)
                {
                    ((BaseEntity)entity.Entity).CreatedDate = DateTime.UtcNow;
                    ((BaseEntity)entity.Entity).UserCreated = currentUsername;
                }
                ((BaseEntity)entity.Entity).UpdatedDate = DateTime.UtcNow;
                ((BaseEntity)entity.Entity).UserModified = currentUsername;
            }
        }
    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using DevExpress;
using MetroFramework;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;

namespace TrainingManagement.Forms
{
    public partial class frmEmployeeMst : Form
    {
        TrainingManagement.Dao.BindingCombobox bindingCombobox = new Dao.BindingCombobox();
        TrainingManagement.Model.TrainingManagementEntities model = new TrainingManagement.Model.TrainingManagementEntities();
        TrainingManagement.Gui.Gui_Datagrid gui_Datagrid = new Gui.Gui_Datagrid();

        public frmEmployeeMst()
        {
            InitializeComponent();
        }

        #region Event CRUD.
        private void Ctrl_ctrlBtnAddClick(object sender, EventArgs e)
        {
            try
            {

                tbEmpId.Focus();
                Model.HR_EMP_MST c = new Model.HR_EMP_MST();
                model.HR_EMP_MST.Add(c);
                hREMPMSTBindingSource.Add(c);
                hREMPMSTBindingSource.MoveLast();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
                hREMPMSTBindingSource.ResetBindings(false);
            }
        }//Add|New
        private async void Ctrl_ctrlBtnSaveClick(object sender, EventArgs e)
        {
            try
            {
                //
                //ต้องการ Assign ค่าให้กับบาง Field ใน Table : HR_EMP_MST
                //เช่น UpdatedBy, UpdatedDate, CreatedBy, CreatedDate ก่อนทำการ save จะทำได้อย่างไรบ้างครับ


                //Original
                hREMPMSTBindingSource.EndEdit();
                await model.SaveChangesAsync();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
                hREMPMSTBindingSource.ResetBindings(false);
            }
        }//Save|Update
        private void Ctrl_ctrlBtnRefreshClick(object sender, EventArgs e)
        {
            hREMPMSTBindingSource.ResetBindings(false);
            foreach (DbEntityEntry entry in model.ChangeTracker.Entries())
            {
                switch (entry.State)
                {
                    case EntityState.Added:
                        entry.State = EntityState.Detached;
                        break;
                    case EntityState.Modified:
                        entry.State = EntityState.Unchanged;

                        break;
                    case EntityState.Deleted:
                        entry.Reload();
                        break;
                }
            }
        }//Read|Refresh
        private void Ctrl_ctrlBtnDeleteClick(object sender, EventArgs e)
        {
            if (MessageBox.Show("Are you sure want to delete this record ?", "Message", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
            {
                model.HR_EMP_MST.Remove(hREMPMSTBindingSource.Current as Model.HR_EMP_MST);
                hREMPMSTBindingSource.RemoveCurrent();
            }
        }//Delete

        private void Ctrl_ctrlBtnSearchClick(object sender, EventArgs e)
        {

        }//Search

        #endregion
        #region Event Misc.
        private void FrmEmployeeMst_Load(object sender, EventArgs e)
        {
            FnBinding();
            FnStart();
            //MetroFramework.MetroMessageBox.Show(this, "Your username and password don't match.", "Message", MessageBoxButtons.YesNoCancel, MessageBoxIcon.Information);
        }
    
private void FnStart()
        {
            model = new Model.TrainingManagementEntities();
            hREMPMSTBindingSource.DataSource = model.HR_EMP_MST.ToList();
            
            dgvMaster1.DataSource = hREMPMSTBindingSource;
            gui_Datagrid.dgvStyte(dgvMaster1);
        }
        private void FnBinding()
        {
            bindingCombobox.FnBindingPostitionCode(cbPositionCode);
            bindingCombobox.FnBindingDeptCode(cbDeptCode);
            bindingCombobox.FnBindingDivCode(cbDivCode);
            bindingCombobox.FnBindingDistrict_id(cbTh_Districts);
            bindingCombobox.FnBindingAmphure_id(cbTh_Amphures);
            bindingCombobox.FnBindingProvince_id(cbTh_Provinces);
            bindingCombobox.FnBindingZipcode_id(cbTh_Zipcodes);

            bindingCombobox.FnBindingUdf(cbNameprefix, "HR_EMP_MST", "HR_NAMEPREFIX", "TH");
            bindingCombobox.FnBindingUdf(cbNameprefix_en, "HR_EMP_MST", "HR_NAMEPREFIXENG", "EN");
            bindingCombobox.FnBindingUdf(cbWorkState, "HR_EMP_MST", "HR_WORKSTATE", "EN");
            bindingCombobox.FnBindingUdf(cbFsState, "HR_EMP_MST", "HR_FSSTATE", "EN");
            bindingCombobox.FnBindingUdf(cbSex, "HR_EMP_MST", "HR_SEX", "TH");
            bindingCombobox.FnBindingUdf(cbLabor, "HR_EMP_MST", "HR_LABOR", "EN");
            bindingCombobox.FnBindingUdf(cbRoute_van, "HR_EMP_MST", "HR_ROUTE_VAN", "TH");
        }

        private static void DisplayTrackedEntities(TrainingManagement.Model.TrainingManagementEntities context)
        {
            Console.WriteLine("Context is tracking {0} entities.", context.ChangeTracker.Entries().Count());
            DbChangeTracker changeTracker = context.ChangeTracker;
            var entries = changeTracker.Entries();
            foreach (var entry in entries)
            {
              
                Console.WriteLine("Entity Name: {0}", entry.Entity.GetType().FullName);
                Console.WriteLine("Status: {0}", entry.State);
            }
        }

        #endregion

    }
}