DbContext.SaveChanges（）不会将更改保存到数据库

Question

DbContext.SaveChanges（）不会将更改保存到数据库，但会更新网格。我想要的方法不是bSave_Click方法。如何强制它更新数据库？

Windows窗体应用程序的代码如下：

namespace WinFormsApp
{

    public partial class MainForm : Form
    {

        private List<User> users;
        private List<UserType> userTypes;
        private List<DataGridViewUserDTO> usersForGrid;

        public MainForm()
        {
            InitializeComponent();

            GetData();
            PrepareGrid();            
            FillGrid();
        }


        public void GetData()
        {
            using (var dbContext = new DataInFileEntities())
            {
                userTypes = dbContext.UserTypes.ToList();
                users = dbContext.Users.ToList();

                usersForGrid = users.Select(x => new DataGridViewUserDTO() { Id = x.Id, FirstName = x.FirstName, LastName = x.LastName, UserTypeId = x.UserTypeId, CreatedById = x.CreatedById, Created = x.Created, EditedById = x.EditedById, Edited = x.Edited }).ToList();
            }
        }


        public void FillGrid()
        {
            var gridBindingList = new BindingList<DataGridViewUserDTO>(usersForGrid);
            gridBindingSource = new BindingSource(gridBindingList, null);
            dgvUsers.DataSource = gridBindingSource;
        }


        public void PrepareGrid()
        {
            dgvUsers.AutoGenerateColumns = false;

            DataGridViewTextBoxColumn col = new DataGridViewTextBoxColumn();
            col.DataPropertyName = "Id";
            col.HeaderText = "Id";
            col.Name = "Id";
            col.ReadOnly = true;
            col.AutoSizeMode = DataGridViewAutoSizeColumnMode.DisplayedCells;
            dgvUsers.Columns.Add(col);

            col = new DataGridViewTextBoxColumn();
            col.DataPropertyName = "FirstName";
            col.HeaderText = "First Name";
            col.Name = "FirstName";
            dgvUsers.Columns.Add(col);

            col = new DataGridViewTextBoxColumn();
            col.DataPropertyName = "LastName";
            col.HeaderText = "Last Name";
            col.Name = "LastName";
            dgvUsers.Columns.Add(col);

            DataGridViewComboBoxColumn userTypeCol = new DataGridViewComboBoxColumn();
            userTypeCol.DataPropertyName = "UserTypeId";
            userTypeCol.HeaderText = "User Type";
            userTypeCol.Name = "UserTypeId";

            userTypeCol.DataSource = new BindingList<UserType>(userTypes);
            userTypeCol.DisplayMember = "Name";
            userTypeCol.ValueMember = "Id";
            dgvUsers.Columns.Add(userTypeCol);

            col = new DataGridViewTextBoxColumn();
            col.DataPropertyName = "Edited";
            col.HeaderText = "Edited";
            col.Name = "Edited";
            col.ReadOnly = true;
            dgvUsers.Columns.Add(col);

            DataGridViewComboBoxColumn editedByCol = new DataGridViewComboBoxColumn();
            editedByCol.DataPropertyName = "EditedById";
            editedByCol.HeaderText = "Edited By";
            editedByCol.Name = "EditedById";

            editedByCol.DataSource = new BindingList<DataGridViewUserDTO>(usersForGrid);
            editedByCol.DisplayMember = "Name";
            editedByCol.ValueMember = "Id";
            editedByCol.ReadOnly = true;
            dgvUsers.Columns.Add(editedByCol);


            col = new DataGridViewTextBoxColumn();
            col.DataPropertyName = "Created";
            col.HeaderText = "Created";
            col.Name = "Created";
            col.ReadOnly = true;
            dgvUsers.Columns.Add(col);

            DataGridViewComboBoxColumn createdByCol = new DataGridViewComboBoxColumn();
            createdByCol.DataPropertyName = "CreatedById";
            createdByCol.HeaderText = "Created By";
            createdByCol.Name = "CreatedById";

            createdByCol.DataSource = new BindingList<DataGridViewUserDTO>(usersForGrid);
            createdByCol.DisplayMember = "Name";
            createdByCol.ValueMember = "Id";
            createdByCol.ReadOnly = true;
            dgvUsers.Columns.Add(createdByCol);

        }


        private void bSave_Click(object sender, EventArgs e)
        {
            using (var dbContext = new DataInFileEntities())
            {
                foreach (var row in usersForGrid)
                {

                    var dbItem = dbContext.Users.Where(x => x.Id == row.Id).SingleOrDefault();
                    if (dbItem != null)
                    {
                        if (dbItem.FirstName != row.FirstName || dbItem.LastName != row.LastName || dbItem.UserTypeId != row.UserTypeId)
                        {
                            dbItem.FirstName = row.FirstName;
                            dbItem.LastName = row.LastName;
                            dbItem.UserTypeId = row.UserTypeId;
                            dbItem.Edited = DateTime.UtcNow;
                            dbItem.EditedById = 1;                           
                        }
                    }                    
                }

                dbContext.SaveChanges();
            }

            GetData();
            FillGrid();
        }


    }


    public class DataGridViewUserDTO
    {

        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Name { get { return FirstName + " " + LastName; }}
        public byte UserTypeId { get; set; }
        public Nullable<System.DateTimeOffset> Edited { get; set; }
        public Nullable<int> EditedById { get; set; }
        public System.DateTimeOffset Created { get; set; }
        public int CreatedById { get; set; }
    }


}