乐观同步

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<ActionResult> Edit(int? id, byte[] rowVersion)
{
    string[] fieldsToBind = new string[] { "Name", "Budget", "StartDate", "InstructorID", "RowVersion" };
    if (id == null)
    {
        return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
    }
    var departmentToUpdate = await db.Departments.FindAsync(id);
    if (departmentToUpdate == null)
    {
        Department deletedDepartment = new Department();
        TryUpdateModel(deletedDepartment, fieldsToBind);
        ModelState.AddModelError(string.Empty, "Unable to save changes, the department was deleted by another user");
        ViewBag.InstructorID = new SelectList(db.Instructors, "ID", "FullName", deletedDepartment.InstructorID);
        return View(deletedDepartment);
    }
    if (TryUpdateModel(departmentToUpdate, fieldsToBind))
    {
        try
        {
            db.Entry(departmentToUpdate).OriginalValues["RowVersion"] = rowVersion;
            await db.SaveChangesAsync();
            return RedirectToAction("Index");
        }
        catch (DbUpdateConcurrencyException ex)
        {
            var entry = ex.Entries.Single();
            var clientValues = (Department)entry.Entity;
            var databaseEntry = entry.GetDatabaseValues();
            if (databaseEntry == null)
            {
                ModelState.AddModelError(string.Empty, "无法保持更改，系已被其他用户删除");
            }
            else
            {
                var databaseValues = (Department)databaseEntry.ToObject();
                if (databaseValues.Name != clientValues.Name)
                {
                    ModelState.AddModelError("Name", "当前值：" + databaseValues.Name);
                }
                if (databaseValues.Budget != clientValues.Budget)
                {
                    ModelState.AddModelError("Budget", "当前值：" + databaseValues.Budget);
                }
                if (databaseValues.StartDate != clientValues.StartDate)
                {
                    ModelState.AddModelError("StartDate", "当前值：" + databaseValues.StartDate);
                }
                if (databaseValues.InstructorID != clientValues.InstructorID)
                {
                    ModelState.AddModelError("InstructorID", "当前值：" + db.Instructors.Find(databaseValues.InstructorID).FullName);
                }
                ModelState.AddModelError(string.Empty, "当前记录已经被其他人更改，如果你仍要保存这些数据，重新点击保持按钮或点击返回列表撤销本次操作");
                departmentToUpdate.RowVersion = databaseValues.RowVersion;
            }
        }
        catch (RetryLimitExceededException)
        {
            ModelState.AddModelError(string.Empty, "无法保持更改");
        }
    }
    ViewBag.InstructorID = new SelectList(db.Instructors, "ID", "FullName", departmentToUpdate.InstructorID);
    return View(departmentToUpdate);
}