[渣译文] 使用 MVC 5 的 EF6 Code First 入门 系列：为ASP.NET MVC应用程序处理并发

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace ContosoUniversity.Models
{
    public class Department
    {
        public int DepartmentID { get; set; }

        [StringLength(50, MinimumLength = 3)]
        public string Name { get; set; }

        [DataType(DataType.Currency)]
        [Column(TypeName = "money")]
        public decimal Budget { get; set; }

        [DataType(DataType.Date)]
        [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
        [Display(Name = "起始日期")]
        public DateTime StartDate { get; set; }

        [Display(Name = "系主任")]
        public int? InstructorID { get; set; }

        1433837376
        public byte[] RowVersion { get; set; }

        public virtual Instructor Administrator { get; set; }
        public virtual ICollection<Course> Courses { get; set; }
    }
}

modelBuilder.Entity<Department>().Property(p => p.RowVersion).IsConcurrencyToken();

Add-Migration RowVersion 
Update-Database

using System.Data.Entity.Infrastructure;

ViewBag.InstructorID = new SelectList(db.Instructors, "ID", "FullName");

        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<ActionResult> Edit([Bind(Include = "DepartmentID,Name,Budget,StartDate,InstructorID")] Department department)
        {
            try
            {
                if (ModelState.IsValid)
                {
                    db.Entry(department).State = EntityState.Modified;
                    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, "无法保存更改，系已经被其他用户删除。");
                }
                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: "
                            + String.Format("{0:c}", databaseValues.Budget));
                    if (databaseValues.StartDate != clientValues.StartDate)
                        ModelState.AddModelError("StartDate", "当前值: "
                            + String.Format("{0:d}", 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。如果你仍然想要保存这些数据，"
                    + "重新点击保存按钮或者点击返回列表撤销本次操作。");
                    department.RowVersion = databaseValues.RowVersion;
                }
            }
            catch (RetryLimitExceededException)
            {
                ModelState.AddModelError(string.Empty, "无法保存更改，请重试或联系管理员。");
            }
            ViewBag.InstructorID = new SelectList(db.Instructors, "ID", "FullName", department.InstructorID);
            return View(department);
        }

var entry = ex.Entries.Single();

var clientValues = (Department)entry.Entity;
var databaseEntry = entry.GetDatabaseValues();

if (databaseEntry == null)
{
    ModelState.AddModelError(string.Empty, "无法保存更改，系已经被其他用户删除。");
}
else
{
    var databaseValues = (Department)databaseEntry.ToObject();                 

if (databaseValues.Name != clientValues.Name)
      ModelState.AddModelError("Name", "当前值: " + databaseValues.Name);

ModelState.AddModelError(string.Empty, "当前记录已经被其他人更改。如果你仍然想要保存这些数据，"
+ "重新点击保存按钮或者点击返回列表撤销本次操作。");                

@model ContosoUniversity.Models.Department

@{
    ViewBag.Title = "Edit";
}

<h2>Edit</h2>


@using (Html.BeginForm())
{
    @Html.AntiForgeryToken()

    <div class="form-horizontal">
        <h4>Department</h4>
        <hr />
        @Html.ValidationSummary(true)
        @Html.HiddenFor(model => model.DepartmentID)
        @Html.HiddenFor(model => model.RowVersion)

        public async Task<ActionResult> Delete(int? id,bool? concurrencyError)
        {
            if (id == null)
            {
                return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
            }
            Department department = await db.Departments.FindAsync(id);
            if (department == null)
            {
                if (concurrencyError == true)
                {
                    return RedirectToAction("Index");
                }
                return HttpNotFound();
            }
            if (concurrencyError.GetValueOrDefault())
            {
                if (department == null)
                {
                    ViewBag.ConcurrencyErrorMessage = "你想要删除的记录"
                        + "已经被另一个用户删除了，点击列表超链接返回。";
                }
                else
                {
                    ViewBag.ConcurrencyErrorMessage = "你想要删除的记录"
                        + "被另一个用户修改了原始值，如果您仍然想要删除该条记录"
                        + "再次点击删除按钮，或者点击列表超链接返回。";
                }
            }
            return View(department);
        }

        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<ActionResult> Delete(Department department)
        {
            try
            {
                db.Entry(department).State = EntityState.Deleted;
                await db.SaveChangesAsync();
                return RedirectToAction("Index");
            }
            catch (DbUpdateConcurrencyException)
            {
                return RedirectToAction("Delete", new { concurrencyError = true, id = department.DepartmentID });
            }
            catch   (DataException)
            {
                ModelState.AddModelError(string.Empty, "无法删除，请重试或联系管理员。");
                return View(department);
            }
        }

        public async Task<ActionResult> DeleteConfirmed(int id)

        public async Task<ActionResult> Delete(Department department)

@model ContosoUniversity.Models.Department

@{
    ViewBag.Title = "Delete";
}

<h2>Delete</h2>
<p class="error">@ViewBag.ConcurrencyErrorMessage</p>
<h3>Are you sure you want to delete this?</h3>
<div>
    <h4>Department</h4>
    <hr />
    <dl class="dl-horizontal">
        <dt>
            Administrator
        </dt>

        <dd>
            @Html.DisplayFor(model => model.Administrator.FullName)
        </dd>

        <dt>
            @Html.DisplayNameFor(model => model.Name)
        </dt>

        <dd>
            @Html.DisplayFor(model => model.Name)
        </dd>

        <dt>
            @Html.DisplayNameFor(model => model.Budget)
        </dt>

        <dd>
            @Html.DisplayFor(model => model.Budget)
        </dd>

        <dt>
            @Html.DisplayNameFor(model => model.StartDate)
        </dt>

        <dd>
            @Html.DisplayFor(model => model.StartDate)
        </dd>

    </dl>

    @using (Html.BeginForm()) {
        @Html.AntiForgeryToken()
        @Html.HiddenFor(model => model.DepartmentID)
        @Html.HiddenFor(model => model.RowVersion)

        <div class="form-actions no-color">
            <input type="submit" value="Delete" class="btn btn-default" /> |
            @Html.ActionLink("Back to List", "Index")
        </div>
    }
</div>

<p class="error">@ViewBag.ConcurrencyErrorMessage</p>

<dt>
  Administrator
</dt>
<dd>
  @Html.DisplayFor(model => model.Administrator.FullName)
</dd>

@Html.HiddenFor(model => model.DepartmentID)
@Html.HiddenFor(model => model.RowVersion)