如何在ASP.NET实体框架中不允许重复

Question

我是ASP.NET MVC和EF的新手，所以这可能是一个非常简单的问题，但防止用户尝试输入重复记录的最佳方法是什么？

我有一个名为Category的表，它有两列Id和CategoryName(Id是PK，我在CategoryName上将索引值设置为唯一(。我想做的是防止用户输入相同的类别。

我的CategoriesController看起来像：

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Entity;
using System.Linq;
using System.Net;
using System.Web;
using System.Web.Mvc;
using Library;
namespace Library.Controllers
{
public class CategoriesController : Controller
{
private LibraryDbEntities1 db = new LibraryDbEntities1();
// GET: Categories
public ActionResult Index()
{
return View(db.Category.ToList());
}
// GET: Categories/Details/5
public ActionResult Details(int? id)
{
if (id == null)
{
return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
}
Category category = db.Category.Find(id);
if (category == null)
{
return HttpNotFound();
}
return View(category);
}
// GET: Categories/Create
public ActionResult Create()
{
return View();
}
// POST: Categories/Create
// To protect from overposting attacks, enable the specific properties you want to bind to, for 
// more details see https://go.microsoft.com/fwlink/?LinkId=317598.
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create([Bind(Include = "Id,CategoryName")] Category category)
{
if (ModelState.IsValid)
{
db.Category.Add(category);
db.SaveChanges();
return RedirectToAction("Index");
}
int temp = Convert.ToInt32(cmd.ExcecuteScalar().To)
return View(category);
}
// GET: Categories/Edit/5
public ActionResult Edit(int? id)
{
if (id == null)
{
return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
}
Category category = db.Category.Find(id);
if (category == null)
{
return HttpNotFound();
}
return View(category);
}
// POST: Categories/Edit/5
// To protect from overposting attacks, enable the specific properties you want to bind to, for 
// more details see https://go.microsoft.com/fwlink/?LinkId=317598.
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit([Bind(Include = "Id,CategoryName")] Category category)
{
if (ModelState.IsValid)
{
db.Entry(category).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
return View(category);
}
// GET: Categories/Delete/5
public ActionResult Delete(int? id)
{
if (id == null)
{
return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
}
Category category = db.Category.Find(id);
if (category == null)
{
return HttpNotFound();
}
return View(category);
}
// POST: Categories/Delete/5
[HttpPost, ActionName("Delete")]
[ValidateAntiForgeryToken]
public ActionResult DeleteConfirmed(int id)
{
Category category = db.Category.Find(id);
db.Category.Remove(category);
db.SaveChanges();
return RedirectToAction("Index");
}
protected override void Dispose(bool disposing)
{
if (disposing)
{
db.Dispose();
}
base.Dispose(disposing);
}
}
}

索引视图如下所示：

@model Library.Category
@{
ViewBag.Title = "Create";
}
<h2>Create</h2>
@using (Html.BeginForm()) 
{
@Html.AntiForgeryToken()

<div class="form-horizontal">
<h4>Category</h4>
<hr />
@Html.ValidationSummary(true, "", new { @class = "text-danger" })
<div class="form-group">
@Html.LabelFor(model => model.Id, htmlAttributes: new { @class = "control-label col-md-2" })
<div class="col-md-10">
@Html.EditorFor(model => model.Id, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.Id, "", new { @class = "text-danger" })
</div>
</div>
<div class="form-group">
@Html.LabelFor(model => model.CategoryName, htmlAttributes: new { @class = "control-label col-md-2" })
<div class="col-md-10">
@Html.EditorFor(model => model.CategoryName, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.CategoryName, "", new { @class = "text-danger" })
</div>
</div>
<div class="form-group">
<div class="col-md-offset-2 col-md-10">
<input type="submit" value="Create" class="btn btn-default" />
</div>
</div>
</div>
}
<div>
@Html.ActionLink("Back to List", "Index")
</div>
@section Scripts {
@Scripts.Render("~/bundles/jqueryval")
}

我的问题是：如何防止用户两次进入同一类别？例如，我创建了一个名为"；动作"；，我不希望任何其他用户能够创建相同的类别。

Answer 1

正如我在上面的评论中所说，您有两个选项。一种是向CategoryName字段添加一个唯一索引。这将强制数据库拒绝无效的更新。当然，这意味着您的代码中有一个异常需要处理。

我更喜欢在代码中处理这种情况，尽可能避免出现异常
对于"创建"操作，这包括检查数据库是否存在与建议的类别名称相同的类别名称。

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create([Bind(Include = "Id,CategoryName")] Category category)
{
ViewBag.ErrorMessage = "";
if (ModelState.IsValid)
{
// Check if the cat name exists or not
var cat = db.Category.FirstOrDefault(x => x.CategoryName == category.CategoryName);
if(cat == null)
{
db.Category.Add(category);
db.SaveChanges();
return RedirectToAction("Index");
}
else
{
// Add here the logic required to inform your user about the problem
ViewBag.ErrorMessage = "Duplicate Category Name";

}
}
return View(category);
}

但是您在"编辑"操作中也有同样的问题。在这里，您也应该防止您的用户将现有的CategoryName更改为另一个现有的CategoryName，但如果数据库中存在的类别与您的用户正在编辑的类别相同，则不要更改。

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit([Bind(Include = "Id,CategoryName")] Category category)
{
ViewBag.ErrorMessage = "";
if (ModelState.IsValid)
{
var cat = db.Category.FirstOrDefault(x => x.CategoryName == category.CategoryName  
&& x.Id != category.Id)
if(cat == null)
{
db.Entry(category).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
else
{
// Inform your user about the problem
ViewBag.ErrorMessage = "Duplicate category Name";
}
}
return View(category);
}

最后，您可以在.cshtml中通知用户添加一个特定的DIV，并将错误消息存储在ViewBag中。当然，您可以添加一些style/css类(红色背景/颜色(来吸引用户对消息的注意。

@using (Html.BeginForm()) 
{
if (!string.IsNullOrEmpty(ViewBag.ErrorMessage))
{
<div>
<p>
<h3>@Html.Raw(ViewBag.ErrorMessage)</h3>
</p>
</div>
}
@Html.AntiForgeryToken()

<div class="form-horizontal">