C# 多对多关系基本示例(MVC3)
我有一个MVC3 C项目,我有一个FoodItem和FoodItemCategory的模型。这两个模型如下所示:C# 多对多关系基本示例(MVC3),c#,asp.net-mvc-3,entity-framework-4,scaffolding,sql-server-ce-4,C#,Asp.net Mvc 3,Entity Framework 4,Scaffolding,Sql Server Ce 4,我有一个MVC3 C项目,我有一个FoodItem和FoodItemCategory的模型。这两个模型如下所示: public class FoodItem { public int ID { get; set; } [Required] public string Name { get; set; } public string Description { get; set; } public virtual ICollection<FoodIte
public class FoodItem
{
public int ID { get; set; }
[Required]
public string Name { get; set; }
public string Description { get; set; }
public virtual ICollection<FoodItemCategory> Categories { get; set; }
public DateTime CreateDate { get; set; }
}
public class FoodItemCategory {
public int ID { get; set; }
public string Name { get; set; }
public string Description { get; set; }
public virtual ICollection<FoodItem> FoodItems { get; set; }
public DateTime CreateDate { get; set; }
}
公共类FoodItem
{
公共int ID{get;set;}
[必需]
公共字符串名称{get;set;}
公共字符串说明{get;set;}
公共虚拟ICollection类别{get;set;}
公共日期时间CreateDate{get;set;}
}
公共类食品分类{
公共int ID{get;set;}
公共字符串名称{get;set;}
公共字符串说明{get;set;}
公共虚拟ICollection FoodItems{get;set;}
公共日期时间CreateDate{get;set;}
}
我有一个_CreateOrEdit.cshtml视图,它最初是从架子工生成的,我对它进行了修改,以包含所有类别,并选中食品所属的框。一种食物可以有许多或所有的类别。该视图如下所示:
@model StackOverFlowIssue.Models.FoodItem
<div class="editor-label">
@Html.LabelFor(model => model.Name)
</div>
<div class="editor-field">
@Html.EditorFor(model => model.Name)
@Html.ValidationMessageFor(model => model.Name)
</div>
<div class="editor-label">
@Html.LabelFor(model => model.Description)
</div>
<div class="editor-field">
@Html.EditorFor(model => model.Description)
@Html.ValidationMessageFor(model => model.Description)
</div>
<div class="editor-label">
@Html.LabelFor(model => model.Categories)
</div>
<div class="editor-field">
@foreach (var FoodItemCategory in (IEnumerable<StackOverFlowIssue.Models.FoodItemCategory>)ViewBag.Categories){
<input type="checkbox" name="FoodItemCategoryId" value="@FoodItemCategory.ID"
@foreach(var c in Model.Categories){
if(c.ID == FoodItemCategory.ID){
@String.Format("checked=\"checked\"")
}
}
/>
@FoodItemCategory.Name
<br />
}
</div>
@Html.Hidden("CreateDate", @DateTime.Now)
[HttpPost]
public ActionResult Edit(FoodItem foodItem)
{
if (ModelState.IsValid)
{
var cList = Request["CategoryId"].Split(',');
List<FoodItemCategory> categories = new List<FoodItemCategory>();
foreach (var c in cList) {
var ci = Convert.ToInt32(c);
FoodItemCategory category = context.FoodItemCategories.Single(x => x.ID == ci);
categories.Add(category);
}
context.Entry(foodItem).State = EntityState.Modified;
restaurant.Categories = categories;
context.SaveChanges();
return RedirectToAction("Index");
}
return View(foodItem);
}
@model StackOverFlowIssue.Models.FoodItem
@LabelFor(model=>model.Name)
@EditorFor(model=>model.Name)
@Html.ValidationMessageFor(model=>model.Name)
@LabelFor(model=>model.Description)
@EditorFor(model=>model.Description)
@Html.ValidationMessageFor(model=>model.Description)
@LabelFor(model=>model.Categories)
@foreach(在(IEnumerable)ViewBag.Categories中的变量FoodItemCategory){
@FoodItemCategory.Name
}
@Html.Hidden(“CreateDate”,@DateTime.Now)
如您所见,我有一个嵌套循环,为每个类别创建一个复选框,在创建每个类别时,我在模型的Categories属性中循环并检查该特定类别。如果它存在,我设置复选框的checked属性。如果选中一个框并单击保存,则在控制器上的HttpPost操作上,我将执行以下操作:
@model StackOverFlowIssue.Models.FoodItem
<div class="editor-label">
@Html.LabelFor(model => model.Name)
</div>
<div class="editor-field">
@Html.EditorFor(model => model.Name)
@Html.ValidationMessageFor(model => model.Name)
</div>
<div class="editor-label">
@Html.LabelFor(model => model.Description)
</div>
<div class="editor-field">
@Html.EditorFor(model => model.Description)
@Html.ValidationMessageFor(model => model.Description)
</div>
<div class="editor-label">
@Html.LabelFor(model => model.Categories)
</div>
<div class="editor-field">
@foreach (var FoodItemCategory in (IEnumerable<StackOverFlowIssue.Models.FoodItemCategory>)ViewBag.Categories){
<input type="checkbox" name="FoodItemCategoryId" value="@FoodItemCategory.ID"
@foreach(var c in Model.Categories){
if(c.ID == FoodItemCategory.ID){
@String.Format("checked=\"checked\"")
}
}
/>
@FoodItemCategory.Name
<br />
}
</div>
@Html.Hidden("CreateDate", @DateTime.Now)
[HttpPost]
public ActionResult Edit(FoodItem foodItem)
{
if (ModelState.IsValid)
{
var cList = Request["CategoryId"].Split(',');
List<FoodItemCategory> categories = new List<FoodItemCategory>();
foreach (var c in cList) {
var ci = Convert.ToInt32(c);
FoodItemCategory category = context.FoodItemCategories.Single(x => x.ID == ci);
categories.Add(category);
}
context.Entry(foodItem).State = EntityState.Modified;
restaurant.Categories = categories;
context.SaveChanges();
return RedirectToAction("Index");
}
return View(foodItem);
}
[HttpPost]
公共行动结果编辑(FoodItem FoodItem)
{
if(ModelState.IsValid)
{
var cList=Request[“CategoryId”].Split(',');
列表类别=新列表();
foreach(cList中的var c){
var ci=转换为32(c);
FoodItemCategory category=context.FoodItemCategories.Single(x=>x.ID==ci);
类别。添加(类别);
}
context.Entry(foodItem).State=EntityState.Modified;
餐厅。类别=类别;
SaveChanges();
返回操作(“索引”);
}
返回视图(foodItem);
}
我可以保存一次类别。如果我返回视图,只需单击“保存”,我将收到以下错误:
无法将重复值插入到唯一索引中。[表名=>FoodItemCategoryFoodItems,约束名称=PK\u FoodItemCategoryFoodItems\u00000000000000 A8]
描述:执行当前web请求期间发生未处理的异常。请>查看堆栈跟踪以了解有关错误的更多信息以及错误在代码中的起源
异常详细信息:System.Data.SqlServerCe.SqlCeException:无法将重复值插入到>唯一索引中。[表名=FoodItemCategoryFoodItems,约束名称=>PK\u FoodItemCategoryFoodItems\u00000000000000 a8]
源错误:
第97行:context.Entry(foodItem).State=EntityState.Modified;
第98行:foodItem.Categories=类别;
第99行:context.SaveChanges();
第100行:返回重定向操作(“索引”);
第101行:}
不确定这是否重要,但我使用的是SQLServer Compact Edition 4。我这样做对吗?对于这样的东西,通常的编码实践是什么?我知道同样的情况每天都会发生,因为同样的关系模型在很多情况下都会用到,比如博客等。尝试类似的方法(未经测试):
这看起来效率很低,但因为您处理的是多对多关系,可以在视图中添加或删除关系,所以这是唯一的方法。原因是:
- 您必须说明添加了哪些关系,删除了哪些关系
- 如果只添加所有相关类别,则再次插入关系
- 您不能说删除了哪些关系,因为您不传输有关未选中类别的信息
- 您必须说明添加了哪些关系,删除了哪些关系
- 如果只添加所有相关类别,则再次插入关系
- 您不能说删除了哪些关系,因为您不传输有关未选中类别的信息
有关分离对象图和处理关系的更多信息,请参阅。这是关于ObjectContext API的,但DbContext API只是一个包装器,因此同样的限制仍然存在。除了Ladislav的答案之外,您还可以使用以下方法来摆脱请求[].split()部分:
[HttpPost]
public ActionResult Edit(FoodItem foodItem, ICollection<int> CategoryId)
{
if (ModelState.IsValid)
{
int id = foodItem.Id;
// Load food item with related categories first
var item = context.FoodItems
.Include(f => f.Categories)
.Single(f => f.Id == id);
// Process changed scalar values
context.Entry(item).CurrentValues.SetValues(foodItem);
// Brute force processing of relations
// This can be optimized - instead of deleting all and adding all again
// you can manually compare which relations already exists, add new and
// remove non existing but let's make that as a homework
item.Categories.Clear();
foreach (var id in CategoryID)
{
// Use find - if category was already loaded in the first query, it will
// be reused without additional query to DB
var category = context.Categories.Find(id);
// Now add category to attached food item to create new relation
item.Categories.Add(category);
}
context.SaveChanges();
return RedirectToAction("Index");
}
return View(foodItem);
}
[HttpPost]
公共操作结果编辑(FoodItem FoodItem,ICollection类别ID)
{
if(ModelState.IsValid)
{
int id=foodItem.id;
//首先加载具有相关类别的食品
var item=context.FoodItems
.包括(f=>f.类别)
.Single(f=>f.Id==Id);
//处理更改的标量值
context.Entry(item).CurrentValues.SetValues(foodItem);
//计算机的蛮力处理