实体框架4.1检索自参照数据 [英] Entity Framework 4.1 Retrieving self referencing data

问题描述

我第一次使用实体框架4.1 code和ASP.NET MVC 3，我努力妥善让我自参考设置。我有一个Category类。它必须是自参考到自身。一个类别可以是一个父类别时，在表中的ParentCategoryId为空。如果一个类具有一个值的ParentCategoryId则表示它属于一个父类别

I am using Entity Framework 4.1 code first and ASP.NET MVC 3 and I am struggling to get my self referencing setup properly. I have a Category class. It must be self referencing to itself. A category can be a parent category when the ParentCategoryId in the table is null. If a category has a ParentCategoryId with a value then it means that it belongs to a parent category.

我跟着这个<一个href=\"http://www.$c$cproject.com/Articles/206410/How-to-Configure-a-Self-Referencing-Entity-in-$c$c\">article在code项目。

I followed this article on Code Project.

下面是我的Category类：

Here is my Category class:

public class Category
{
     public int Id { get; set; }
     public string Name { get; set; }
     public string Description { get; set; }
     public string MetaKeywords { get; set; }
     public string MetaDescription { get; set; }
     public bool IsActive { get; set; }
     public virtual Category ParentCategory { get; set; }
     public int? ParentCategoryId { get; set; }
}

我的上下文类：

public class PbeContext : DbContext
{
     public DbSet<Category> Categories { get; set; }

     protected override void OnModelCreating(DbModelBuilder dbModelBuilder)
     {
          dbModelBuilder.Conventions.Remove<PluralizingTableNameConvention>();

          dbModelBuilder.Entity<Category>()
               .HasOptional(c => c.ParentCategory)
               .WithMany()
               .HasForeignKey(p => p.ParentCategoryId);
     }
}

不知道上面是正确的？

Not sure if the above is correct?

有人可以帮我得到这个权利？我需要的是，当我通过ID查询类别，那么它必须带回父类（仅在需要时加载）。此外，它必须加载所有子类（仅在需要时）。我还没有被添加到列表中的类别类子类别。

Can someone please help me get this right? What I need is that when I query a category by id then it must bring back the parent category (only loaded when needed). Also it must load any child categories (only when needed). I have not yet added a list to the category class for the child categories.

你会上面quesries模样检索类别与它的父类别和子类别？

What would the above quesries look like to retrieve a category with it parent category and child categories?

修改

这是我如何找回我的类别：

This is how I retrieve my category:

public Category GetById(int id)
{
     return db
          .Categories
          .Find(id);
}

由于ParentCategory参考可以为空，我将如何在视图中显示此？我有以下几点：

Because the ParentCategory reference can be null, how would I display this in the view? I have the following:

@Model.ParentCategory.Name

..但不给一个错误，如果该类别有没有与之相关的父类？我怎么会在视图中显示呢？

..but won't it give an error if the category has no parent category associated with it? How would I display it in the view?

推荐答案

如果您需要访问子类可以集合属性添加到模型

If you need to access child categories you can add a collection property to your model

public class Category
{
     public int Id { get; set; }
     public string Name { get; set; }
     public string Description { get; set; }
     public string MetaKeywords { get; set; }
     public string MetaDescription { get; set; }
     public bool IsActive { get; set; }
     public virtual Category ParentCategory { get; set; }
     public int? ParentCategoryId { get; set; }
     public virtual ICollection<Category> ChildCategories{ get; set; }
}

然后你可以设置模型

Then you can setup the model as

      dbModelBuilder.Entity<Category>()
           .HasOptional(c => c.ParentCategory)
           .WithMany(c => ChildCategories)
           .HasForeignKey(p => p.ParentCategoryId);

修改

您应该检查 ParentCategory 是否为空或不是。<​​/ P>

You should check whether ParentCategory is null or not.

@if(Model.ParentCategory != null){
  <div>@Model.ParentCategory.Name</div>
}

这篇关于实体框架4.1检索自参照数据的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！