实体框架4.1检索自引用数据

问题描述

我正在使用Entity Framework 4.1代码，ASP.NET MVC 3，我正在努力使我的自我引用设置正确。我有一个类别类。它必须自我引用。当表中的ParentCategoryId为空时，类别可以是父类别。如果一个类别有一个值为ParentCategoryId，那么这意味着它属于父类。

我遵循这个 on Code Project。

这是我的类别类：

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

我的上下文类：

  public class PbeContext：DbContext 
 {
 public DbSet< Category>分类{get;组; 
 
 protected override void OnModelCreating（DbModelBuilder dbModelBuilder）
 {
 dbModelBuilder.Conventions.Remove< PluralizingTableNameConvention>（）; 
 
 dbModelBuilder.Entity< Category>（）
 .HasOptional（c => c.ParentCategory）
 .WithMany（）
 .HasForeignKey（p => p.ParentCategoryId）; 
} 
} 
  

不知道上述是否正确？ >

有人可以帮我取得这个权利吗？我需要的是，当我通过id查询类别时，它必须带回父类（仅在需要时加载）。还必须加载任何子类别（仅在需要时）。我还没有在子类别的类别类别中添加列表。

上面的quesries将如何检索父类和子类的类别？

编辑

这是我如何检索我的类别：

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

由于ParentCategory引用可以为null，我将如何在视图中显示？我有以下内容：

  @ Model.ParentCategory.Name 
  

..但是如果类别没有与其关联的父类别，它不会给出错误吗？如何在视图中显示？

解决方案

如果您需要访问子类别，可以向您的模型添加集合属性

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

然后您可以将模型设置为

  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。

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

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.

I followed this article on Code Project.

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; }
}

My context class:

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);
     }
}

Not sure if the above is correct?

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.

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

EDIT

This is how I retrieve my category:

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

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

@Model.ParentCategory.Name

..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?

解决方案

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; }
}

Then you can setup the model as

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

Edit

You should check whether ParentCategory is null or not.

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

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