ASP.NET MVC 多对多关系，使用“我自己的"桌子

问题描述

我对在实体框架中使用 Code First 方法相当陌生，而且我知道我与下面的实体有多对多关系，EF 将自动创建中间表:

I am fairly new to using Code First approach with entity framework and I know that I you have a many to many relationship like the entities below, the EF will create the intermediary table automatically:

class Post {
  ...
  public virtual ICollection<Category> Categories {get; set;}
  ...
}

class Category {
   ...
   public virtual ICollection<Post> Posts {get; set;}
   ...
}

但是，如果在中间表中我需要有额外的数据字段，一种可能的方法(我目前喜欢，也许是因为我不知道更好的方法)是定义我自己的新实体，例如:

However, if in the intermediary table I need to have extra data fields, one possible way (which I currently like, maybe because I am unaware of better ways) would be defining a new Entity of my own, like:

class Posts_Categories {
   public int Id {get; set;}
   public int CategoryId {get; set;}
   public int PostId {get; set;}
   public string Exrtafield1 {get; set;}
   public int ex extraField2 {get; set;}
   ...
   public virtual Post Post {get; set;}
   public virtual Category Category {get; set;}
}

使用这种方法，EF 确实创建了我的自定义中间表，但它也创建了另一个名为PostsCategories"的自己的中间表，它只包含一个指向 Post_Id 的外键和另一个指向 Category_Id 的外键.

Using this approach, EF does create my custom intermediary table, but it also creates another one of its own called "PostsCategories" which only contains a foreign key to Post_Id and another to Category_Id.

如何让它不创建额外的一个并使用我定义的那个?这是管理具有额外数​​据字段的多对多关系的好方法吗?

How do I make it not create that extra one and use the one I have defined?Is this a good way to manage Many to Many relationships with extra data fields??

推荐答案

你应该像这样使用一对多关系:

you should use one to many relation like this :

public class Post
{
    public System.Int32 PostId { get; set; }

    [InverseProperty("Post")]
    public virtual ICollection<Posts_Category> PostCategories { get; set; }
}

public class Category
{
    public System.Int32 CategoryId { get; set; }

    [InverseProperty("Category")]
    public virtual ICollection<Posts_Category> PostCategories { get; set; }
}

public class Posts_Category
{
    public System.Int32 PostId { get; set; }

    public System.Int32 CategoryId { get; set; }

    [ForeignKey("PostId")]
    [InverseProperty("PostCategories")]
    public virtual Post Post { get; set; }

    [ForeignKey("CategoryId")]
    [InverseProperty("PostCategories")]
    public virtual Category Category { get; set; }
}

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