C# 多对多映射表

Many-to-many mapping table

提问by Pricey

From examples that I have seen online and in a Programming Entity Framework CodeFirst book, when you have a collection on both classes EF would create a mapping table such as MembersRecipesand the primary key from each class would link to this table.

根据我在网上和编程实体框架 CodeFirst 书中看到的示例，当您在两个类上都有一个集合时，EF 将创建一个映射表，例如MembersRecipes每个类的主键将链接到该表。

However when I do the below, I instead get a new field in the Recipestable called Member_Idand a Recipe_Idin the Memberstable.

然而，当我做下面的，我不是在得到一个新的领域Recipes称为表Member_Id和Recipe_Id在Members表中。

Which only creates two one-to-many relationships, but not a many-to-many so I could have Member 3 linked to Recipes (4,5,6) and Recipe 4 linked to Members (1,2,3) etc.

这只会创建两个一对多关系，而不是多对多关系，因此我可以将成员 3 链接到食谱 (4,5,6) 并将食谱 4 链接到成员 (1,2,3) 等。

Is there a way to create this mapping table? and if so how do you name it something else such as "cookbooks" ?

有没有办法创建这个映射表？如果是这样，您如何命名它，例如“食谱”？

Thanks

谢谢

    public abstract class Entity {
        [Required]
        public int Id { get; set; }
    }   

    public class Member : Entity {
        [Required]
        public string Name { get; set; }

        public virtual IList<Recipe> Recipes { get; set; }
    }

    public class Recipe : Entity {  
        [Required]
        public string Name { get; set; }

        [ForeignKey("Author")]
        public int AuthorId { get; set; }
        public virtual Member Author { get; set; }

            ....

        public virtual IList<Member> Members { get; set; }
    }

UPDATE:Below is another approach I have tried which doesn't use the Fluent API and replaces the AuthorId& Authoron Recipewith an owner flag, I have also renamed the below example from Cookbooksto MembersRecipes, this also fixes my issue similar to the answer but as mentioned has further implications.

更新：下面是我尝试过的另一种方法，它不使用 Fluent API 并用所有者标志替换AuthorId& Authoron Recipe，我还将下面的示例从Cookbooksto重命名MembersRecipes，这也解决了我的问题，类似于答案，但如前所述进一步的影响。

public class MembersRecipes {

    [Key, Column(Order = 0)]
    [ForeignKey("Recipe")]
    public int RecipeId { get; set; }
    public virtual Recipe Recipe { get; set; }

    [Key, Column(Order = 1)]
    [ForeignKey("Member")]
    public int MemberId { get; set; }
    public virtual Member Member { get; set; }

    public bool Owner { get; set; }
}

and in Recipe& Memberclasses I changed the collections to

在Recipe&Member类中，我将集合更改为

public virtual IList<MembersRecipes> MembersRecipes { get; set; }

采纳答案by Michael Buen

Do this on your DbContext OnModelCreating:

在您的 DbContext OnModelCreating 上执行此操作：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{    
    modelBuilder.Entity<Recipe>()
        .HasMany(x => x.Members)
        .WithMany(x => x.Recipes)
    .Map(x =>
    {
        x.ToTable("Cookbooks"); // third table is named Cookbooks
        x.MapLeftKey("RecipeId");
        x.MapRightKey("MemberId");
    });
}

You can do it the other way around too, it's the same, just another side of the same coin:

你也可以反过来做，它是一样的，只是同一枚硬币的另一面：

modelBuilder.Entity<Member>()
    .HasMany(x => x.Recipes)
    .WithMany(x => x.Members)
.Map(x =>
{
  x.ToTable("Cookbooks"); // third table is named Cookbooks
  x.MapLeftKey("MemberId");
  x.MapRightKey("RecipeId");
});

---

---

Further examples:

进一步的例子：

http://www.ienablemuch.com/2011/07/using-checkbox-list-on-aspnet-mvc-with_16.html

http://www.ienablemuch.com/2011/07/using-checkbox-list-on-aspnet-mvc-with_16.html

http://www.ienablemuch.com/2011/07/nhibernate-equivalent-of-entity.html

http://www.ienablemuch.com/2011/07/nhibernate-equivalent-of-entity.html

---

---

UPDATE

更新

To prevent cyclical reference on your Author property, aside from above, you need to add this:

为了防止对您的 Author 属性进行循环引用，除上述之外，您还需要添加以下内容：

modelBuilder.Entity<Recipe>()
    .HasRequired(x => x.Author)
    .WithMany()
    .WillCascadeOnDelete(false);

Idea sourced here: EF Code First with many to many self referencing relationship

想法来源于此处：EF Code First 具有多对多自引用关系

The core thing is, you need to inform EF that the Author property(which is a Member instance) has no Recipe collections(denoted by WithMany()); that way, cyclical reference could be stopped on Author property.

核心是，您需要通知 EF Author 属性（它是一个 Member 实例）没有 Recipe 集合（由 表示WithMany()）；这样，可以在 Author 属性上停止循环引用。

These are the created tables from the Code First mappings above:

这些是从上面的 Code First 映射创建的表：

CREATE TABLE Members(
    Id int IDENTITY(1,1) NOT NULL primary key,
    Name nvarchar(128) NOT NULL
);


CREATE TABLE Recipes(
    Id int IDENTITY(1,1) NOT NULL primary key,
    Name nvarchar(128) NOT NULL,
    AuthorId int NOT NULL references Members(Id)
);


CREATE TABLE Cookbooks(
    RecipeId int NOT NULL,
    MemberId int NOT NULL,
    constraint pk_Cookbooks primary key(RecipeId,MemberId)
);