多对多映射表

Question

从我在网上和编程实体框架CodeFirst一书中看到的例子中,当你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.

但是,当我执行下面的操作时,我会在Recipes表中调用一个新字段,Member_Id并Recipe_Id在Members表中创建一个字段.

这只会创建两个一对多关系,但不会产生多对多关系,所以我可以将成员3链接到食谱(4,5,6)和配方4链接到成员(1,2,3)等.

有没有办法创建这个映射表？如果是这样,你如何命名其他东西,如"烹饪书"？

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; }
    }

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,我也将以下示例重命名为Cookbooksto MembersRecipes,这也修复了我的问题,类似于答案,但如上所述进一步的影响

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; }
}

在Recipe&Memberclasses中我将集合更改为

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

Answer 1

在你的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");
    });
}

你可以反过来做它,它是相同的,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");
});

更多例子:

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

UPDATE

要防止对作者属性进行周期性引用,除此之外,您需要添加以下内容:

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

想法来源于此:EF Code First具有多对多的自引用关系

核心问题是,您需要告知EF Author属性(它是一个Member实例)没有Recipe集合(表示为WithMany()); 这样,可以在作者属性上停止循环引用.

这些是上面Code First映射中创建的表:

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)
);