多对多映射表 [英] Many-to-many mapping table
问题描述
从我在网上看到的示例和编程实体框架CodeFirst的书中，当您有两个类的集合时，EF将创建一个映射表，如 MembersRecipes 和每个类的主键将链接到此表。
但是，当我执行以下操作时，我会在 Recipes 表$ code> Member_Id 和 Recipe_Id 在成员 table。
哪些只创建两个一对多的关系，但不是一对多的关系，所以我可以把会员3链接到食谱（ 4,5）和配方4链接到会员（1,2,3）等。
有没有办法创建这个映射表？如果是这样，你如何命名其他的东西，如cookbooks？
谢谢
public abstract class Entity {
[必需]
public int Id {get;组;
}
public class成员：Entity {
[必需]
public string Name {get;组; }
public virtual IList< Recipe>食谱{get;组;
}
public class配方：Entity {
[必需]
public string Name {get;组; }
[ForeignKey（Author）]
public int AuthorId {get;组; }
public virtual Member作者{get;组; }
....
public virtual IList< Member>会员{get;组;
}
更新：
以下是另一种方法我已经尝试了不使用Fluent API并替换 AuthorId & 作者在食谱中拥有所有者标志，我也将以下示例从 Cookbooks 到 MembersRecipes ，这也解决了我的问题类似于答案，但是如上所述还有其他的影响。
[ForeignKey（Recipe）]
[Key，Column（Order = 0） public int RecipeId {get;组; }
public virtual配方食谱{get;组;
[Key，Column（Order = 1）]
[ForeignKey（Member）]
public int MemberId {get;组; }
public virtual Member Member {get;组; }
public bool Owner {get;组; }
}
和配方& 会员课程我将集合更改为
public virtual IList< MembersRecipes> MembersRecipes {get;组;
在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）; //第三个表命名为Cookbooks
x.MapLeftKey（RecipeId）;
x.MapRightKey（MemberId）;
}）;
}
你可以这样做，相同，只是另一个相同硬币的一边：
modelBuilder.Entity< Member>（）
.HasMany（x => x .Recipes）
.WithMany（x => x.Members）
.Map（x =>
{
x.ToTable（Cookbooks）; //第三表名为Cookbooks
x.MapLeftKey（MemberId）;
x.MapRightKey（RecipeId）;
}）;
其他示例：
http://www.ienablemuch.com/2011/07/using-checkbox-list-on-aspnet-mvc-with_16.html
< a href =http://www.ienablemuch.com/2011/07/nhibernate-equivalent-of-entity.html =nofollow noreferrer> http://www.ienablemuch.com/2011/07/nhibernate -equivalent-of-entity.html
更新
为了防止您的作者财产的周期性引用，除了上述之外，您需要添加以下内容：
code> modelBuilder.Entity< Recipe>（）
.HasRequired（x => x.Author）
.WithMany（）
.WillCascadeOnDelete（false）;
这里提供的想法： EF Code First with many to many self referenceing relationship
核心的是，您需要通知EF，作者属性（它是一个成员实例）没有配方集合（由 WithMany（）表示）;这样，可以在作者属性上停止循环引用。
这些是从上面代码第一个映射创建的表：
$ b code $ c CREATE TABLE成员（
id int IDENTITY（1,1）NOT NULL主键，
名称nvarchar（128）NOT NULL
） ;
CREATE TABLE配方（
ID int IDENTITY（1,1）NOT NULL主键，
名称nvarchar（128）NOT NULL，
AuthorId int NOT NULL references成员（Id）
）;
CREATE TABLE Cookbooks（
RecipeId int NOT NULL，
MemberId int NOT NULL，
constraint pk_Cookbooks主键（RecipeId，MemberId）
）;
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 MembersRecipes and the primary key from each class would link to this table.
However when I do the below, I instead get a new field in the Recipes table called Member_Id and a Recipe_Id in the Members table.
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.
Is there a way to create this mapping table? and if so how do you name it something else such as "cookbooks" ?
Thanks
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 & Author on Recipe with an owner flag, I have also renamed the below example from Cookbooks to MembersRecipes, this also fixes my issue similar to the answer but as mentioned has further implications.
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 & Member classes I changed the collections to
public virtual IList<MembersRecipes> MembersRecipes { get; set; }
Do this on your DbContext OnModelCreating:
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:
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:
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
To prevent cyclical reference on your Author property, aside from above, you need to add this:
modelBuilder.Entity<Recipe>()
.HasRequired(x => x.Author)
.WithMany()
.WillCascadeOnDelete(false);
Idea sourced here: EF Code First with many to many self referencing relationship
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.
These are the created tables from the Code First mappings above:
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)
);
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