实体框架核心：与同一实体的多对多关系 [英] Entity Framework Core: many-to-many relationship with same entity

问题描述

我正在尝试将多对多关系与同一个实体进行映射。 用户实体具有 IList< User> 数据字段联系人，它存储用户的联系人/朋友信息：

I am trying to map many-to-many relationship with the same entity. The User entity has an IList<User> data field for Contacts, which stores user's contacts/friends information:

public class User : DomainModel
{
    public virtual IList<User> Contacts { get; protected set; }
    //irrelevant code omitted
}

当我尝试使用流利的API映射这么多关系很多，给我一些麻烦。显然，当我在 user.Contacts 属性中使用 HasMany（）时，它没有 WithMany（）方法调用next。 Visual Studio中的智能感知器只显示 WithOne（），但不显示 WithMany（）。

When I try to use fluent API to map this many to many relationship, it gives me some trouble. Apparently, when I use HasMany() on the user.Contacts property, it has no WithMany() method to call next. The intellisense from Visual Studio only shows WithOne(), but not WithMany().

modelBuilder.Entity<User>().HasMany(u => u.Contacts).WithMany() 
// gives compile time error: CS1061 'CollectionNavigationBuilder<User, User>' does not contain a definition for 'WithMany' and no extension method 'WithMany' accepting a first argument of type 

那么为什么会这样呢？是否有任何错误的地图映射这种多对多的关系？请帮忙。

So why does this happen? Is there anything I did wrong to map this many-to-many relationship? Please help.

推荐答案

那么为什么会发生这种情况？有没有什么我做错的地图这个
多对多关系？

So why does this happen? Is there anything I did wrong to map this many-to-many relationship?

不，你没有哪里不对了。 只是不支持。当前状态 here 。

No, you didn't do anything wrong. It's just not supported. Current status here.

尚未支持没有实体类来表示
连接表的多对多关系。然而，您可以通过为连接
表包含一个实体类来映射两个单独的一对多关系来代表
多对多关系。

Many-to-many relationships without an entity class to represent the join table are not yet supported. However, you can represent a many-to-many relationship by including an entity class for the join table and mapping two separate one-to-many relationships.

使用EF-Core，您应该为映射表创建实体。例如 UserContacts 。 docs 中的完整示例，作为在评论中提到。我没有实际测试下面的代码，但它应该看起来像这样：

With EF-Core you should create the entity for the mapping table. Such as UserContacts. A complete example in the docs, as mentioned in the comments. I haven't actually tested the code below, but it should look something like this:

public class UserContacts
{
    public int UserId { get; set; } 
    public virtual User User { get; set; }

    public int ContactId { get; set; } // In lack of better name.
    public virtual User Contact { get; set; }
}

public class User : DomainModel
{
    public List<UserContacts> Contacts { get; set; }
}

而您的 modelBuilder 。

  modelBuilder.Entity<UserContacts>()
        .HasOne(pt => pt.Contact)
        .WithMany(p => p.Contacts)
        .HasForeignKey(pt => pt.ContactId);

    modelBuilder.Entity<UserContacts>()
        .HasOne(pt => pt.User)
        .WithMany(t => t.Contacts)
        .HasForeignKey(pt => pt.UserId);

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