直接多对多映射仅在连接表只包含外键。如果您想要在连接表中公开其他属性，则必须将其映射到单独的实体，并将两个一对多关系映射到多对多使用的前实体。

我实际上不能写你的代码，因为我不明白你的例子。

只尝试（不要映射多对多用户）：

  modelBuilder.Entity< UserRelation> 
 .HasRequired（r => r.User）
 .WithMany（u => u.Followers）; 

 modelBuilder.Entity< UserRelation> 
 .HasRequired（r => r.Follower）
 .WithMany（）; 
 

We have legacy database and we map the new objects and props to the old tables and columns. So far so good. We have many-to-many relation which was mapped successfully. The intermediate table contains additional data. When we try to map the intermediate table to an object we get exception that the mapping is already defined. If we remove mapping from any side of the relation we get error that table is missing (ofc, we expect just that). I can do that easily with NHibernate and I am starting to think that EF is missing really really many features. So, please, tell me I am wrong and we can do that with EF.

Best regards

EDIT: here is a dummy sample which fails.

class User
{
  public ICollection<User> Followers{get;set;}
}

class UserRelation
{
  public User User{get;set;}
  public User Follower{get;set;}
  public DateTime CreatedOn{get;set;}
}

---

user mapping

modelBuilder
     .Entity<User>()
     .HasMany<User>(user => user.Followers)
     .WithMany()
     .Map(m =>m.MapLeftKey("user_id").MapRightKey("follower_id")
     .ToTable("user_follower"));

user relation mapping

modelBuilder
     .Entity<UserRelation>()
     .ToTable("user_follower");

modelBuilder
     .Entity<UserRelation>()
     .HasOptional<User>(f => f.User)
     .WithRequired().Map(m => m.MapKey("user_id"));

modelBuilder
     .Entity<UserRelation>()
     .HasOptional<User>(f => f.Follower)
     .WithRequired().Map(m => m.MapKey("follower_id"));

modelBuilder
     .Entity<UserRelation>()
     .Property(entity => entity.CreatedOn)
     .HasColumnName("created_on");

Exception

Schema specified is not valid. Errors: (67,6) : error 0019: The EntitySet 'UserUser' with schema 'dbo' and table 'user_follower' was already defined. Each EntitySet must refer to a unique schema and table.

Edit2: Here is another example of this model: http://learnentityframework.com/LearnEntityFramework/tutorials/many-to-many-relationships-in-the-entity-data-model/

Direct many-to-many mapping is available only if junction table contains just foreign keys. If you want to expose other properties in junction table you must map it to separate entity and mapt two one-to-many relations from former entities used in many-to-many.

I'm actually not able to write you the code because I don't understand your example.

Try only (don't map Many-to-many in User):

modelBuilder.Entity<UserRelation>
    .HasRequired(r => r.User)
    .WithMany(u => u.Followers);

modelBuilder.Entity<UserRelation>
    .HasRequired(r => r.Follower)
    .WithMany();