EF代码优先 - WithMany（） [英] EF Code First - WithMany()

问题描述

最近，我由类 ManyNavigationPropertyConfiguration< TEntity，TTarget>
，那班上有中，我发现了一个名为方法 WithMany （）与2重载

I recently came by the class ManyNavigationPropertyConfiguration<TEntity, TTarget> , and within that class there I found a method named WithMany() with 2 overloads.

第一个过载：
WithMany（）

配置的关系为
许多：许多不上的另一侧的导航
属性
的关系。

Configures the relationship to be many:many without a navigation property on the other side of the relationship.

第二个重载：
WithMany（表达式来; Func键< TTarget ，ICollection的< TEntity>>>）

配置的关系是
多方面的：多用在关系的另一端的导航属性

Configures the relationship to be many:many with a navigation property on the other side of the relationship.

现在是我的问题，你为什么会配置关系是多方面的：许多人没有导航属性（第一个过载）？我没有看到任何场景中，这将是有益的...任何想法

Now is my question, why would you configure a relationship to be many:many without a navigation property (the first overload)? I dont see any scenarios where that would be helpful... Any thoughts?

推荐答案

一个例子可能是这种模式：

An example might be this model:

public class User
{
    public int UserId { get; set; }
    public string Name { get; set; }
    public ICollection<Role> Roles { get; set; }
}

public class Role
{
    public int RoleId { get; set; }
    public string Description { get; set; }
}

如果你永远不会有兴趣来获取这是在所有用户特定角色后，加入了导航属性...

If you are never interested to retrieve all users which are in a specific role, adding a navigation property ...

public ICollection<User> Users { get; set; }

...到角色类是不必要的开销。

但你还是必须EF告诉一个多到很多用户之间的关系和角色存在...

But you still must EF tell that a many-to-many relationship between User and Role exists ...

modelBuilder.Entity<User>()
            .HasMany(u => u.Roles)
            .WithMany();

...因为默认公约映射将产生一个错误的关系，即一对多关系，对应的映射：

... because the default convention mappings would create a wrong relationship, namely a one-to-many relationship, corresponding to this mapping:

modelBuilder.Entity<User>()
            .HasMany(u => u.Roles)
            .WithOptional();

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