如何通过实体键添加/删除与实体框架的多对多关系？

Question

我尝试过：

using (Entities e = new Entities())
{
    EntityKey key = new EntityKey("Entities.Users", "UserId", 20);
    User user = new User { EntityKey = key};
    Role role = e.Roles.FirstOrDefault();
    //role.Users.Attach(user); //throws (when uncommented...) InvalidOperationException:
    //The object being attached to the source object is not attached to the same ObjectContext as the source object.
    role.Users.Add(user); //throws InvalidOperationException too:
    //The object cannot be added to the ObjectStateManager because it already has an EntityKey. Use ObjectContext.Attach to attach an object that has an existing key.
    e.SaveChanges();
}

当尝试使用Remove()而不调用attach之前，没有抛出异常但关系未删除。

Answer 1

尝试这样的事情：

User user = new User {UserId = 20};
e.AttachTo("Users", user);
Role role = e.Roles.FirstOrDefault();
role.Users.Add(user);
e.SaveChanges();

我发现使用存根实体（如上面的用户）比使用 EntityKey 更容易。

请参阅此 博客文章了解有关存根实体技术的更多信息。

希望这对

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