c# - 如何通过实体键添加/删除与 Entity Framework 的多对多关系？

Question

我试过:

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();
}

在未抛出异常但未删除关系之前尝试使用 Remove() 而不调用 attach 时。

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 Stub Entities(如上述用户)比使用 EntityKeys 更容易。

查看此 blog post有关 stub 实体技术的更多信息。

希望对你有帮助

亚历克斯