Question

我有这个协会：

user.rb

class User < ActiveRecord::Base
  has_many :todo_lists
  has_one :profile
end

todo_list.rb

class TodoList < ActiveRecord::Base
  belongs_to :user
end

profile.rb

class Profile < ActiveRecord::Base
  belongs_to :user
end

我试图理解以下行为：

todo_list = TodoList.create(name: "list 1")

todo_list.create_user(username: "foo")

todo_list.user
#<User id: 1, username: "foo", created_at: "2016-05-01 07:09:05", updated_at: "2016-05-01 07:09:05">

test_user = todo_list.user

test_user.todo_lists # returns an empty list
=> #<ActiveRecord::Associations::CollectionProxy []>

test_user.todo_lists.create(name: "list 2")

test_user.todo_lists
=> #<ActiveRecord::Associations::CollectionProxy [#<TodoList id: 2, name: "list 2", user_id: 1, created_at: "2016-05-01 07:15:13", updated_at: "2016-05-01 07:15:13">]>

为什么#create_user将user添加到todo_list（todo_list.user会返回user），但在user.todo_lists被调用时不反映关联？

已编辑：

使用belongs_to时，尝试在one-to-one关系中从#create_user!侧创建记录。在belongs_to关系中one-to-many创建记录时，即使使用#create_user!，它仍然不成立。

profile = Profile.create(first_name: "user_one")

profile.create_user!(username: "user_one username")

profile.user
=> #<User id: 6, username: "user_one username", created_at: "2016-05-01 18:22:31", updated_at: "2016-05-01 18:22:31">

user_one = profile.user
=> #<User id: 6, username: "user_one username", created_at: "2016-05-01 18:22:31", updated_at: "2016-05-01 18:22:31">

user_one.profile # the relationship was created
=> #<Profile id: 2, first_name: "user_one", user_id: 6, created_at: "2016-05-01 18:22:09", updated_at: "2016-05-01 18:22:31">

todo_list = TodoList.create(name: "a new list")

todo_list.create_user!(username: "user of a new list")

todo_list.user
=> #<User id: 7, username: "user of a new list", created_at: "2016-05-01 18:26:27", updated_at: "2016-05-01 18:26:27">

user_of_new_list = todo_list.user
=> #<User id: 7, username: "user of a new list", created_at: "2016-05-01 18:26:27", updated_at: "2016-05-01 18:26:27">

user_of_new_list.todo_lists #still does not create user from todo_list
=> #<ActiveRecord::Associations::CollectionProxy []>

Answer 1

我想你忘了保存todo_list。创建用户不会自动保存todo_list，TodoList的外键不是User（todo_list.user_id）。

如何从belongs_to关联创建记录？

1 个答案: