Question

我在Rails设置中遇到了一个奇怪的问题，这让我感到困惑。我试图在用户和图书之间创建以下关系

class Book < ActiveRecord::Base   
  has_many :follows, :dependent => :destroy
  belongs_to :user
end

class Follow < ActiveRecord::Base
  attr_accessible :user_id,
                  :book_id,
                  :updated_at
  belongs_to :user
  belongs_to :book_id
  validates :user_id, presence: true
  validates :book_id, presence: true
end

class User < ActiveRecord::Base   
  has_many :books, :dependent => :destroy
  has_many :follows, :dependent => :destroy
end

直观地说，用户可以拥有多本书籍，并且可以关注其他书籍（来自其他用户）我希望我的Follow模型能够跟踪这种关系

以下是我的数据库设置方式（PostgreSQL）

# \d follows
                                     Table "public.follows"
   Column   |            Type             |                      Modifiers                       
------------+-----------------------------+------------------------------------------------------
 id         | integer                     | not null default nextval('follows_id_seq'::regclass)
 user_id    | integer                     | 
 book_id    | integer                     | 
 created_at | timestamp without time zone | 
 updated_at | timestamp without time zone | 
Indexes:
    "follows_pkey" PRIMARY KEY, btree (id)
    "index_follows_on_book_id_and_user_id" UNIQUE, btree (book_id, user_id)
    "index_follows_on_book_id" btree (book_id)
    "index_follows_on_user_id" btree (user_id)

最后，当我打开Rails控制台并尝试创建Follow实例并分配book_id值时，它会在标题中吐出消息：

rails c 加载开发环境（Rails 4.0.0.rc1） 2.0.0p247：001＆gt; f = Follow.new =＆GT; ＃ 2.0.0p247：004＆gt; f.book_id = 48 NameError：未初始化的常量Follow :: BookId 来自/Users/minghuazhao/.rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.0.rc1/lib/active_record/inheritance.rb:125:in compute_type' from /Users/minghuazhao/.rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.0.rc1/lib/active_record/reflection.rb:178:in klass＆＃39; 来自/Users/minghuazhao/.rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.0.rc1/lib/active_record/associations/association.rb:207:in raise_on_type_mismatch!' from /Users/minghuazhao/.rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.0.rc1/lib/active_record/associations/belongs_to_association.rb:11:in替换＆＃39 ; 来自/Users/minghuazhao/.rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.0.rc1/lib/active_record/associations/singular_association.rb:17:in writer' from /Users/minghuazhao/.rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.0.rc1/lib/active_record/associations/builder/association.rb:78:in book_id =＆＃39; 来自（irb）：4 来自/Users/minghuazhao/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0.rc1/lib/rails/commands/console.rb:90:in start' from /Users/minghuazhao/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0.rc1/lib/rails/commands/console.rb:9:in start＆＃39 ; 来自/Users/minghuazhao/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0.rc1/lib/rails/commands.rb:66:in <top (required)>' from bin/rails:4:in要求＆＃39; 来自bin / rails：4：在`＆＃39;

如果有人能说出正在发生的事情并给出一些提示，那就太棒了。提前谢谢。

Answer 1

更改：

belongs_to :book_id

到

belongs_to :book

另外，您真的希望将book_id和user_id标记为可访问吗？这可能允许使用精心设计的帖子请求更新这些字段。

NameError：未初始化的常量<model>：<column_name> </column_name> </model>

1 个答案: