爲什麼沒有.build在rails控制檯中工作？

我正在構建和測試兩種模型的關聯：用戶，帖子。本質上，一個用戶只有一個用戶，但一個用戶has_many帖子，但一個帖子belongs_to。爲什麼沒有.build在rails控制檯中工作？

這就是說，我似乎無法得到User.first.posts.build的工作。我不斷返回一個錯誤。

**作爲一個問題，爲什麼User_id在Post模型中大寫？在我見過的大多數例子中，事實並非如此。當不大寫，它運行此錯誤：

Post.create(comment: "yolo molo tolo", user_id: 1) 
ActiveRecord::UnknownAttributeError: unknown attribute: user_id

CODE

（1）user.rb

class User < ActiveRecord::Base 
    validates :username, presence: true, length: { minimum: 6, maximum: 40} 
    has_many :posts 
end

（1）create_users.rb

class CreateUsers < ActiveRecord::Migration 
    def change 
    create_table :users do |t| 
     t.string :username 
     t.timestamps 
    end 
    end 
end

（ 3）Post.rb

class Post < ActiveRecord::Base 
    belongs_to :User 
    validates :comment, presence: true, length: { minimum: 5, maximum: 30 } 
end

（4）create_posts.rb

class CreatePosts < ActiveRecord::Migration 
    def change 
    create_table :posts do |t| 
     t.string :comment 
     t.references :User, index: true 

     t.timestamps 
    end 
    end 
end

錯誤

p3 = User.first.posts.new 
    User Load (0.2ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT 1 
ActiveRecord::UnknownAttributeError: unknown attribute: user_id 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/attribute_assignment.rb:47:in `rescue in _assign_attribute' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/attribute_assignment.rb:42:in `_assign_attribute' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/attribute_assignment.rb:29:in `block in assign_attributes' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/attribute_assignment.rb:23:in `each' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/attribute_assignment.rb:23:in `assign_attributes' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/associations/association.rb:178:in `initialize_attributes' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/associations/association.rb:251:in `block in build_record' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/core.rb:187:in `initialize' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/inheritance.rb:27:in `new' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/inheritance.rb:27:in `new' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/reflection.rb:189:in `build_association' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/associations/association.rb:250:in `build_record' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/associations/collection_association.rb:114:in `build' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/activerecord-4.0.3/lib/active_record/associations/collection_proxy.rb:229:in `build' 
    from (irb):19 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/railties-4.0.3/lib/rails/commands/console.rb:90:in `start' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/railties-4.0.3/lib/rails/commands/console.rb:9:in `start' 
    from /Users/MightyMouse/.rvm/gems/ruby-2.0.0-p353/gems/railties-4.0.3/lib/rails/commands.rb:62:in `<top (required)>' 
    from bin/rails:4:in `require'

來源

2014-04-01 funfuntime

如果返回「錯誤」，那麼請**，發佈錯誤**。我們仍然猜測可能會出現什麼問題。 – tadman

'user_id'在哪裏大寫爲'User_id'？ – vee

您的數據庫模式是否與您的遷移相匹配以進行評論？是否可以編輯遷移並且不重新運行？ – Shadwell

Post模型缺少user_id的屬性，至少這是你的錯誤意味着什麼。

rails g migration add_user_to_posts user:belongs_to 
rake db:migrate

你遷移文件顯示你在職位表中的用戶ID，但它可能以dB爲單位丟失，如果你沒有運行遷移。

作爲速戰速決，如果你不在乎安博在DB你的數據，我會跑：

rake db:reset

或者

rake db:drop db:create db:migrate

來源

2014-04-01 22:31:10 rmagnum2002

感謝您的想法..我嘗試'rake db：reset'，但仍然得到相同的錯誤。我也嘗試過'rails g migration add_user_to_posts..'。這似乎也不起作用。我認爲Post模型可以通過'rails g model來獲得user_id屬性。發表評論：字符串用戶：引用' – funfuntime

@KevinC'rails g模型發表評論：字符串用戶：引用'。它應該是'用戶：參考'不'用戶：參考' – Abednego

@Abednego，很好的發現，昨晚看不到錯誤。你是對的，應該是't.references：user，index：true'。 – rmagnum2002

爲什麼沒有.build在rails控制檯中工作？

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