抛出NoMethodError的belongs_to / has_many关联：未定义的方法

Question

我的代码有3个模型，所有模型都具有一个fors_to / has_many关联。 当我尝试使用Rails控制台在视图中从对象的关联表中提取表时，抛出NoMethodError。

有问题的模型：

class Coin < ActiveRecord::Base
  # If coin is destroyed, so is their market prices
  has_many :market_prices, dependent: :destroy
  has_many :networks, dependent: :destroy
end

class MarketPrice < ActiveRecord::Base
  belongs_to :coin
end

class Network < ActiveRecord::Base
  belongs_to :coin
end

Rails控制台：

2.0.0-p247 :004 > Coin.find_by_tag("btc").networkhashrate                                                          Coin Load (0.3ms)  SELECT "coins".* FROM "coins" WHERE "coins"."tag" = 'btc' LIMIT 1                                                                                                                     
NoMethodError: undefined method `networkhashrate' for #<Coin:0x00000005b15030>                                                                                                                             
        from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/activemodel-4.0.0/lib/active_model/attribute_methods.rb:436:in `method_missing'                                                                   
        from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.0/lib/active_record/attribute_methods.rb:131:in `method_missing'                                                                 
        from (irb):4                                                                                                                                                                                       
        from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands/console.rb:90:in `start'                                                                                        
        from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands/console.rb:9:in `start'                                                                                         
        from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands.rb:64:in `<top (required)>'                                                                                     
        from bin/rails:4:in `require'                                                                                                                                                                      
        from bin/rails:4:in `<main>'   

另一个例子：

2.0.0-p247 :005 > coin = Coin.first                                                                                                                                                                        
  Coin Load (0.3ms)  SELECT "coins".* FROM "coins" ORDER BY "coins"."id" ASC LIMIT 1                                                                                                                       
 => #<Coin id: 1, created_at: "2014-04-02 02:44:01", updated_at: "2014-04-02 02:44:01", tag: "10-5", name: "10-5", website: "">                                                                            
2.0.0-p247 :006 > coin.coin_id                                                                                                                                                                             
NoMethodError: undefined method `coin_id' for #<Coin:0x00000005b1c920>                                                                                                                                     
        from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/activemodel-4.0.0/lib/active_model/attribute_methods.rb:436:in `method_missing'                                                                   
        from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/activerecord-4.0.0/lib/active_record/attribute_methods.rb:131:in `method_missing'                                                                 
        from (irb):6                                                                                                                                                                                       
        from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands/console.rb:90:in `start'                                                                                        
        from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands/console.rb:9:in `start'                                                                                         
        from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands.rb:64:in `<top (required)>'                                                                                     
        from bin/rails:4:in `require'                                                                                                                                                                      
        from bin/rails:4:in `<main>' 

Schema.rb：

ActiveRecord::Schema.define(version: 20140402005453) do

  create_table "coins", force: true do |t|
    t.datetime "created_at"
    t.datetime "updated_at"
    t.string   "tag"
  end

  create_table "market_prices", force: true do |t|
    t.datetime "created_at"
    t.datetime "updated_at"
    t.integer  "coin_id"        
  end

  create_table "networks", force: true do |t|
    t.integer  "networkhashrate"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.integer  "coin_id"
  end

end

我无法朝任一方向走。 示例：Coin.find_by_tag（“ btc”）。networkhashrate或Network.find_by_coin_id（“ 83”）。tag

我在编写的另一个应用程序中几乎都具有与示例相同的设置，并且效果很好。 我已经重新加载了Rails控制台/重新启动了我的开发环境。 为什么Rails看不到我的联系？

感谢您抽出时间来阅读。

Answer 1

Coin.find_by_tag("btc").networkhashrate

Coin.find_by_tag返回硬币。 硬币没有称为networkhashrate的方法，而网络却有。

---

Network.find_by_coin_id("83").tag

Network.find_by_coin_id返回一个网络。 网络没有称为tag的方法，硬币没有。