通過導軌協會查詢

我無法讓我的模型關聯，或者我不知道如何通過關聯進行查詢。通過導軌協會查詢

class Entry < ActiveRecord::Base 
    has_one :category 
end 

class Category < ActiveRecord::Base 
    belongs_to :entry 
end

現在，如果我進入我的鐵軌控制檯，並要求Entry.first，我得到：

Entry Load (0.1ms) SELECT "entries".* FROM "entries" LIMIT 1 
=> #<Entry id: 1, category_id: 1, duration: 2.0, image: "3", note: "4", url: "5", created_at: "2012-03-03 02:22:23", updated_at: "2012-03-03 02:22:23">

，如果我問Category.first因爲我得到：

Category Load (0.1ms) SELECT "categories".* FROM "categories" LIMIT 1 
=> #<Category id: 1, name: "Dev", created_at: "2012-03-03 02:17:17", updated_at: "2012-03-03 02:17:17">

但是，如果我請求Entry.first.category.name，它中斷，我得到：

Entry Load (0.1ms) SELECT "entries".* FROM "entries" LIMIT 1 
NoMethodError: undefined method `category' for #<Entry:0x007fec4d217848> 
from /Users/john/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/activemodel-3.2.1/lib/active_model/attribute_methods.rb:407:in `method_missing' 
from /Users/john/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/activerecord-3.2.1/lib/active_record/attribute_methods.rb:126:in `method_missing' 
from (irb):63 
from /Users/john/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/railties-3.2.1/lib/rails/commands/console.rb:47:in `start' 
from /Users/john/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/railties-3.2.1/lib/rails/commands/console.rb:8:in `start' 
from /Users/john/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/railties-3.2.1/lib/rails/commands.rb:41:in `<top (required)>' 
from script/rails:6:in `require' 
from script/rails:6:in `<main>'

這是爲什麼？如何通過條目獲取該類別的名稱？我究竟做錯了什麼？

來源

2012-03-03 John

在你的情況一個分類表應該有entry_id列，但你有category_id在條目一。

所以嘗試改變：

class Entry < ActiveRecord::Base 
    belongs_to :category 
end 

class Category < ActiveRecord::Base 
    has_one :entry 
end

或更改數據庫架構。

來源

2012-03-03 06:31:50

謝謝。我試了兩個方向，但沒有意識到我需要重新加載模型更改後的軌道控制檯。現在我明白了！ :) – John 2012-03-03 07:00:44

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