Ruby on rails - where子句在關係上產生'undefined method'錯誤

Question

我有一個模型Email_address屬於用戶。而在我的用戶模型中，它表示has_many email_addresses。請看下面的控制檯輸出：

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irb(main):073:0>b = EmailAddress.find(2)

EmailAddress Load (0.4ms) SELECT email_addresses.* FROM email_addresses WHERE email_addresses.id = 2 LIMIT 1

=> #EmailAddress id: 2, email: "w@example.com", user_id: 2, created_at: "2013-03-06 02:33:40", updated_at: "2013-03-06 02:33:40"

irb(main):074:0>b.user

User Load (0.1ms) SELECT users.* FROM users WHERE users.id = 2 LIMIT 1

=> #User id: 2, username: "w", created_at: "2013-03-06 02:33:40", updated_at: "2013-03-06 02:33:40"

irb(main):075:0>b = EmailAddress.where(:email => "r@example.com")

EmailAddress Load (0.1ms) SELECT email_addresses.* FROM email_addresses WHERE email_addresses.email = r@example.com

=> #EmailAddress id: 1, email: "r@example.com", user_id: 1, created_at: "2013-03-05 07:26:56", updated_at: "2013-03-05 07:26:56"

irb(main):076:0>b.user

NoMethodError: undefined method user for # from /var/lib/gems/1.8/gems/activerecord-3.2.11/lib/active_record/relation/delegation.rb:45:in `method_missing' from (irb):76

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誰能告訴我，爲什麼當我使用where()我無法再找到用戶，但它的作品，當我使用find（）方法？這是非常令人困惑的輸出。

Answer 1

.where()返回數組（具體爲ActiveRecord::Relation）。要選擇返回的對象，您需要指定哪個對象。在這種情況下，因爲你希望一個對象，你可以這樣做：

b = EmailAddress.where(:email => "r@example.com").first 

OR

b = EmailAddress.where(:email => "r@example.com")[0]