使用方法澄清自定義Rails 3.0驗證

Question

我在Rails 3.0中創建了一個自定義驗證器，驗證列的組合是否在表中唯一。驗證的完整代碼是：

class UniqueInProjectValidator < ActiveModel::EachValidator 

    def validate_each(object, attribute, value) 
    unless object.class.where("project_id = ? AND #{attribute} = ?", object.project_id, value).empty? 
     if object.new_record? 
     object.errors[attribute] << (options[:message] || "must be unique in each project") 
     else 
     orig_rec = object.class.find(object.id) 
     if value != orig_rec.method(attribute).call || object.project_id != orig_rec.project_id 
      object.errors[attribute] << (options[:message] || "must be unique in each project") 
     end 
     end 
    end 

end 

請注意，這是不容易認識到什麼的if語句做的，所以我希望能夠與def attribute_and_project_exist?方法，第二if語句來代替unless條件採用def attribute_or_project_changed?方法。但是，在創建這些方法時，來自validates_each的參數因封裝而不通過。

現在的問題：是否有辦法以某種方式乾淨地允許我的兩個新創建的方法訪問這些變量，就像我們可以對模型中的列名所做的那樣，或者我堅持使用傳遞每個參數或者讓讀者難以閱讀條件陳述？

在此先感謝！

Answer 1

我想你可以清理有點用一個變量，一個拉姆達，和一個「儘快恢復」：

def validate_each(object, attribute, value) 
    # If there is no duplication then bail out right away as 
    # there is nothing to check. This reduces your nesting by 
    # one level. Using a variable here helps to make your 
    # intention clear. 
    attribute_and_project_exists = object.class.where("project_id = ? AND #{attribute} = ?", object.project_id, value).empty? 
    return unless attribute_and_project_exists 

    # This lambda wraps up your second chunk of ugly if-ness and saves 
    # you from computing the result unless you have to. 
    attribute_or_project_changed = lambda do 
    orig_rec = object.class.find(object.id) 
    value != orig_rec.method(attribute).call || object.project_id != orig_rec.project_id 
    end 

    # Note that || short-circuits so the lambda will only be 
    # called if you have an existing record. 
    if object.new_record? || attribute_or_project_changed.call 
    object.errors[attribute] << (options[:message] || "must be unique in each project") 
    end 
end 

我不知道要好上多少比你的原創，但邏輯和控制流程更清晰，由於更好的塊。