Rails 3 中的作用域与类方法 [英] Scopes vs class methods in Rails 3

问题描述

作用域只是语法糖，还是使用它们与使用类方法相比有什么真正的优势?

Are scopes just syntax sugar, or is there any real advantage in using them vs using class methods?

一个简单的例子如下.据我所知，它们是可以互换的.

A simple example would be the following. They're interchangeable, as far as I can tell.

scope :without_parent, where( :parent_id => nil )

# OR

def self.without_parent
  self.where( :parent_id => nil )
end

每种技术更适合什么?

编辑

named_scope.rb 提到了以下(如下面的 goncalossilva 指出):

named_scope.rb mentions the following (as pointed out below by goncalossilva):

行 54:

请注意，这只是语法"用于定义实际类的糖方法

Note that this is simply 'syntactic sugar' for defining an actual class method

行 113:

命名范围也可以有扩展名，就像 has_many 声明一样:

Named scopes can also have extensions, just as with has_many declarations:

class Shirt < ActiveRecord::Base
  scope :red, where(:color => 'red') do
    def dom_id
      'red_shirts'
    end
  end
end

推荐答案

对于简单的用例，人们可以将其视为语法糖.然而，还有一些差异不止于此.

For simple use cases, one can see it as just being syntax sugar. There are, however, some differences which go beyond that.

例如，一个是在范围内定义扩展的能力:

One, for instance, is the ability to define extensions in scopes:

class Flower < ActiveRecord::Base
  named_scope :red, :conditions => {:color => "red"} do
    def turn_blue
      each { |f| f.update_attribute(:color, "blue") }
    end
  end
end

在这种情况下，turn_blue仅适用于红色花朵(因为它不是在 Flower 类中定义，而是在作用域本身中定义).

In this case,turn_blueis only available to red flowers (because it's not defined in the Flower class but in the scope itself).

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