导轨2.3.x - 请问如何ActiveRecord的工作范围？

问题描述

有一个项目我工作的，看起来像下面这样的named_scope：

There's a named_scope in a project I'm working on that looks like the following:

 # default product scope only lists available and non-deleted products
  ::Product.named_scope :active,      lambda { |*args|
    Product.not_deleted.available(args.first).scope(:find)
  }

初​​始named_scope是有道理的。这里的混乱的部分是如何.scope（：找到）的作品。这显然​​是调用另一个名为范围（not_deleted），并应用.scope（：找到）之后。什么/如何做.scope（：找到）在这里工作。

The initial named_scope makes sense. The confusing part here is how .scope(:find) works. This is clearly calling another named scope (not_deleted), and applying .scope(:find) afterwards. What/how does .scope(:find) work here?

推荐答案

一个快速的答案

Product.not_deleted.available(args.first)

是一个命名范围本身，由双方指定范围相结合而形成的。

is a named-scope itself, formed by combining both named scopes.

范围（：找到）得到了一个名为范围的条件（或范围的组合），你可以反过来使用，以创建一个新的命名作用域。

scope(:find) gets the conditions for a named-scope (or combination of scopes), which you can in turn use to create a new named-scope.

因此​​，通过例如：

named_scope :active,      :conditions => 'active  = true'
named_scope :not_deleted, :conditions => 'deleted = false'

那么你就写

named_scope :active_and_not_deleted, :conditions => 'active = true and deleted = false'

或者，你可以写

or, you could write

named_scope :active_and_not_deleted, lambda { self.active.not_deleted.scope(:find) }

这是相同的。我希望讲清楚。

which is identical. I hope that makes it clear.

请注意，这已经变得越来越简单（清洁剂）的轨道3，你只写

Note that this has become simpler (cleaner) in rails 3, you would just write

scope :active_and_not_deleted, active.not_deleted

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