使用＆QUOT;自＆QUOT;在报关协会（：的has_many，：HAS_ONE） [英] using "self" in association declaration (:has_many, :has_one)

问题描述

我需要参考模型的自我在：的has_many声明。

I need to reference a model's self in a :has_many declaration.

我有一类我们称之为富。富：的has_many吧。美孚有一个名为随机化布尔属性，决定在该酒吧的顺序：的has_many关系。如果随机化是真实的，那么他们是通过有序的RAND（）或RANDOM（），这取决于数据库。如果不是这样，它们被标识排序。我有，因为我使用立即加载作出这一声明的关联。我充分意识到，我可以定义foo的方法，返回我想要什么，但我需要的一切加载一次或者400-500查询运行单独=坏。

I have a class we will call Foo. Foo :has_many Bar. Foo has a boolean attribute called randomize that determines the order of the the Bars in the :has_many relationship. If randomize is true, then they are ordered by "RAND()" or "RANDOM()" depending on the DB. If not, they are ordered by id. I HAVE to make this declaration on the association because I am using eager loading. I am well-aware that I can define a method in Foo that returns what I want, but I need to have everything loaded at once or else 400-500 queries are run individually = bad.

class CreateFoo < ActiveRecord::Migration
  def self.up
    create_table :foos do |t|
      t.string :name
      t.boolean :randomize, :default => false
    end
  end
end

＆NBSP;

 

class CreateBar < ActiveRecord::Migration
  def self.up
    create_table :bars do |t|
      t.string :name
      t.references :foo
    end
  end
end

＆NBSP;

 

class Bar < ActiveRecord::Base
  belongs_to :foo
end

＆NBSP;

 

class Foo < ActiveRecord::Base
  # this is the line that doesn't work
  has_many :bars, :order => self.randomize ? 'RAND()' : 'id'
end

我如何访问的自的性质在的has_many声明？

How do I access properties of self in the has_many declaration?

的事情，失败：

1. 创建富的方法，它返回正确的字符串
2. 创建一个lambda函数
3. 哭

这可能吗？

这个问题似乎是，在自我：的has_many的类型是富不：

The problem seems to be that the "self" in :has_many ISN'T of type Foo:

undefined method `randomize' for #<Class:0x1076fbf78>

是我得到的错误之一。需要注意的是它的一般类，而不是Foo对象？为什么？

is one of the errors I get. Note that its a general Class, not a Foo Object... Why??

推荐答案

原来瑞安贝茨谈到一个话题这类似于的此处在Railscast。您需要定义范围的方法之后...

Turns out Ryan Bates has touched on a simliar topic here in a Railscast. You need to define the scope AFTER the method...

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