提取到组合类中

如果一个模型中有一些关联字段，例如一个用户有一个address_city和一个address_street，你可以把它们提取到组合类中去。

 

丑陋的

 

# == Schema Information
#  address_city        :string(255)
#  address_street      :string(255)
class Customer < ActiveRecord::Base
  def address_close_to?(other_customer)
    address_city == other_cutomer.address_city
  end

  def address_equal(other_customer)
    address_street == other_customer.address_street &&
      address_city == other_customer.address_city
  end
end

 

可以看到Customer有两个属性address_city和address_street，但是应该是Address的属性，如果你不想创建一个addresses的数据库表的话，你只要创建一个组合类Address。

 

重构

 

class Customer < ActiveRecord::Base
  composed_of :address, :mapping => [ %w(address_street street), %w(address_city city)]
end

class Address
  attr_reader :street, :city

  def initialize(street, city)
    @street, @city = street, city
  end

  def close_to?(other_address)
    city == other_address.city
  end

  def ==(other_address)
    city == other_address.city && street == other_address.street
  end
end

 

Rails提供了一个帮助方法composed_of来方便的提取一个组合类，这里我们为Customer添加了一个叫Address的组合类，在Address模型中我们使用了street和city属性，并且和Customer模型中的address_street和address_city对应。