Rails：:inverse_of和关联扩展

Question

我有以下设置

class Player < ActiveRecord::Base
  has_many :cards, :inverse_of => :player do
    def in_hand
      find_all_by_location('hand')
    end
  end
end

class Card < ActiveRecord::Base
  belongs_to :player, :inverse_of => :cards
end

这意味着以下工作：

p = Player.find(:first)
c = p.cards[0]
p.score # => 2
c.player.score # => 2
p.score += 1
c.player.score # => 3
c.player.score += 2
p.score # => 5

但以下代码的行为与此不同：

p = Player.find(:first)
c = p.cards.in_hand[0]
p.score # => 2
c.player.score # => 2
p.score += 1
c.player.score # => 2
c.player.score += 2
p.score # => 3

d = p.cards.in_hand[1]
d.player.score # => 2

如何使:inverse_of关系扩展到扩展方法？(这只是一个bug吗？)

Answer 1

它不起作用，因为"in_hand“方法有一个返回到数据库的查询。

由于inverse_of选项，工作代码知道如何使用内存中已经存在的对象。

http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

Answer 2

如果(和我一样)你愿意放弃Arel授予的SQL优化，而只使用Ruby，我已经找到了一个解决办法。

class Player < ActiveRecord::Base
  has_many :cards, :inverse_of => :player do
    def in_hand
      select {|c| c.location == 'hand'}
    end
  end
end

class Card < ActiveRecord::Base
  belongs_to :player, :inverse_of => :cards
end

通过编写扩展来过滤Ruby语言中关联的全部结果，而不是缩小SQL查询的范围，扩展返回的结果在:inverse_of中表现正确。

p = Player.find(:first)
c = p.cards[0]
p.score # => 2
c.player.score # => 2
p.score += 1
c.player.score # => 3
c.player.score += 2
p.score # => 5

d = p.cards.in_hand[0]
d.player.score # => 5
d.player.score += 3
c.player.score # => 8