使用ActiveRecord自行加入桌面

Question

我有一个ActiveRecord调用Name,其中包含各种名称Languages.

class Name < ActiveRecord::Base
  belongs_to :language

class Language < ActiveRecord::Base
  has_many :names

用一种语言查找名称很容易:

Language.find(1).names.find(whatever)

但我需要找到匹配的对,其中语言1和语言2具有相同的名称.在SQL中,这需要一个简单的自联接:

SELECT n1.id,n2.id FROM names AS n1, names AS n2
  WHERE n1.language_id=1 AND n2.language_id=2
    AND n1.normalized=n2.normalized AND n1.id != n2.id;

如何使用ActiveRecord执行此类查询？请注意,我需要找到一对名称(=匹配的两侧),而不仅仅是语言1中恰好与某些内容匹配的名称列表.

对于奖励积分,替换n1.normalized=n2.normalized为n1.normalized LIKE n2.normalized,因为该字段可能包含SQL通配符.

我也对以不同方式建模数据的想法持开放态度,但如果可以的话,我宁愿避免为每种语言使用单独的表.

Answer 1

试试这个:

ids = [1,2]
Name.all(:select    => "names.id, n2.id AS id2",
         :joins     => "JOIN names AS n2 
                              ON n2.normalized = names.normalized AND 
                                 n2.language_id != names.language_id AND
                                 n2.language_id IN (%s)" % ids.join(','),
         :conditions => ["names.language_id IN (?)", ids]
).each do |name|
  p "id1 : #{name.id}"
  p "id2 : #{name.id2}"
end

PS:确保清理传递给连接条件的参数.