Question

在ActiveRecord中，has_many关系使用外键列来加载关联。所以：

class Person < ActiveRecord::Base
  has_many :messages
end

class Messages < ActiveRecord::Base
  belongs_to :person
end

Person.limit(10).includes(:messages) 
# select * from persons limit 10;
# select messages.* from messages where person_id in (1, 2, 3...)

我有一个案例（我也看到其他人也要求这样做），我不希望Rails自动将外键检查附加到where子句。相反，我可能想要这样的东西：

class Person < ActiveRecord::Base
  has_many :messages, 
           :foreign_key => false, 
           :conditions => proc { ["person_id is null or person_id = ?", self.id] }
end

Person.limit(10).includes(:messages)
# select messages.* from messages where person_id is null or person_id in (1, 2, 3...)

我该怎么做？总而言之，我不希望ActiveRecord自动在WHERE子句中附加外键，我希望能够指定它用于关联的表达式。

我不想这样做：

class Person < ActiveRecord::Base
  def messages
    Message.where("person_id is null or person_id = #{ self.id }")
  end
end

据我所知，这会打破急切的负荷。

我也不想将finder_sql选项用于has_many，因为这样会破坏person.messages.where(:id => 1)或Person.limit(10).includes(:messages => :image)

等内容

Answer 1

这样的东西对我来说适用于Rails 3.2.1：

class Person < ActiveRecord::Base
  has_many :messages, :finder_sql => lambda{ "SELECT * FROM messages WHERE messages.person_id=#{id} OR messages.person_id IS NULL" }
end

# person = Person.includes(:messages).first
# person.messages.loaded?  #=> true

ActiveRecord has_many具有自定义外键sql表达式

1 个答案: