postgresql – postgres数据库错误强制重启事务

我正在将一个mysql应用程序迁移到postgres …我曾经在mysql-land中遵循这样的模式将连接表记录添加到DB：

class EventsSeries < ActiveRecord::Base
  #  UNIQUE KEY `index_events_series_on_event_id_and_series_id` (`event_id`,`series_id`)
  belongs_to :event
  belongs_to :series
end

class Series < ActiveRecord::Base

  has_many :events_series
  before_validation :add_new_event

private

  def add_new_event
    # boils down to something like this
    EventSeries.new.tap do |es|
      es.event_id = 1
      es.series_id = 1
      begin
        es.save!
      rescue ActiveRecord::RecordNotUnique
        # Great it exists
        # this isn't really a problem
        # please move on
      end
    end
  end
end

像这样调用：

Series.first.save 
# should not blow up on duplicate join record,cause i don't care

然而,postgres在这上面爆发了.这里有一个很好的解释：

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

…在“异常处理和回滚”部分(请参阅警告)

基本上#save启动一个事务,并且重复记录插入导致数据库异常,这使#saving的事务无效,这是悲伤的.

有没有更好的模式可以用于postgres-land？

谢谢！

编辑：

我坚信将这个逻辑保留在Series的保存事务中是有意义的……模式看起来像这样：

s = Series.new
s.new_event_id = 123 # this is just an attr_accessor
s.save # callbacks on Series know how to add the new event.

…它使我的控制器超小.