ruby-on-rails – SELECT DISTINCT,ORDER BY表达式的PG错误尝试

ActiveRecord::StatementInvalid (PG::Error: ERROR:  for SELECT DISTINCT,ORDER BY expressions must appear in select list

这是我的traveldeal控制器：

def show
    @traveldeal = @commentable = Traveldeal.find(params[:id])
    @comments = Comment.all
    @title = @traveldeal.title
    @eventdeals = Eventdeal.tagged_with(@traveldeal.location_tag_list,:any => true,:order => 'RANDOM()',:limit => 3)
  end

traveldeal / show.html

<% unless @eventdeals.blank? %>

  <h1>Events in the area:</h1>

  <% @eventdeals.each do |eventdeal| %>
    <%= link_to eventdeal do %>
      <!-- content -->
    <% end %>
  <% end %>

<% end %>

Heroku日志

SELECT DISTINCT eventdeals.* FROM “eventdeals” JOIN的Tagging event_taggings_e9f0e2e ON event_taggings_e9f0e2e.taggable_id = eventdeals.id AND event_taggings_e9f0e2e.taggable_type = ‘Eventdeal’ WHERE(event_taggings_e9f0e2e.tag_id = 1 OR event_taggings_e9f0e2e.tag_id = 3 OR event_taggings_e9f0e2e.tag_id = 4 OR event_taggings_e9f0e2e. tag_id = 5)ORDER BY RANDOM())：

这段代码正在工作,所以我只显示了3个随机事件,它们与一个traveldeal匹配的位置(通过act-as-taggable-on).

然而,在我添加了一个关系(与eventdeals而不是traveldeals相关)后,我开始得到pg错误.

以下是添加的关系：

trip.rb

class Trip < ActiveRecord::Base
  has_many :eventdealtrips,:dependent => :destroy
  has_many :eventdeals,:through => :eventdealtrips
end

eventdeal.rb

class Eventdeal < ActiveRecord::Base
  has_many :eventdealtrips
  has_many :trips,:through => :eventdealtrips,:dependent => :destroy
end

eventdealtrip.rb

class Eventdealtrip < ActiveRecord::Base
  belongs_to :eventdeal
  belongs_to :trip
end

任何建议,我如何仍然可以得到一个随机数组的3事件？

谢谢.