Question

我试图通过：through和：source选项使用两个相似的多态关联来进行SQL搜索。我看到的是，rails正在为第一个“has_many：reservation_trip_itinerary_entries ......”遗漏一个表名别名。

奖金问题：是否可以创建一个新的关联或别名，它将返回一个关联，但如果一个为空，则还原为备份？也许这值得另一个问题？

这是行程条目（通过TripType和分支ReservationTrip预订的子项，每个包含一个单独的列表）：

class ItineraryEntry < ActiveRecord::Base

    default_scope order('position ASC')

    attr_accessible :title, :code, :datetime, :position, :itinerary_type, :itinerary_id, :action_type, :action_id
    belongs_to :itinerary, polymorphic: true
    belongs_to :action, polymorphic: true

这是预订（许多ItineraryEntries的父级）：

class Reservation < ActiveRecord::Base
    has_many :reservation_trips, :order => :departure_date, :dependent => :destroy
    has_many :trip_types, :through => :reservation_trips  # contact booking report                                                                                            
    has_many :reservation_trip_itinerary_entries, :through => :reservation_trips, :source => :itinerary_entries
    has_many :trip_type_itinerary_entries, :through => :trip_types, :source => :itinerary_entries

    # excluded irrelevant methods

    def search

        # many other search params excluded, all populating 'includes' and
        # 'warez' in the same way

        if params.key?(:itinerary_entry) and not params[:itinerary_entry].empty?
            includes.push(:reservation_trip_itinerary_entries)
            includes.push(:trip_type_itinerary_entries)
            warez.push("(                                                                                                                                                         
      (reservation_trip_itinerary_entries.action_type = '#{params[:itinerary_entry][:action_type]}' AND                                                                 
       reservation_trip_itinerary_entries.action_id = #{params[:itinerary_entry][:action_id]})                                                                          
      OR                                                                                                                                                                
      (trip_type_itinerary_entries.action_type = '#{params[:itinerary_entry][:action_type]}' AND                                                                        
       trip_type_itinerary_entries.action_id = #{params[:itinerary_entry][:action_id]})                                                                                 
  )")
        end
        Reservation.includes(includes).where(warez.join(' AND ')).order('reservations.created_at DESC').limit(params[:limit])
    end

这是它正在生成的sql，带有错误。请注意第一个“itinerary_entries”列表如何在第二个列表中没有别名（“trip_type_itinerary_entries_reservations”）：

SELECT DISTINCT "reservations".id,
                reservations.created_at AS alias_0
FROM "reservations"
LEFT OUTER JOIN "reservation_trips" ON "reservation_trips"."reservation_id" = "reservations"."id"
LEFT OUTER JOIN "itinerary_entries" ON "itinerary_entries"."itinerary_id" = "reservation_trips"."id"
AND "itinerary_entries"."itinerary_type" = 'ReservationTrip'
LEFT OUTER JOIN "reservation_trips" "reservation_trips_reservations_join" ON "reservation_trips_reservations_join"."reservation_id" = "reservations"."id"
LEFT OUTER JOIN "trip_types" ON "trip_types"."id" = "reservation_trips_reservations_join"."trip_type_id"
LEFT OUTER JOIN "itinerary_entries" "trip_type_itinerary_entries_reservations" ON "trip_type_itinerary_entries_reservations"."itinerary_id" = "trip_types"."id"
AND "trip_type_itinerary_entries_reservations"."itinerary_type" = 'TripType'
WHERE (( (reservation_trip_itinerary_entries.action_type = 'Activity'
          AND reservation_trip_itinerary_entries.action_id = 3)
        OR (trip_type_itinerary_entries.action_type = 'Activity'
            AND trip_type_itinerary_entries.action_id = 3) ))
ORDER BY reservations.created_at DESC LIMIT 100

这是SQL错误：

PG::Error: ERROR:  missing FROM-clause entry for table "reservation_trip_itinerary_entries"
LINE 2:           (reservation_trip_itinerary_entries.action_type = ...
                   ^

思考？谢谢！

Answer 1

玩完这个之后，我发现ActiveRecord在这里有一个细微差别。它不会为第一个关联指定别名（在原始问题中命名为“itinerary_entries”），但会为所有后续关联指定别名。

所以我通过黑客攻击我的WHERE子句得到了我的查询，如下所示：

if params.key?(:itinerary_entry) and not params[:itinerary_entry].empty?
  includes.push(trip_types: [:itinerary_entries], reservation_trips: [:itinerary_entries])
  warez.push("                                                                                                          
      (itinerary_entries.action_type = '#{params[:itinerary_entry][:action_type]}' AND                                  
       itinerary_entries.action_id = #{params[:itinerary_entry][:action_id]}) OR                                        
      (itinerary_entries_trip_types.action_type = '#{params[:itinerary_entry][:action_type]}' AND                       
       itinerary_entries_trip_types.action_id = #{params[:itinerary_entry][:action_id]})                                
  ")
end

哪个产生了这个查询

SELECT DISTINCT "reservations".id, 
                reservations.created_at AS alias_0 
FROM   "reservations" 
       LEFT OUTER JOIN "reservation_trips" 
                    ON "reservation_trips"."reservation_id" = 
                       "reservations"."id" 
       LEFT OUTER JOIN "itinerary_entries" 
                    ON "itinerary_entries"."itinerary_id" = 
                       "reservation_trips"."id" 
                       AND "itinerary_entries"."itinerary_type" = 
                           'ReservationTrip' 
       LEFT OUTER JOIN "reservation_trips" "reservation_trips_reservations_join" 
                    ON "reservation_trips_reservations_join"."reservation_id" = 
                       "reservations"."id" 
       LEFT OUTER JOIN "trip_types" 
                    ON "trip_types"."id" = 
       "reservation_trips_reservations_join"."trip_type_id" 
       LEFT OUTER JOIN "itinerary_entries" "itinerary_entries_trip_types" 
                    ON "itinerary_entries_trip_types"."itinerary_id" = 
                       "trip_types"."id" 
                       AND "itinerary_entries_trip_types"."itinerary_type" = 
                           'TripType' 
WHERE  ( ( itinerary_entries.action_type = 'Activity' 
           AND itinerary_entries.action_id = 3 ) 
          OR ( itinerary_entries_trip_types.action_type = 'Activity' 
               AND itinerary_entries_trip_types.action_id = 3 ) ) 
ORDER  BY reservations.created_at DESC 
LIMIT  100

Rails：多态关联不包括连接中的正确表别名？

1 个答案: