has_many :through eager loading only loading one record

rubyonrails-talk
1

Hello,

I've been using Rails for years, including has_many :through and eager loading, but this one has me stumped.

The problem is that Active Record is only eager-loading the first of many records. Here are the models (note set_table_name for a legacy schema):

class Tag < ActiveRecord::Base   set_table_name 'tag' end

class DishTag < Tag   has_many :dish_taggings, :foreign_key => 'tag_id'   has_many :dishes, :through => :dish_taggings end

class DishTagging < ActiveRecord::Base   set_table_name 'dish_tag'   belongs_to :dish   belongs_to :dish_tag, :foreign_key => 'tag_id' end

class Dish < ActiveRecord::Base   set_table_name 'dish'   has_many :dish_taggings, :foreign_key => 'tag_id'   has_many :tags, :through => :dish_taggings, :source => :dish_tag end

In the controller, I eager-load like this:

@tags = DishTag.find(:all, :include => {:dish_taggings => :dish})

Here are the resulting queries (with traces thanks to the query_trace plugin):

DishTag Columns (1.2ms) SHOW FIELDS FROM `tag`   DishTag Load (0.9ms) SELECT * FROM `tag` WHERE ( (`tag`.`type` = 'DishTag' ) )     app/controllers/tags_controller.rb:5:in `index'   DishTagging Load (6.9ms) SELECT `dish_tag`.* FROM `dish_tag` WHERE (`dish_tag`.tag_id IN (58,60,61,62,63,79,81,82,83,90,91,93,94,96,97,99,102,104,106,109,110,114,120,121,122,123,124,125,126,127,131,132,133,135,136,137,138,139,141,143,144,145,146,147,149,150,153,154,157,158,161,166,178,181,184,199,229,232,235,238,259,262,277,283,298,301,304,307,310,313,322,331,334,337,340,343,346,352,355,358,361,364,370,373,376,379,391,394,400,403,406,409,412,415,418,436,439,442,445,448,451,454,457,481,484,532,535,547,550,553,556,559,562,568,580,706,721,724,730,733,736,739,742,745,748,751,754,757,760,763,766,769,778,781,784,787,790,793,796,799,802,805,808,811,814,817,820,823,826,829,832,835,838,841,844,847,850,853,856,859,862,865,868,871,874,877,880,883,886,889,892,895,898,901,904,907,910,913,916,919,922,925,928,934,937,940,943,946,949,952,955,958,961,964,967,970,973,979,982,985,988,991,994,1003,1006,1009,1012,1015,1018,1021,1024,1027,1030,1033,1036,1039,1042,1045,1048,1051,1054,1057,1060,1063,1066,1069,1072,1075,1078,1081,1084,1087))     app/controllers/tags_controller.rb:5:in `index'   DishTagging Columns (1.2ms) SHOW FIELDS FROM `dish_tag`   Dish Columns (2.0ms) SHOW FIELDS FROM `dish`   Dish Load (0.4ms) SELECT * FROM `dish` WHERE (`dish`.`id` = 209)     app/controllers/tags_controller.rb:5:in `index'

Notice that in DishTagging Load, the first foreign key in the list is 58. As it turns out, there is only one DishTagging witth tag_id 58, and its dish_id is 209. Now look at Dish Load: it's loading dish 209 and nothing else.

So, this leads me to believe that only the first related record is being eager-loaded. Sure enough, when I iterate, Active Record loads each dish individually except for dish 209.

Any thoughts on why this is happening? I've never seen this problem before. I'm guessing it has something to do with all the stuff I've had to override in the model configs (e.g. table names and foreign keys.) But I'm not getting any exceptions.

2

Dumb question: Are their dish_tags with tag_id 60,61,62 etc. What is their dish_id ?

Fred

3

> Notice that in DishTagging Load, the first foreign key in the list is > 58. As it turns out, there is only one DishTagging witth tag_id 58, > and its dish_id is 209. Now look at Dish Load: it's loading dish 209 > and nothing else.

Dumb question: Are their dish_tags with tag_id 60,61,62 etc. What is their dish_id ?

Another thought - you seem to have some sort of STI thing going on (DishTag < Tag). Does the type column on the tags column contain appropriate values?

Fred