Question

I have the following model structure:

class Group < ActiveRecord::Base
  has_many    :group_products, :dependent => :destroy
  has_many    :products, :through => :group_products
end

class Product < ActiveRecord::Base
  has_many  :group_products, :dependent => :destroy
  has_many  :groups, :through => :group_products
end

class GroupProduct < ActiveRecord::Base
  belongs_to :group
  belongs_to :product
end

I wanted to minimize my database queries so I decided to use includes.In the console I tried something like,

groups = Group.includes(:products)

my development logs show the following calls,

Group Load (403.0ms)  SELECT `groups`.* FROM `groups`
GroupProduct Load (60.0ms)  SELECT `group_products`.* FROM `group_products` WHERE (`group_products`.group_id IN (1,3,14,15,16,18,19,20,21,22,23,24,25,26,27,28,29,30,33,42,49,51))
Product Load (22.0ms)  SELECT `products`.* FROM `products` WHERE (`products`.`id` IN (382,304,353,12,63,103,104,105,262,377,263,264,265,283,284,285,286,287,302,306,307,308,328,335,336,337,340,355,59,60,61,247,309,311,66,30,274,294,324,350,140,176,177,178,64,240,327,332,338,380,383,252,254,255,256,257,325,326))
Product Load (10.0ms)  SELECT `products`.* FROM `products` WHERE (`products`.`id` = 377) LIMIT 1

I could analyze the initial three calls were necessary but don’t get the reason why the last database call is made,

 Product Load (10.0ms)  SELECT `products`.* FROM `products` WHERE (`products`.`id` = 377) LIMIT 1

Any idea why this is happening?
Thanks in advance. 🙂

Answer 1

I don’t think that fourth query is coming from this line of code (or the collection created by it). Even if you did something like groups.products.find(product_id) somewhere later, you would see a much more complex query, with the inner joins on the join table. It looks like there must be a separate Product.find(product_id) or something similar somewhere in your code.