activerecord - Why does updating a model trigger rails to load other models?

Question

I've got a weird behavior on my project. If I update/save a record on my ::Product model, rails always load up other models relates to it.

this:

p = Product.first
p.update(name: 'whatever')

will output this:

 (1.2ms)  BEGIN
  Product::Brand Load (2.6ms)  SELECT  `product_brands`.* FROM `product_brands` WHERE `product_brands`.`id` = 24 LIMIT 1
  Product::Condition Load (5.4ms)  SELECT  `product_conditions`.* FROM `product_conditions` WHERE `product_conditions`.`id` = 3 LIMIT 1
  Product::Category Load (1.3ms)  SELECT  `product_categories`.* FROM `product_categories` WHERE `product_categories`.`id` = 2 LIMIT 1
  Product Update (4.0ms)  UPDATE `products` SET `updated_at` = '2021-01-28 21:10:16', `name` = 'whatever' WHERE `products`.`id` = 1
   (0.5ms)  COMMIT

product belongs to :brand, :condition, and :category, but it also belongs to other models as well, but only these three models got triggered.

Any idea why this happened?

EDIT I didn't set any custom validation in the Product class. Nor does scope or default_scope.

EDIT 2 I just realised something. It doesn't only happen in my Product model. But ALL models that have belongs_to :something relationship will trigger the same queries, unless I add optional: true. Is it an intended behavior for Rails? Can I prevent this without adding optional: true to the belongs_to relation?

question from:https://stackoverflow.com/questions/65938886/why-does-updating-a-model-trigger-rails-to-load-other-models

Answer 1

Can you post the code from the Product model? Validations, scopes, callbacks, basically everything except methods. Most probably you have something that causes the eager loading there. The most obvious would be:

has_many :brands, :include => true

include :brands

default_scope includes(:brands)

Also as Sergio pointed out, many callbacks and validations can load these related models to perform some actions.