Eager loading with relations causes touch option not to work

Question

When using includes to eager load an active record, the updated_at does not get updated.

Simplified code:

class MyModel < ApplicationRecord
  has_many :comments,
           foreign_key: 'my_model_id',
           dependent: :destroy,
           inverse_of: :my_model

end

class Comments < ApplicationRecord
  belongs_to :my_model, foreign_key: :my_model_id,
                        inverse_of: :comments,
                        touch: true
end

model = MyModel.includes(comments: :user).find_by!(my_id: 111)
params = {"comments_attributes"=>{"0"=>{"id"=>"2", "name"=>"aaa"}}
model.update(params)
# model.updated_at DOES NOT get updated.

model = MyModel.find_by!(my_id: 111)
params = {"comments_attributes"=>{"0"=>{"id"=>"2", "name"=>"aaa"}}
model.update(params)
# model.updated_at DOES get updated.

Why would the touch option not work when eager loading?

Answer 1

In short, we should avoid includes when we need the touch option to work correctly on the parent. See here for a more detailed answer.