Mongoid 7.x runs callback even when no changes for update?

[sachiotomita]

7.0.0.beta
The release contains a large refactor of the way associations are defined between models
https://github.com/mongodb/mongoid/releases/tag/v7.0.0.beta

Hello,
I'm upgrading Mongoid 6 to 7 (on existing Rails app). due to rails upgrade..

As I searched, Mongoid 7 has breaking change on association(refactoring).

When upgrade to 7.x
my rails app is calling update callbacks(before_update/after_update, etc.) every time related model's save/create,
even when no changes to update,
if the association is autosave: true

it can cause many unexpected behaviors on callbacks process.

why? and how to avoid this many unwanted callbacks?

Image should be immutable, but update callback is called. when create().

backtrace (from update on controller, to callback)

--> #0  Image.before_update at /dev/my-org/my-rails-app/app/models/image.rb:128
    #1  block in ActiveSupport::Callbacks::CallTemplate.block in make_lambda at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/activesupport-6.0.5/lib/active_support/callbacks.rb:428
    #2  block (2 levels) in #<Class:ActiveSupport::Callbacks::Filters::Before>.block (2 levels) in halting(callback_sequence#ActiveSupport::Callbacks::CallbackSequence, user_callback#Proc, halted_lambda#Proc, filter#Symbol) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/activesupport-6.0.5/lib/active_support/callbacks.rb:200
    #3  block (2 levels) in ActiveSupport::Callbacks::CallbackChain.block (2 levels) in default_terminator at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/activesupport-6.0.5/lib/active_support/callbacks.rb:605
    ͱ-- #4  Kernel.catch(*args) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/activesupport-6.0.5/lib/active_support/callbacks.rb:604
    #5  block in ActiveSupport::Callbacks::CallbackChain.block in default_terminator at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/activesupport-6.0.5/lib/active_support/callbacks.rb:604
    #6  block in #<Class:ActiveSupport::Callbacks::Filters::Before>.block in halting(callback_sequence#ActiveSupport::Callbacks::CallbackSequence, user_callback#Proc, halted_lambda#Proc, filter#Symbol) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/activesupport-6.0.5/lib/active_support/callbacks.rb:201
    #7  block in ActiveSupport::Callbacks::CallbackSequence.block in invoke_before(arg#ActiveSupport::Callbacks::Filters::Environment) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/activesupport-6.0.5/lib/active_support/callbacks.rb:513
    ͱ-- #8  Array.each at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/activesupport-6.0.5/lib/active_support/callbacks.rb:513
    #9  ActiveSupport::Callbacks::CallbackSequence.invoke_before(arg#ActiveSupport::Callbacks::Filters::Environment) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/activesupport-6.0.5/lib/active_support/callbacks.rb:513
    #10 ActiveSupport::Callbacks.run_callbacks(kind#Symbol) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/activesupport-6.0.5/lib/active_support/callbacks.rb:134
    #11 Mongoid::Interceptable.run_callbacks(kind#Symbol, *args#Array, &block#Proc) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/interceptable.rb:135
    #12 block in Mongoid::Persistable::Updatable.block in prepare_update(options#Hash) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/persistable/updatable.rb:113
    #13 ActiveSupport::Callbacks.run_callbacks(kind#Symbol) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/activesupport-6.0.5/lib/active_support/callbacks.rb:135
    #14 Mongoid::Interceptable.run_callbacks(kind#Symbol, *args#Array, &block#Proc) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/interceptable.rb:135
    #15 Mongoid::Persistable::Updatable.prepare_update(options#Hash) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/persistable/updatable.rb:112
    #16 Mongoid::Persistable::Updatable.update_document(options#Hash) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/persistable/updatable.rb:134
    #17 Mongoid::Persistable::Savable.save(options#Hash) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/persistable/savable.rb:27
    #18 block in Mongoid::Persistable::Creatable::ClassMethods.block in create(attributes#Hash, &block#NilClass) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/persistable/creatable.rb:153
    #19 Mongoid::Threaded::Lifecycle::ClassMethods._creating at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/threaded/lifecycle.rb:163
    #20 Mongoid::Persistable::Creatable::ClassMethods.create(attributes#Hash, &block#NilClass) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/persistable/creatable.rb:148
    #21 Asset.image=(file#String) at /dev/my-org/my-rails-app/app/models/asset.rb:90
    #22 Mongoid::Attributes::Processing.process_attribute(name#String, value#String) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/attributes/processing.rb:102
    #23 block in Mongoid::Attributes::Processing.block in process_attributes(attrs#ActiveSupport::HashWithIndifferentAccess) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/attributes/processing.rb:27
    ͱ-- #24 Hash.each_pair at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/attributes/processing.rb:25
    #25 Mongoid::Attributes::Processing.process_attributes(attrs#ActiveSupport::HashWithIndifferentAccess) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/attributes/processing.rb:25
    #26 block in Mongoid::Attributes.block in assign_attributes(attrs#ActionController::Parameters) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/attributes.rb:208
    #27 Mongoid::Threaded::Lifecycle._assigning at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/threaded/lifecycle.rb:33
    #28 Mongoid::Attributes.assign_attributes(attrs#ActionController::Parameters) at /dev/my-org/my-rails-app/vendor/bundle/ruby/2.7.0/gems/mongoid-7.3.4/lib/mongoid/attributes.rb:207
    #29 Api::AssetsController.update at /dev/my-org/my-rails-app/app/controllers/api/assets_controller.rb:70

https://github.com/mongodb/mongoid/blob/master/lib/mongoid/persistable/updatable.rb#L133

https://github.com/mongodb/mongoid/blob/master/lib/mongoid/interceptable.rb#L9

[p-mongo]

When you enable autosaving, you are asking for the child models to be taken through the save process. There may not be any changes written to the database but Mongoid still has to go through all of the models and attempt to save them.

[p-mongo]

AR works the same way:

class Band < ApplicationRecord
  before_update do
    puts 'before update'
  end

  after_update do
    puts 'after update'
  end
end



serene2% rails c
Loading development environment (Rails 6.1.5)
irb(main):001:0> b=Band.create!
   (0.4ms)  SELECT sqlite_version(*)
  TRANSACTION (0.0ms)  begin transaction
  Band Create (0.2ms)  INSERT INTO "bands" ("created_at", "updated_at") VALUES (?, ?)  [["created_at", "2022-07-28 16:36:22.901826"], ["updated_at", "2022-07-28 16:36:22.901826"]]
  TRANSACTION (2.8ms)  commit transaction
=> 
#<Band:0x00007fe68ae551c8
...
irb(main):002:0> b.save!
before update
after update
=> true
irb(main):003:0>