Pitfall: ActiveRecord callbacks: Method call with multiple conditions

Updated . Posted . Visible to the public. Repeats.

In the following example the method update_offices_people_count won't be called when office_id changes, because it gets overwritten by the second line:

after_save :update_offices_people_count, :if => :office_id_changed? # is overwritten …
after_save :update_offices_people_count, :if => :trashed_changed? # … by this line

Instead write:

after_save :update_offices_people_count, :if => :office_people_count_needs_update?

private

def office_people_count_needs_update?
  office_id_changed? || trashed_changed?
end

Or, move the conditions into the callback. This also allows you test the conditions more easily using a unit test:

after_save :update_offices_people_count

private

def update_offices_people_count
  if office_id_changed? || trashed_changed?  
    ...
  end
end

Also see the card on testing conditional validations.

Last edit
Michael Leimstädtner
License
Source code in this card is licensed under the MIT License.

Related cards:

Nested ActiveRecord transaction pitfalls

When working with custom transactions and use ActiveRecord::Rollback you may encounter unexpected behaviour if you try to roll back your changes.

tl;dr

When using nested transactions, ActiveRecord::Rollback might not do what you expect, s...

Inspecting model callback chains

If you need to look at the list of methods that are called upon certain events (like before/after saving etc), do this:

Model._save_callbacks.select {|cb| cb.kind == :before}.map{ |c| c.instance_variable_get :@filter }

Rails 2

...

Rails: When defining scopes with class methods, don't use `self`

Sometimes it is useful to define a named scope by implementing a static method with the scope's name on the scoped class. For instance, when a method should decide which existing scope should be the next link in the scope chain. Take this class fo...

Testing state_machine callbacks without touching the database

You should test the callback methods and its correct invocation in two separate tests. Understand the ActiveRecord note before you move on with this note.

Say this is you...

Save ActiveRecord models without callbacks or validations (in Rails 2 and Rails 3)

Rails 2

You can use

record.send(:update_without_callbacks)

or

record.send(:create_without_callbacks)

This can be used as a lightweight alternative to machinist's make or FactoryGirl's create, when you just need objects...

Testing ActiveRecord callbacks with RSpec

Our preferred way of testing ActiveRecord is to simply create/update/destroy the record and then check if the expected behavior has happened.

We used to bend over backwards to avoid touching the database for this. For this we used a lot of stubbi...

Touch records without running callbacks

ActiveRecord comes with a method touch which sets the updated_at timestamp to the current time. Unfortunately it also runs callbacks (and hence validations) on the receiving record, so i...

JavaScript without jQuery

This is a presentation from 2019-01-21.

Summary

  • We want to move away from jQuery in future projects
  • Motivations are performance, bundle size and general trends for the web platform.
  • The native DOM API is much nicer than it used to be, a...

Cancelling the ActiveRecord callback chain

What Rails version Within before_* Within after_*
Cancel later callbacks Rails 1-4 `re...

Async control flow in JavaScript: Promises, Microtasks, async/await

Slides for Henning's talk on Sep 21st 2017.

Understanding sync vs. async control flow

Talking to synchronous (or "blocking") API

print('script start')
html = get('/foo')
print(html)
print('script end'...
Posted to makandra dev (2013-04-24 14:09)
This website uses short-lived cookies to improve usability.
or learn more