Use synvert to upgrade Dirty API to ActiveRecord 5.1

TL;DR you can run synvert-ruby -r rails/convert_active_record_dirty_5_0_to_5_1 <project_path> to upgrade active_record dirty api.

Rails 5.1 introduced a new ActiveRecord dirty API, we need to use some longer but less ambiguity methods.

	before callbacks	after callbacks
<attribute>_changed?	will_save_change_to_<attribute>?	saved_change_to_<attribute>?
<attribute>_change	<attribute>_change_to_be_saved	saved_change_to_<attribute>
<attribute>_was	<attribute>_in_database	<attribute>_before_last_save
changes	changes_to_save	saved_changes
changed?	has_changes_to_save?	saved_changes?
changed	changed_attribute_names_to_save	saved_changes.keys
changed_attributes	attributes_in_database	saved_changes.transform_values(&:first)

As you can see, the dirty apis start to use different method names for before and after callbacks, it’s hard to use simple text find and replace, so I use synvert-ruby to make the conversions.

Use the synvert snippet

The snippet name is rails/convert_active_record_dirty_5_0_to_5_1, so you can run the following command to automatically convert the dirty api.

$ synvert-ruby -r rails/convert_active_record_dirty_5_0_to_5_1 <project_path>

Here are a small part of the long git diff.

   before_save do
-    edit if title_changed? || content_changed?
+    edit if will_save_change_to_title? || will_save_change_to_content?
   end

   after_save do
-    self.just_ended = (ended? && ended_at_changed?)
+    self.just_ended = (ended? && saved_change_to_ended_at?)
   end

-  after_update :send_email, :if => :email_changed?
+  after_update :send_email, :if => :saved_change_to_email?

-  tag_changes = node.changes['tag']
+  tag_changes = node.saved_changes['tag']

Write the synvert snippet

So how did I write the snippet?

First, I defined the files to match, rails model and observer files.

within_files Synvert::RAILS_MODEL_FILES + Synvert::RAILS_OBSERVER_FILES do
  ...
end

1. let’s try to convert <attribute>_changed? to saved_change_to_<attribute> for after_save callback in if/unless parameter.

# after_save :invalidate_cache, if: -> { title_changed? || summary_chagned? }
with_node type: 'send', receiver: nil, message: 'after_save' do
  with_node type: 'hash' do
    with_node type: 'sym', to_value: /(\w+)_changed\?$/ do
      if node.to_value =~ /(\w+)_changed\?$/ # match regexp again to get the last match
        replace_with ":saved_change_to_#{Regexp.last_match(1)}?"
      end
    end
  end
end

It uses with_node to match the after_save callback first, then hash parameters, then sym value to match <attribute>_changed?, and replace the symbol with :saved_change_to_<attribute>

2. match all after callbacks

after_callback_names = %i[after_create after_update after_save after_commit after_create_commit after_update_commit after_save_commit]
with_node type: 'send', receiver: nil, message: { in: after_callback_names } do
end

3. do the conversion in after_save block.

# before_save do
#   if status_chagned?
#   end
# end
with_node type: 'block',
          caller: { type: 'send', receiver: nil,
          message: { in: after_callback_names } } do
  with_node type: 'send', message: /(\w+)_changed\?$/ do
    if node.to_value =~ /(\w+)_changed\?$/ # match regexp again to get the last match
      replace_with ":saved_change_to_#{Regexp.last_match(1)}?"
    end
  end
end

4. do the conversion in after_save method.

# def after_save
#   if status_chagned?
#   end
# end
with_node type: 'def', name: { in: after_callback_names } do
  with_node type: 'send', message: /(\w+)_changed\?$/ do
    if node.to_value =~ /(\w+)_changed\?$/ # match regexp again to get the last match
      replace_with ":saved_change_to_#{Regexp.last_match(1)}?"
    end
  end
end

5. do the conversion in after_save custom callback method.

# after_save :invalidate_cache
# def invalidate_cache
#   if status_chagned?
#   end
# end
custom_callback_names = []

with_node type: 'send',
          receiver: nil,
          message: { in: after_callback_names },
          arguments: { size: { gt: 0 }, first: { type: 'sym' }} do
  custom_callback_names << node.arguments[0].to_value
end

with_node type: 'def', name: { in: custom_callback_names } do
  with_node type: 'send', message: /(\w+)_changed\?$/ do
  if node.to_value =~ /(\w+)_changed\?$/ # match regexp again to get the last match
    replace_with ":saved_change_to_#{Regexp.last_match(1)}?"
  end
end

It finds all custom callback methods first, then find <attribute>_changed? in those custom methods.

6. match all after callbacks api changes

after_callback_changes = {
  /(\w+)_changed\?$/ => 'saved_change_to_?',
  /(\w+)_change$/ => 'saved_change_to_',
  /(\w+)_was$/ => '_before_last_save',
  'changes' => 'saved_changes',
  'changed?' => 'saved_changes?',
  'changed' => 'saved_changes.keys',
  'changed_attributes' => 'saved_changes.transform_values(&:first)'
}

after_callback_changes.each do |before_name, after_name|
  with_node type: 'send', message: before_name do
    if before_name.is_a?(Regexp)
      if node.message.to_s =~ before_name # match regexp again to get the last match
        replace :message, with: after_name.sub('', Regexp.last_match(1))
      end
    else
      replace :message, with: after_name
    end
  end
end

7. what about before callbacks? That’s easy, just abstract the above conversions and reuse for before callbacks

before_callback_changes = {
  /(\w+)_changed\?$/ => 'will_save_change_to_?',
  /(\w+)_change$/ => '_change_to_be_saved',
  /(\w+)_was$/ => '_in_database',
  'changes' => 'changes_to_save',
  'changed?' => 'has_changes_to_save?',
  'changed' => 'changed_attribute_names_to_save',
  'changed_attributes' => 'attributes_in_database'
}

before_callback_names = %i[before_create before_update before_save]

helper_method :find_callbacks_and_convert do |callback_names, callback_changes|
  ...
end

within_files Synvert::RAILS_MODEL_FILES + Synvert::RAILS_OBSERVER_FILES do
  find_callbacks_and_convert(before_callback_names, before_callback_changes)
  find_callbacks_and_convert(after_callback_names, after_callback_changes)
end

There are some other edge cases that I didn’t cover here, e.g. if user defined a method password_changed?, I won’t convert it to saved_change_to_password? or will_save_change_to_password?. To get the full snippet code, please check it out here.