How to properly handle changed attributes in a Rails before_save hook?
I have a model that looks like this:
class StopWord < ActiveRecord::Base
UPDATE_KEYWORDS_BATCH_SIZE = 1000
before_save :update_keywords
def update_keywords
offset = 0
max_id = ((max_kw = Keyword.first(:order => 'id DESC')) and max_kw.id) || 0
while offset <= max_id
begin
conditions = ['id >= ? AND id < ? AND language = ? AND keyword RLIKE ?',
offset, offset + UPDATE_KEYWORDS_BATCH_SIZE, language]
# Clear keywords that matched the old stop word
if @changed_attributes and (old_stop_word = @changed_attributes['stop_word']) and not @new_record
Keyword.update_all 'stopword = 0', conditions + [old_stop_word]
end
Keyword.update_all 'stopword = 1', conditions + [stop_word]
rescue Exception => e
logger.error "Skipping batch of #{UPDATE_KEYWORDS_BATCH_SIZE} keywords at offset #{offset}"
logger.error "#{e.message}: #{e.backtrace.join "\n "}"
ensure
offset += UPDATE_KEYWORDS_BATCH_SIZE
end
end
end
end
This works just fine, as the unit tests show:
class KeywordStopWordTest < ActiveSupport::TestCase
def test_stop_word_applied_on_create
kw = Factory.create :keyword, :keyword => 'foo bar baz', :language => 'en'
assert !kw.stopword, 'keyword is not a stop word by default'
sw = Factory.create :stop_word, :stop_word => kw.keyword.split(' ')[1], :language => kw.language
kw.reload
assert kw.stopword, 'keyword is a stop word'
end
def test_stop_word_applied_on_save
kw = Factory.create :keyword, :keyword => 'foo bar baz', :language => 'en', :stopword => true
sw = Factory.create :keyword_stop_word, :stop_word => kw.keyword.split(' ')[1], :language => kw.language
sw.stop_word = 'blah'
sw.save
kw.reload
assert !kw.stopword, 'keyword is not a stop word'
end
end
But mucking with the @changed_attributes
instance variable just feels wrong. Is there a standard Rails-y way to get the old value of an attribute that is being modified on a save?
Update: Thanks to Douglas F Shearer and 开发者_开发技巧Simone Carletti (who apparently prefers Murphy's to Guinness), I have a cleaner solution:
def update_keywords
offset = 0
max_id = ((max_kw = Keyword.first(:order => 'id DESC')) and max_kw.id) || 0
while offset <= max_id
begin
conditions = ['id >= ? AND id < ? AND language = ? AND keyword RLIKE ?',
offset, offset + UPDATE_KEYWORDS_BATCH_SIZE, language]
# Clear keywords that matched the old stop word
if stop_word_changed? and not @new_record
Keyword.update_all 'stopword = 0', conditions + [stop_word_was]
end
Keyword.update_all 'stopword = 1', conditions + [stop_word]
rescue StandardError => e
logger.error "Skipping batch of #{UPDATE_KEYWORDS_BATCH_SIZE} keywords at offset #{offset}"
logger.error "#{e.message}: #{e.backtrace.join "\n "}"
ensure
offset += UPDATE_KEYWORDS_BATCH_SIZE
end
end
end
Thanks, guys!
You want ActiveModel::Dirty
.
Examples:
person = Person.find_by_name('Uncle Bob')
person.changed? # => false
person.name = 'Bob'
person.changed? # => true
person.name_changed? # => true
person.name_was # => 'Uncle Bob'
person.name_change # => ['Uncle Bob', 'Bob']
Full documentation: http://api.rubyonrails.org/classes/ActiveModel/Dirty.html
You're using the right feature but the wrong API.
You should #changes
and #changed?
.
See this article and the official API.
Two additional notes about your code:
- Never rescue Exception directly when you actually want to rescue execution errors. This is Java-style. You should rescue StandardError instead because lower errors are normally compilation error or system error.
You don't need the begin block in this case.
def update_keywords ... rescue => e ... ensure ... end
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