How to save something to the database after failed ActiveRecord validations?

Question

Basically what I want to do is to log an action on MyModel in the table of MyModelLog. Here's some pseudo code:

class MyModel < ActiveRecord::Base
  validate :something

  def something
     # test
     errors.add(:data, "bug!!")
  end
end

I also have a model looking like this:

class MyModelLog < ActiveRecord::Base

  def self.log_something
    self.create(:log => "something happened")
  end

end

In order to log I tried to :

• Add MyModelLog.log_something in the something method of MyModel

• Call MyModelLog.log_something on the after_validation callback of MyModel

In both cases the creation is rolled back when the validation fails because it's in the validation transaction. Of course I also want to log when validations fail. I don't really want to log in a file or somewhere else than the database because I need the relationships of log entries with other models and ability to do requests.

What are my options?

Answer 1

Nested transactions do seem to work in MySQL.

Here is what I tried on a freshly generated rails (with MySQL) project:

./script/generate model Event title:string --skip-timestamps --skip-fixture

./script/generate model EventLog error_message:text --skip-fixture

class Event < ActiveRecord::Base                                                                                                                                       
  validates_presence_of :title                                                                                                                                         
  after_validation_on_create :log_errors                                                                                                                               

  def log_errors                                                                                                                                                       
    EventLog.log_error(self) if errors.on(:title).present?                                                                                                             
  end                                                                                                                                                                  
end  

class EventLog < ActiveRecord::Base                                                                                                                                    
  def self.log_error(event)                                                                                                                                            
    connection.execute('BEGIN') # If I do transaction do then it doesn't work.
    create :error_message => event.errors.on(:title)                                                                                            
    connection.execute('COMMIT')                                                                                                                                       
  end                                                                                                                                                                  
end 

# And then in script/console:
>> Event.new.save
=> false
>> EventLog.all
=> [#<EventLog id: 1, error_message: "can't be blank", created_at: "2010-10-22 13:17:41", updated_at: "2010-10-22 13:17:41">]
>> Event.all
=> []

Maybe I have over simplified it, or missing some point.