Ariejan.net

Active Records provides callbacks, which is great is you want to perform extra business logic after (or before) saving, creating or destroying an instance of that model.

However, there are situations where you can easily fall into the trap of creating an infinite loop.

class Beer < ActiveRecord::Base
  def after_save
    x = some_magic_method(self)
    update_attribute(:my_attribute, x)
  end
end

The above will give you a nice infinite loop (which doesn’t scale). It’s possible to update your model, without calling the callbacks and without resorting to SQL.

class Beer < ActiveRecord::Base
  def after_save
    x = some_magic_method(self)
    Beer.update_all("my_attribute = #{x}", { :id => self.id })
  end
end

This is a bit unconventional, but it works nicely. You can use all the following ActiveRecord methods to update your model without calling callbacks:

• decrement
• decrement_counter
• delete
• delete_all
• find_by_sql
• increment
• increment_counter
• toggle
• update_all
• update_counters

An important warning: These methods don’t do all the nice SQL injection protection stuff you’re used to. In the example, the value of x will be inserted straight into the SQL. I recommend you only use these methods if you’re absolutely sure you’ve cleaned the values you’re inserting.

Check out the rails documentation on how to use these methods.

This entry was posted on Sunday, June 7th, 2009 at 22:25 and is filed under General. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.