How can I set default values in ActiveRecord?

Question

How can I set default value in ActiveRecord?

I see a post from Pratik that describes an ugly, complicated chunk of code: http://m.onkey.org/2007/7/24/how-to-set-default-values-in-your-model

class Item < ActiveRecord::Base  
  def initialize_with_defaults(attrs = nil, &block)
    initialize_without_defaults(attrs) do
      setter = lambda { |key, value| self.send("#{key.to_s}=", value) unless
        !attrs.nil? && attrs.keys.map(&:to_s).include?(key.to_s) }
      setter.call('scheduler_type', 'hotseat')
      yield self if block_given?
    end
  end
  alias_method_chain :initialize, :defaults
end

I have seen the following examples googling around:

  def initialize 
    super
    self.status = ACTIVE unless self.status
  end

and

  def after_initialize 
    return unless new_record?
    self.status = ACTIVE
  end

I've also seen people put it in their migration, but I'd rather see it defined in the model code.

Is there a canonical way to set default value for fields in ActiveRecord model?

Answer 1

The problem with the after_initialize solutions is that you have to add an after_initialize to every single object you look up out of the DB, regardless of whether you access this attribute or not. I suggest a lazy-loaded approach.

The attribute methods (getters) are of course methods themselves, so you can override them and provide a default. Something like:

Class Foo < ActiveRecord::Base
  # has a DB column/field atttribute called 'status'
  def status
    (val = read_attribute(:status)).nil? ? 'ACTIVE' : val
  end
end

Unless, like someone pointed out, you need to do Foo.find_by_status('ACTIVE'). In that case I think you'd really need to set the default in your database constraints, if the DB supports it.