What is the best way to set default values in ActiveRecord?

Question

What is the best way to 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

YUCK!

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.

What's the best way to set default value for fields in ActiveRecord model?

Answer 1

The Phusion guys have some nice plugin for this.

Answer 2

This is what constructors are for! Override the model's initialize method.

Use the after_initialize method.

Answer 3

class Item < ActiveRecord::Base
  def status
    self[:status] or ACTIVE
  end
end

Answer 4

We put the default values in the database through migrations (by specifying the :default option on each column definition) and let Active Record use these values to set the default for each attribute.

IMHO, this approach is aligned with the principles of AR : convention over configuration, DRY, the table definition drives the model, not the other way around.

Note that the defaults are still in the application (Ruby) code, though not in the model but in the migration(s).

Answer 5

Although doing that for setting default values is confusing and awkward in most cases, you can use :default_scope as well. Check out squil's comment here.

Answer 6

Sup guys, I ended up doing the following:

def after_initialize 
 self.extras||={}
 self.other_stuff||="This stuff"
end

Works like a charm!

Answer 7

after_initialize method is deprecated, use the callback instead.

after_initialize :defaults

def defaults
  self.extras||={}
  self.other_stuff||="This stuff"
end

however, using :default in your migrations is still the cleanest way.