How to set default values in Rails?

Question

I\'m trying to find the best way to set default values for objects in Rails.

The best I can think of is to set the default value in the new method in

Answer 1

In Ruby on Rails v3.2.8, using the after_initialize ActiveRecord callback, you can call a method in your model that will assign the default values for a new object.

after_initialize callback is triggered for each object that is found and instantiated by a finder, with after_initialize being triggered after new objects are instantiated as well (see ActiveRecord Callbacks).

So, IMO it should look something like:

class Foo < ActiveRecord::Base
  after_initialize :assign_defaults_on_new_Foo
  ...
  attr_accessible :bar
  ...
  private
  def assign_defaults_on_new_Foo
    # required to check an attribute for existence to weed out existing records
    self.bar = default_value unless self.attribute_whose_presence_has_been_validated
  end
end

Foo.bar = default_value for this instance unless the instance contains an attribute_whose_presence_has_been_validated previously on save/update. The default_value will then be used in conjunction with your view to render the form using the default_value for the bar attribute.

At best this is hacky...

EDIT - use 'new_record?' to check if instantiating from a new call

Instead of checking an attribute value, use the new_record? built-in method with rails. So, the above example should look like:

class Foo < ActiveRecord::Base
  after_initialize :assign_defaults_on_new_Foo, if: 'new_record?'
  ...
  attr_accessible :bar
  ...
  private
  def assign_defaults_on_new_Foo
    self.bar = default_value
  end
end

This is much cleaner. Ah, the magic of Rails - it's smarter than me.