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 case you're dealing with a Model, you can use the Attriutes API in Rails 5+ http://api.rubyonrails.org/classes/ActiveRecord/Attributes/ClassMethods.html#method-i-attribute

just add a migration with a proper column name and then in the model set it with:

class StoreListing < ActiveRecord::Base
  attribute :country, :string, default: 'PT'
end

Answer 2

First of all you can't overload initialize(*args) as it's not called in all cases.

Your best option is to put your defaults into your migration:

add_column :accounts, :max_users, :integer, :default => 10

Second best is to place defaults into your model but this will only work with attributes that are initially nil. You may have trouble as I did with boolean columns:

def after_initialize
  if new_record?
    max_users ||= 10
  end
end

You need the new_record? so the defaults don't override values loaded from the datbase.

You need ||= to stop Rails from overriding parameters passed into the initialize method.

Answer 3

You can override the constructor for the ActiveRecord model.

Like this:

def initialize(*args)
  super(*args)
  self.attribute_that_needs_default_value ||= default_value
  self.attribute_that_needs_another_default_value ||= another_default_value
  #ad nauseum
end

Answer 4

You could use the rails_default_value gem. eg:

class Foo < ActiveRecord::Base
  # ...
  default :bar => 'some default value'
  # ...
end

https://github.com/keithrowell/rails_default_value

Answer 5

If you're talking about ActiveRecord objects, I use the 'attribute-defaults' gem.

Documentation & download: https://github.com/bsm/attribute-defaults