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

For boolean fields in Rails 3.2.6 at least, this will work in your migration.

def change
  add_column :users, :eula_accepted, :boolean, default: false
end

Putting a 1 or 0 for a default will not work here, since it is a boolean field. It must be a true or false value.

Answer 2

Generate a migration and use change_column_default, is succinct and reversible:

class SetDefaultAgeInPeople < ActiveRecord::Migration[5.2]
  def change
    change_column_default :people, :age, { from: nil, to: 0 }
  end
end

Answer 3

If you are referring to ActiveRecord objects, you have (more than) two ways of doing this:

1. Use a :default parameter in the DB

E.G.

class AddSsl < ActiveRecord::Migration
  def self.up
    add_column :accounts, :ssl_enabled, :boolean, :default => true
  end

  def self.down
    remove_column :accounts, :ssl_enabled
  end
end

More info here: http://api.rubyonrails.org/classes/ActiveRecord/Migration.html

2. Use a callback

E.G. before_validation_on_create

More info here: http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html#M002147

Answer 4

A potentially even better/cleaner potential way than the answers proposed is to overwrite the accessor, like this:

def status
  self['name_of_var'] || 'desired_default_value'
end

See "Overwriting default accessors" in the ActiveRecord::Base documentation and more from StackOverflow on using self.

Answer 5

The suggestion to override new/initialize is probably incomplete. Rails will (frequently) call allocate for ActiveRecord objects, and calls to allocate won't result in calls to initialize.

If you're talking about ActiveRecord objects, take a look at overriding after_initialize.

These blog posts (not mine) are useful:

Default values Default constructors not called

[Edit: SFEley points out that Rails actually does look at the default in the database when it instantiates a new object in memory - I hadn't realized that.]

Answer 6

You can also try change_column_default in your migrations (tested in Rails 3.2.8):

class SetDefault < ActiveRecord::Migration
  def up
    # Set default value
    change_column_default :people, :last_name, "Smith"
  end

  def down
    # Remove default
    change_column_default :people, :last_name, nil
  end
end

change_column_default Rails API docs