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 the controller.

Does anyone have any input if this is acceptable or if there's a better way to do it?

Answer 1

"Correct" is a dangerous word in Ruby. There's usually more than one way to do anything. If you know you'll always want that default value for that column on that table, setting them in a DB migration file is the easiest way:

class SetDefault < ActiveRecord::Migration   def self.up     change_column :people, :last_name, :type, :default => "Doe"   end    def self.down     # You can't currently remove default values in Rails     raise ActiveRecord::IrreversibleMigration, "Can't remove the default"   end end 

Because ActiveRecord autodiscovers your table and column properties, this will cause the same default to be set in any model using it in any standard Rails app.

However, if you only want default values set in specific cases -- say, it's an inherited model that shares a table with some others -- then another elegant way is do it directly in your Rails code when the model object is created:

class GenericPerson < Person   def initialize(attributes=nil)     attr_with_defaults = {:last_name => "Doe"}.merge(attributes)     super(attr_with_defaults)   end end 

Then, when you do a GenericPerson.new(), it'll always trickle the "Doe" attribute up to Person.new() unless you override it with something else.

Answer 2

Based on SFEley's answer, here is an updated/fixed one for newer Rails versions:

class SetDefault < ActiveRecord::Migration   def change     change_column :table_name, :column_name, :type, default: "Your value"   end end