Module: ActiveRecord::Defaults::ClassMethods

Defined in:
lib/active_record/defaults.rb

Instance Method Summary collapse

Instance Method Details

#defaults(defaults, &block) ⇒ Object Also known as: default

Define default values for attributes on new records. Requires a hash of attribute => value pairs, or a single attribute with an associated block. If the value is a block, it will be called to retrieve the default value. If the value is a symbol, a method by that name will be called on the object to retrieve the default value.

The following code demonstrates the different ways default values can be specified. Defaults are applied in the order they are defined.

class Person < ActiveRecord::Base defaults :name => ‘My name’, :city => lambda { ‘My city’ }

default :birthdate do |person| Date.today if person.wants_birthday_today? end

default :favourite_colour => :default_favourite_colour

def default_favourite_colour “Blue” end end

The defaults and the default methods behave the same way. Use whichever is appropriate.

The default values are only used if the key is not present in the given attributes.

p = Person.new p.name # “My name” p.city # “My city”

p = Person.new(:name => nil) p.name # nil p.city # “My city”

Default values for belongs_to associations

Default values can also be specified for an association. For instance:

class Student < ActiveRecord::Base belongs_to :school default :school => lambda { School.new } end

In this scenario, if a school_id was provided in the attributes hash, the default value for the association will be ignored:

s = Student.new s.school # => #<School: …>

s = Student.new(:school_id => nil) s.school # => nil

Similarly, if a default value is specified for the foreign key and an object for the association is provided, the default foreign key is ignored.



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# File 'lib/active_record/defaults.rb', line 64

def defaults(defaults, &block)
  default_objects = case
    when defaults.is_a?(Hash)
      defaults.map { |attribute, value| Default.new(attribute, value) }
      
    when defaults.is_a?(Symbol) && block
      Default.new(defaults, block)
      
    else
      raise "pass either a hash of attribute/value pairs, or a single attribute with a block"
  end
  
  write_inheritable_array :attribute_defaults, [*default_objects]
end