Active Record automatically timestamps create and update operations if the table has fields named created_at/created_on or updated_at/updated_on.

Timestamping can be turned off by setting 

  <tt>ActiveRecord::Base.record_timestamps = false</tt>

Timestamps are in the local timezone by default but you can use UTC by setting 

  <tt>ActiveRecord::Base.default_timezone = :utc</tt>
Methods
Public Instance methods
touch(attribute = nil)

Saves the record with the updated_at/on attributes set to the current time. If the save fails because of validation errors, an ActiveRecord::RecordInvalid exception is raised. If an attribute name is passed, that attribute is used for the touch instead of the updated_at/on attributes.

Examples: 

  product.touch               # updates updated_at
  product.touch(:designed_at) # updates the designed_at attribute

[ show source ]

    # File activerecord/lib/active_record/timestamp.rb, line 27
27:     def touch(attribute = nil)
28:       current_time = current_time_from_proper_timezone
29: 
30:       if attribute
31:         write_attribute(attribute, current_time)
32:       else
33:         write_attribute('updated_at', current_time) if respond_to?(:updated_at)
34:         write_attribute('updated_on', current_time) if respond_to?(:updated_on)
35:       end
36: 
37:       save!
38:     end