What is the easiest way to duplicate an activerecord record?

To get a copy, use the dup (or clone for < rails 3.1+) method:

#rails >= 3.1
new_record = old_record.dup

# rails < 3.1
new_record = old_record.clone

Then you can change whichever fields you want.

ActiveRecord overrides the built-in Object#clone to give you a new (not saved to the DB) record with an unassigned ID.
Note that it does not copy associations, so you'll have to do this manually if you need to.

Rails 3.1 clone is a shallow copy, use dup instead...

Depending on your needs and programming style, you can also use a combination of the new method of the class and merge. For lack of a better simple example, suppose you have a task scheduled for a certain date and you want to duplicate it to another date. The actual attributes of the task aren't important, so:

old_task = Task.find(task_id)
new_task = Task.new(old_task.attributes.merge({:scheduled_on => some_new_date}))

will create a new task with :id => nil, :scheduled_on => some_new_date, and all other attributes the same as the original task. Using Task.new, you will have to explicitly call save, so if you want it saved automatically, change Task.new to Task.create.

Peace.

I usually just copy the attributes, changing whatever I need changing:

new_user = User.new(old_user.attributes.merge(:login => "newlogin"))

In Rails 5 you can simply create duplicate object or record like this.

new_user = old_user.dup

Here is a sample of overriding ActiveRecord #dup method to customize instance duplication and include relation duplication as well:

class Offer < ApplicationRecord
  has_many :offer_items

  def dup
    super.tap do |new_offer|

      # change title of the new instance
      new_offer.title = "Copy of #{@offer.title}"

      # duplicate offer_items as well
      self.offer_items.each { |offer_item| new_offer.offer_items << offer_item.dup }
    end
  end
end

Note: this method doesn't require any external gem but it requires newer ActiveRecord version with #dup method implemented

Try rails's dup method:

new_record = old_record.dup.save