Ruby on Rails deep copy/ deep clone of object and its attributes

Question

I would like to do a deep copy on objects including all the attributes.

The experiment_old is has 10 trials. And I want to copy everything to experiment_new with the 10 trials. experiment_old should also keep the 10 trial info.

However, all the cases I tried below, they copy everything well, but experiment_old does not have the 10 trials info. They just show up on experiment_new.

What is the best way to do deep copy for these cases.

case 1:

@experiment_new = Experiment.create(@experiment_old.attributes.merge(:trials => experiment_old.trails))

case 2:

@experiment_new = Marshal.load(Marshal.dump(@experiment_old.trials))

case 3:

@experiment_new = @experiment_old.clone

Here is the model:

class Experiment < ActiveRecord::Base
  belongs_to :experimenter
  has_many :trials
  has_many :participants
end


class Trial < ActiveRecord::Base
  belongs_to :experiment
  belongs_to :datum
  belongs_to :condition
  has_one :result_trial
end

Answer 1

You may enjoy the Amoeba gem for ActiveRecord 3.2.

It supports easy and automatic recursive duplication of has_one, has_many and has_and_belongs_to_many associations, field preprocessing and a highly flexible and powerful configuration DSL that can be applied both to the model and on the fly.

be sure to check out the Amoeba Documentation but usage is pretty easy...

just

gem install amoeba

or add

gem 'amoeba'

to your Gemfile

then add the amoeba block to your model and run the dup method as usual

class Post < ActiveRecord::Base
  has_many :comments
  has_and_belongs_to_many :tags

  amoeba do
    enable
  end
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

class Tag < ActiveRecord::Base
  has_and_belongs_to_many :posts
end

class PostsController < ActionController
  def some_method
    my_post = Post.find(params[:id])
    new_post = my_post.dup
    new_post.save
  end
end

Your new post should have all the tags that were originally associated with it, and all the comments should be duplicated as well. You can disable the duplication of various records through the DSL, which you can read about in the documentation, but for example, if you wanted to keep the tags, but not the comments you could do something like this:

class Post < ActiveRecord::Base
  has_many :comments
  has_and_belongs_to_many :tags

  amoeba do
    include_field :comments
  end
end

or using the exclusive syntax

class Post < ActiveRecord::Base
  has_many :comments
  has_and_belongs_to_many :tags

  amoeba do
    exclude_field :comments
  end
end

or by specifying which field types to recognize (and thusly copy)

class Post < ActiveRecord::Base
  has_many :comments
  has_and_belongs_to_many :tags

  amoeba do
    recognize :has_and_belongs_to_many
  end
end

each of these various options should result in re-associating the new post with the same tags as the old post, but without duplicating the comments.

Amoeba will also automatically recurse in to child records if you enable them

class Post < ActiveRecord::Base
  has_many :comments

  amoeba do
    enable
  end
end

class Comment < ActiveRecord::Base
  belongs_to :post
  has_many :ratings

  amoeba do
    enable
  end
end

class Rating < ActiveRecord::Base
  belongs_to :comment
end

You can also prefix fields with some extra data to indicate uniqueness

class Post < ActiveRecord::Base
  has_many :comments

  amoeba do
    enable
    prepend :title => "Copy of "
  end
end

and in addition to prepend you can also append to or run a regex on a given field

Enjoy! :)