Amoeba

Easy cloning of active_record objects including associations and several operations under associations and attributes.

What?

The goal was to be able to easily and quickly reproduce ActiveRecord objects including their children, for example copying a blog post maintaining its associated tags or categories.

This gem is named "Amoeba" because amoebas are (small life forms that are) good at reproducing. Their children and grandchildren also reproduce themselves quickly and easily.

Technical Details

An ActiveRecord extension gem to allow the duplication of associated child record objects when duplicating an active record model.

Rails 4.x, 5.0, 5.1 compatible.

Features

• Supports the following association types
  • has_many
  • has_one :through
  • has_many :through
  • has_and_belongs_to_many
• A simple DSL for configuration of which fields to copy. The DSL can be applied to your rails models or used on the fly.
• Supports STI (Single Table Inheritance) children inheriting their parent amoeba settings.
• Multiple configuration styles such as inclusive, exclusive and indiscriminate (aka copy everything).
• Supports cloning of the children of Many-to-Many records or merely maintaining original associations
• Supports automatic drill-down i.e. recursive copying of child and grandchild records.
• Supports preprocessing of fields to help indicate uniqueness and ensure the integrity of your data depending on your business logic needs, e.g. prepending "Copy of " or similar text.
• Supports preprocessing of fields with custom lambda blocks so you can do basically whatever you want if, for example, you need some custom logic while making copies.
• Amoeba can perform the following preprocessing operations on fields of copied records
  • set
  • prepend
  • append
  • nullify
  • customize
  • regex

Usage

Installation

is hopefully as you would expect:

gem install amoeba

or just add it to your Gemfile:

gem 'amoeba'

Configure your models with one of the styles below and then just run the amoeba_dup method on your model where you would run the dup method normally:

p = Post.create(:title => "Hello World!", :content => "Lorum ipsum dolor")
p.comments.create(:content => "I love it!")
p.comments.create(:content => "This sucks!")

puts Comment.all.count # should be 2

my_copy = p.amoeba_dup
my_copy.save

puts Comment.all.count # should be 4

By default, when enabled, amoeba will copy any and all associated child records automatically and associate them with the new parent record.

You can configure the behavior to only include fields that you list or to only include fields that you don't exclude. Of the three, the most performant will be the indiscriminate style, followed by the inclusive style, and the exclusive style will be the slowest because of the need for an extra explicit check on each field. This performance difference is likely negligible enough that you can choose the style to use based on which is easiest to read and write, however, if your data tree is large enough and you need control over what fields get copied, inclusive style is probably a better choice than exclusive style.

Configuration

Please note that these examples are only loose approximations of real world scenarios and may not be particularly realistic, they are only for the purpose of demonstrating feature usage.

Indiscriminate Style

This is the most basic usage case and will simply enable the copying of any known associations.

If you have some models for a blog about like this:

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

simply add the amoeba configuration block to your model and call the enable method to enable the copying of child records, like this:

class Post < ActiveRecord::Base
  has_many :comments

  amoeba do
    enable
  end
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

Child records will be automatically copied when you run the amoeba_dup method.

Inclusive Style

If you only want some of the associations copied but not others, you may use the inclusive style:

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

  amoeba do
    enable
    include_association :tags
    include_association :authors
  end
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

Using the inclusive style within the amoeba block actually implies that you wish to enable amoeba, so there is no need to run the enable method, though it won't hurt either:

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

  amoeba do
    include_association :tags
    include_association :authors
  end
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

You may also specify fields to be copied by passing an array. If you call the include_association with a single value, it will be appended to the list of already included fields. If you pass an array, your array will overwrite the original values.

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

  amoeba do
    include_association [:tags, :authors]
  end
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

These examples will copy the post's tags and authors but not its comments.

The inclusive style, when used, will automatically disable any other style that was previously selected.

Exclusive Style

If you have more fields to include than to exclude, you may wish to shorten the amount of typing and reading you need to do by using the exclusive style. All fields that are not explicitly excluded will be copied:

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

  amoeba do
    exclude_association :comments
  end
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

This example does the same thing as the inclusive style example, it will copy the post's tags and authors but not its comments. As with inclusive style, there is no need to explicitly enable amoeba when specifying fields to exclude.

The exclusive style, when used, will automatically disable any other style that was previously selected, so if you selected include fields, and then you choose some exclude fields, the exclude_association method will disable the previously selected inclusive style and wipe out any corresponding include fields.

Conditions

Also if you need to path extra condition for include or exclude relationship you can path method name to :if option.

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

  amoeba do
    include_association :comments, if: :popular?
  end
  
  def popular?
    likes > 15
  end
end

After call Post.first.amoeba_dup if likes is larger 15 than all comments will be duplicated too, but in another situation - no relations will be cloned. Same behavior will be for exclude_association.

Be aware! If you wrote:

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

  amoeba do
    exclude_association :tags
    include_association :comments, if: :popular?
  end
  
  def popular?
    likes > 15
  end
end

inclusion strategy will be chosen regardless of the result of popular? method call (the same for reverse situation).

Cloning

If you are using a Many-to-Many relationship, you may tell amoeba to actually make duplicates of the original related records rather than merely maintaining association with the original records. Cloning is easy, merely tell amoeba which fields to clone in the same way you tell it which fields to include or exclude.

class Post < ActiveRecord::Base
  has_and_belongs_to_many :warnings

  has_many :post_widgets
  has_many :widgets, :through => :post_widgets

  amoeba do
    enable
    clone [:widgets, :warnings]
  end
end

class Warning < ActiveRecord::Base
  has_and_belongs_to_many :posts
end

class PostWidget < ActiveRecord::Base
  belongs_to :widget
  belongs_to :post
end

class Widget < ActiveRecord::Base
  has_many :post_widgets
  has_many :posts, :through => :post_widgets
end

This example will actually duplicate the warnings and widgets in the database. If there were originally 3 warnings in the database then, upon duplicating a post, you will end up with 6 warnings in the database. This is in contrast to the default behavior where your new post would merely be re-associated with any previously existing warnings and those warnings themselves would not be duplicated.

Limiting Association Types

By default, amoeba recognizes and attempts to copy any children of the following association types:

• has one
• has many
• has and belongs to many

You may control which association types amoeba applies itself to by using the recognize method within the amoeba configuration block.

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

  amoeba do
    recognize [:has_one, :has_and_belongs_to_many]
  end
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

class Tag < ActiveRecord::Base
  has_and_belongs_to_many :posts
end

This example will copy the post's configuration data and keep tags associated with the new post, but will not copy the post's comments because amoeba will only recognize and copy children of has_one and has_and_belongs_to_many associations and in this example, comments are not an has_and_belongs_to_many association.

Field Preprocessors

Nullify

If you wish to prevent a regular (non has_* association based) field from retaining it's value when copied, you may "zero out" or "nullify" the field, like this:

class Topic < ActiveRecord::Base
  has_many :posts
end

class Post < ActiveRecord::Base
  belongs_to :topic
  has_many :comments

  amoeba do
    enable
    nullify :date_published
    nullify :topic_id
  end
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

This example will copy all of a post's comments. It will also nullify the publishing date and dissociate the post from its original topic.

Unlike inclusive and exclusive styles, specifying null fields will not automatically enable amoeba to copy all child records. As with any active record object, the default field value will be used instead of nil if a default value exists on the migration.

Set

If you wish to just set a field to an arbitrary value on all duplicated objects you may use the set directive. For example, if you wanted to copy an object that has some kind of approval process associated with it, you likely may wish to set the new object's state to be open or "in progress" again.

class Post < ActiveRecord::Base
  amoeba do
    set :state_tracker => "open_for_editing"
  end
end

In this example, when a post is duplicated, it's state_tracker field will always be given a value of open_for_editing to start.

Prepend

You may add a string to the beginning of a copied object's field during the copy phase:

class Post < ActiveRecord::Base
  amoeba do
    enable
    prepend :title => "Copy of "
  end
end

Append

You may add a string to the end of a copied object's field during the copy phase:

class Post < ActiveRecord::Base
  amoeba do
    enable
    append :title => "Copy of "
  end
end

Regex

You may run a search and replace query on a copied object's field during the copy phase:

class Post < ActiveRecord::Base
  amoeba do
    enable
    regex :contents => {:replace => /dog/, :with => 'cat'}
  end
end

Custom Methods

Customize

You may run a custom method or methods to do basically anything you like, simply pass a lambda block, or an array of lambda blocks to the customize directive. Each block must have the same form, meaning that each block must accept two parameters, the original object and the newly copied object. You may then do whatever you wish, like this:

class Post < ActiveRecord::Base
  amoeba do
    prepend :title => "Hello world! "

    customize(lambda { |original_post,new_post|
      if original_post.foo == "bar"
        new_post.baz = "qux"
      end
    })

    append :comments => "... know what I'm sayin?"
  end
end

or this, using an array:

class Post < ActiveRecord::Base
  has_and_belongs_to_many :tags

  amoeba do
    include_association :tags

    customize([
      lambda do |orig_obj,copy_of_obj|
        # good stuff goes here
      end,

      lambda do |orig_obj,copy_of_obj|
        # more good stuff goes here
      end
    ])
  end
end

Override

Lambda blocks passed to customize run, by default, after all copying and field pre-processing. If you wish to run a method before any customization or field pre-processing, you may use override the cousin of customize. Usage is the same as above.

class Post < ActiveRecord::Base
  amoeba do
    prepend :title => "Hello world! "

    override(lambda { |original_post,new_post|
      if original_post.foo == "bar"
        new_post.baz = "qux"
      end
    })

    append :comments => "... know what I'm sayin?"
  end
end

Chaining

You may apply a single preprocessor to multiple fields at once.

class Post < ActiveRecord::Base
  amoeba do
    enable
    prepend :title => "Copy of ", :contents => "Copied contents: "
  end
end

Stacking

You may apply multiple preprocessing directives to a single model at once.

class Post < ActiveRecord::Base
  amoeba do
    prepend :title => "Copy of ", :contents => "Original contents: "
    append :contents => " (copied version)"
    regex :contents => {:replace => /dog/, :with => 'cat'}
  end
end

This example should result in something like this:

post = Post.create(
  :title => "Hello world",
  :contents =>  "I like dogs, dogs are awesome."
)

new_post = post.amoeba_dup

new_post.title # "Copy of Hello world"
new_post.contents # "Original contents: I like cats, cats are awesome. (copied version)"

Like nullify, the preprocessing directives do not automatically enable the copying of associated child records. If only preprocessing directives are used and you do want to copy child records and no include_association or exclude_association list is provided, you must still explicitly enable the copying of child records by calling the enable method from within the amoeba block on your model.

Precedence

You may use a combination of configuration methods within each model's amoeba block. Recognized association types take precedence over inclusion or exclusion lists. Inclusive style takes precedence over exclusive style, and these two explicit styles take precedence over the indiscriminate style. In other words, if you list fields to copy, amoeba will only copy the fields you list, or only copy the fields you don't exclude as the case may be. Additionally, if a field type is not recognized it will not be copied, regardless of whether it appears in an inclusion list. If you want amoeba to automatically copy all of your child records, do not list any fields using either include_association or exclude_association.

The following example syntax is perfectly valid, and will result in the usage of inclusive style. The order in which you call the configuration methods within the amoeba block does not matter:

class Topic < ActiveRecord::Base
  has_many :posts
end

class Post < ActiveRecord::Base
  belongs_to :topic
  has_many :comments
  has_many :tags
  has_many :authors

  amoeba do
    exclude_association :authors
    include_association :tags
    nullify :date_published
    prepend :title => "Copy of "
    append :contents => " (copied version)"
    regex :contents => {:replace => /dog/, :with => 'cat'}
    include_association :authors
    enable
    nullify :topic_id
  end
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

This example will copy all of a post's tags and authors, but not its comments. It will also nullify the publishing date and dissociate the post from its original topic. It will also preprocess the post's fields as in the previous preprocessing example.

Note that, because of precedence, inclusive style is used and the list of exclude fields is never consulted. Additionally, the enable method is redundant because amoeba is automatically enabled when using include_association.

The preprocessing directives are run after child records are copied and are run in this order.

1. Null fields
2. Prepends
3. Appends
4. Search and Replace

Preprocessing directives do not affect inclusion and exclusion lists.

Recursing

You may cause amoeba to keep copying down the chain as far as you like, simply add amoeba blocks to each model you wish to have copy its children. Amoeba will automatically recurse into any enabled grandchildren and copy them as well.

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

In this example, when a post is copied, amoeba will copy each all of a post's comments and will also copy each comment's ratings.

Has One Through

Using the has_one :through association is simple, just be sure to enable amoeba on the each model with a has_one association and amoeba will automatically and recursively drill down, like so:

class Supplier < ActiveRecord::Base
  has_one :account
  has_one :history, :through => :account

  amoeba do
    enable
  end
end

class Account < ActiveRecord::Base
  belongs_to :supplier
  has_one :history

  amoeba do
    enable
  end
end

class History < ActiveRecord::Base
  belongs_to :account
end

Has Many Through

Copying of has_many :through associations works automatically. They perform the copy in the same way as the has_and_belongs_to_many association, meaning the actual child records are not copied, but rather the associations are simply maintained. You can add some field preprocessors to the middle model if you like but this is not strictly necessary:

class Assembly < ActiveRecord::Base
  has_many :manifests
  has_many :parts, :through => :manifests

  amoeba do
    enable
  end
end

class Manifest < ActiveRecord::Base
  belongs_to :assembly
  belongs_to :part

  amoeba do
    prepend :notes => "Copy of "
  end
end

class Part < ActiveRecord::Base
  has_many :manifests
  has_many :assemblies, :through => :manifests

  amoeba do
    enable
  end
end

On The Fly Configuration

You may control how amoeba copies your object, on the fly, by passing a configuration block to the model's amoeba method. The configuration method is static but the configuration is applied on a per instance basis.

class Post < ActiveRecord::Base
  has_many :comments

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

class Comment < ActiveRecord::Base
  belongs_to :post
end

class PostsController < ActionController
  def duplicate_a_post
    old_post = Post.create(
      :title => "Hello world",
      :contents => "Lorum ipsum"
    )

    old_post.class.amoeba do
      prepend :contents => "Here's a copy: "
    end

    new_post = old_post.amoeba_dup

    new_post.title # should be "Copy of Hello world"
    new_post.contents # should be "Here's a copy: Lorum ipsum"
    new_post.save
  end
end

Inheritance

If you are using the Single Table Inheritance provided by ActiveRecord, you may cause amoeba to automatically process child classes in the same way as their parents. All you need to do is call the propagate method within the amoeba block of the parent class and all child classes should copy in a similar manner.

create_table :products, :force => true do |t|
  t.string :type # this is the STI column

  # these belong to all products
  t.string :title
  t.decimal :price

  # these are for shirts only
  t.decimal :sleeve_length
  t.decimal :collar_size

  # these are for computers only
  t.integer :ram_size
  t.integer :hard_drive_size
end

class Product < ActiveRecord::Base
  has_many :images
  has_and_belongs_to_many :categories

  amoeba do
    enable
    propagate
  end
end

class Shirt < Product
end

class Computer < Product
end

class ProductsController
  def some_method
    my_shirt = Shirt.find(1)
    my_shirt.amoeba_dup
    my_shirt.save

    # this shirt should now:
    # - have its own copy of all parent images
    # - be in the same categories as the parent
  end
end

This example should duplicate all the images and sections associated with this Shirt, which is a child of Product

Parenting Style

By default, propagation uses submissive parenting, meaning the config settings on the parent will be applied, but any child settings, if present, will either add to or overwrite the parent settings depending on how you call the DSL methods.

You may change this behavior, the so called "parenting style", to give preference to the parent settings or to ignore any and all child settings.

Relaxed Parenting

The :relaxed parenting style will prefer parent settings.

class Product < ActiveRecord::Base
  has_many :images
  has_and_belongs_to_many :sections

  amoeba do
    exclude_association :images
    propagate :relaxed
  end
end

class Shirt < Product
  include_association :images
  include_association :sections
  prepend :title => "Copy of "
end

In this example, the conflicting include_association settings on the child will be ignored and the parent exclude_association setting will be used, while the prepend setting on the child will be honored because it doesn't conflict with the parent.

Strict Parenting

The :strict style will ignore child settings altogether and inherit any parent settings.

class Product < ActiveRecord::Base
  has_many :images
  has_and_belongs_to_many :sections

  amoeba do
    exclude_association :images
    propagate :strict
  end
end

class Shirt < Product
  include_association :images
  include_association :sections
  prepend :title => "Copy of "
end

In this example, the only processing that will happen when a Shirt is duplicated is whatever processing is allowed by the parent. So in this case the parent's exclude_association directive takes precedence over the child's include_association settings, and not only that, but none of the other settings for the child are used either. The prepend setting of the child is completely ignored.

Parenting and Precedence

Because of the two general forms of DSL config parameter usage, you may wish to make yourself mindful of how your coding style will affect the outcome of duplicating an object.

Just remember that:

• If you pass an array you will wipe all previous settings
• If you pass single values, you will add to currently existing settings

This means that, for example:

• When using the submissive parenting style, you can child take full precedence on a per field basis by passing an array of config values. This will cause the setting from the parent to be overridden instead of added to.
• When using the relaxed parenting style, you can still let the parent take precedence on a per field basis by passing an array of config values. This will cause the setting for that child to be overridden instead of added to.

A Submissive Override Example

This version will use both the parent and child settings, so both the images and sections will be copied.

class Product < ActiveRecord::Base
  has_many :images
  has_and_belongs_to_many :sections

  amoeba do
    include_association :images
    propagate
  end
end

class Shirt < Product
  include_association :sections
end

The next version will use only the child settings because passing an array will override any previous settings rather than adding to them and the child config takes precedence in the submissive parenting style. So in this case only the sections will be copied.

class Product < ActiveRecord::Base
  has_many :images
  has_and_belongs_to_many :sections

  amoeba do
    include_association :images
    propagate
  end
end

class Shirt < Product
  include_association [:sections]
end

A Relaxed Override Example

This version will use both the parent and child settings, so both the images and sections will be copied.

class Product < ActiveRecord::Base
  has_many :images
  has_and_belongs_to_many :sections

  amoeba do
    include_association :images
    propagate :relaxed
  end
end

class Shirt < Product
  include_association :sections
end

The next version will use only the parent settings because passing an array will override any previous settings rather than adding to them and the parent config takes precedence in the relaxed parenting style. So in this case only the images will be copied.

class Product < ActiveRecord::Base
  has_many :images
  has_and_belongs_to_many :sections

  amoeba do
    include_association [:images]
    propagate
  end
end

class Shirt < Product
  include_association :sections
end

Validating Nested Attributes

If you end up with some validation issues when trying to validate the presence of a child's belongs_to association, just be sure to include the :inverse_of declaration on your relationships and all should be well.

For example this will throw a validation error saying that your posts are invalid:

class Author < ActiveRecord::Base
  has_many :posts

  amoeba do
    enable
  end
end

class Post < ActiveRecord::Base
  belongs_to :author
  validates_presence_of :author

  amoeba do
    enable
  end
end

author = Author.find(1)
author.amoeba_dup

author.save # this will fail validation

Where this will work fine:

class Author < ActiveRecord::Base
  has_many :posts, :inverse_of => :author

  amoeba do
    enable
  end
end

class Post < ActiveRecord::Base
  belongs_to :author, :inverse_of => :posts
  validates_presence_of :author

  amoeba do
    enable
  end
end

author = Author.find(1)
author.amoeba_dup

author.save # this will pass validation

This issue is not amoeba specific and also occurs when creating new objects using accepts_nested_attributes_for, like this:

class Author < ActiveRecord::Base
  has_many :posts
  accepts_nested_attributes_for :posts
end

class Post < ActiveRecord::Base
  belongs_to :author
  validates_presence_of :author
end

# this will fail validation
author = Author.create({:name => "Jim Smith", :posts => [{:title => "Hello World", :contents => "Lorum ipsum dolor}]})

This issue with accepts_nested_attributes_for can also be solved by using :inverse_of, like this:

class Author < ActiveRecord::Base
  has_many :posts, :inverse_of => :author
  accepts_nested_attributes_for :posts
end

class Post < ActiveRecord::Base
  belongs_to :author, :inverse_of => :posts
  validates_presence_of :author
end

# this will pass validation
author = Author.create({:name => "Jim Smith", :posts => [{:title => "Hello World", :contents => "Lorum ipsum dolor}]})

The crux of the issue is that upon duplication, the new Author instance does not yet have an ID because it has not yet been persisted, so the :posts do not yet have an :author_id either, and thus no :author and thus they will fail validation. This issue may likely affect amoeba usage so if you get some validation failures, be sure to add :inverse_of to your models.

Cloning using custom method

If you need to clone model with custom method you can use through:

class ChildPrototype < ActiveRecord::Base
  amoeba do
    through :become_child
  end

  def become_child
    self.dup.becomes(Child)
  end
end

class Child < ChildPrototype
end

After cloning we will get instance of Child instead of ChildPrototype

Remapping associations

If you will need to do complex cloning with remapping associations name you can user remapper:

class ObjectPrototype < ActiveRecord::Base
  has_many :child_prototypes

  amoeba do
    method :become_real
    remapper :remap_associations
  end

  def become_real
    self.dup().becomes( RealObject )
  end

  def remap_associations( name )
    :childs if name == :child_prototypes
  end
end

class RealObject < ObjectPrototype
  has_many :childs
end

class ChildPrototype < ActiveRecord::Base
  amoeba do
    method :become_child
  end

  def become_child
    self.dup().becomes( Child )
  end
end

class Child < ChildPrototype
end

In result we will get next:

prototype = ObjectPrototype.new
prototype.child_prototypes << ChildPrototype.new
object = prototype.amoeba_dup
object.class # => RealObject
object.childs.first.class #=> Child

Configuration Reference

Here is a static reference to the available configuration methods, usable within the amoeba block on your rails models.

through

Set method what we will use for cloning model instead of dup.

for example:

amoeba do
  through :supper_pupper_dup
end

def supper_pupper_dup
  puts "multiplied by budding"
  self.dup
end

Controlling Associations

enable

Enables amoeba in the default style of copying all known associated child records. Using the enable method is only required if you wish to enable amoeba but you are not using either the include_association or exclude_association directives. If you use either inclusive or exclusive style, amoeba is automatically enabled for you, so calling enable would be redundant, though it won't hurt.

include_association

Adds a field to the list of fields which should be copied. All associations not in this list will not be copied. This method may be called multiple times, once per desired field, or you may pass an array of field names. Passing a single symbol will add to the list of included fields. Passing an array will empty the list and replace it with the array you pass.

exclude_association

Adds a field to the list of fields which should not be copied. Only the associations that are not in this list will be copied. This method may be called multiple times, once per desired field, or you may pass an array of field names. Passing a single symbol will add to the list of excluded fields. Passing an array will empty the list and replace it with the array you pass.

clone

Adds a field to the list of associations which should have their associated children actually cloned. This means for example, that instead of just maintaining original associations with previously existing tags, a copy will be made of each tag, and the new record will be associated with these new tag copies rather than the old tag copies. This method may be called multiple times, once per desired field, or you may pass an array of field names. Passing a single symbol will add to the list of excluded fields. Passing an array will empty the list and replace it with the array you pass.

propagate

This causes any inherited child models to take the same config settings when copied. This method may take up to one argument to control the so called "parenting style". The argument should be one of strict, relaxed or submissive.

The default "parenting style" is submissive

for example

amoeba do
  propagate :strict
end

will choose the strict parenting style of inherited settings.

raised

This causes any child to behave with a (potentially) different "parenting style" than its actual parent. This method takes up to a single parameter for which there are three options, strict, relaxed and submissive.

The default "parenting style" is submissive

for example:

amoeba do
  raised :relaxed
end

will choose the relaxed parenting style of inherited settings for this child. A parenting style set via the raised method takes precedence over the parenting style set using the propagate method.

remapper

Set the method what will be used for remapping of association name. Method will have one argument - association name as Symbol. If method will return nil then association will not be remapped.

for example:

amoeba do
  remapper :childs_to_parents
end

def childs_to_parents(association_name)
  :parents if association_name == :childs
end

Pre-Processing Fields

nullify

Adds a field to the list of non-association based fields which should be set to nil during copy. All fields in this list will be set to nil - note that any nullified field will be given its default value if a default value exists on this model's migration. This method may be called multiple times, once per desired field, or you may pass an array of field names. Passing a single symbol will add to the list of null fields. Passing an array will empty the list and replace it with the array you pass.

prepend

Prefix a field with some text. This only works for string fields. Accepts a hash of fields to prepend. The keys are the field names and the values are the prefix strings. An example scenario would be to add a string such as "Copy of " to your title field. Don't forget to include extra space to the right if you want it. Passing a hash will add each key value pair to the list of prepend directives. If you wish to empty the list of directives, you may pass the hash inside of an array like this [{:title => "Copy of "}].

append

Append some text to a field. This only works for string fields. Accepts a hash of fields to prepend. The keys are the field names and the values are the prefix strings. An example would be to add " (copied version)" to your description field. Don't forget to add a leading space if you want it. Passing a hash will add each key value pair to the list of append directives. If you wish to empty the list of directives, you may pass the hash inside of an array like this [{:contents => " (copied version)"}].

set

Set a field to a given value. This should work for almost any type of field. Accepts a hash of fields and the values you want them set to.. The keys are the field names and the values are the prefix strings. An example would be to add " (copied version)" to your description field. Don't forget to add a leading space if you want it. Passing a hash will add each key value pair to the list of append directives. If you wish to empty the list of directives, you may pass the hash inside of an array like this [{:approval_state => "open_for_editing"}].

regex

Globally search and replace the field for a given pattern. Accepts a hash of fields to run search and replace upon. The keys are the field names and the values are each a hash with information about what to find and what to replace it with. in the form of . An example would be to replace all occurrences of the word "dog" with the word "cat", the parameter hash would look like this :contents => {:replace => /dog/, :with => "cat"}. Passing a hash will add each key value pair to the list of regex directives. If you wish to empty the list of directives, you may pass the hash inside of an array like this [{:contents => {:replace => /dog/, :with => "cat"}].

override

Runs a custom method so you can do basically whatever you want. All you need to do is pass a lambda block or an array of lambda blocks that take two parameters, the original object and the new object copy. These blocks will run before any other duplication or field processing.

This method may be called multiple times, once per desired customizer block, or you may pass an array of lambdas. Passing a single lambda will add to the list of processing directives. Passing an array will empty the list and replace it with the array you pass.

customize

Runs a custom method so you can do basically whatever you want. All you need to do is pass a lambda block or an array of lambda blocks that take two parameters, the original object and the new object copy. These blocks will run after all copying and field processing.

This method may be called multiple times, once per desired customizer block, or you may pass an array of lambdas. Passing a single lambda will add to the list of processing directives. Passing an array will empty the list and replace it with the array you pass.

Known Limitations and Issues

The regular expression preprocessor uses case-sensitive String#gsub. Given the performance decreases inherrent in using regular expressions already, the fact that character classes can essentially account for case-insensitive searches, the desire to keep the DSL simple and the general use cases for this gem, I don't see a good reason to add yet more decision based conditional syntax to accommodate using case-insensitive searches or singular replacements with String#sub. If you find yourself wanting either of these features, by all means fork the code base and if you like your changes, submit a pull request.

The behavior when copying nested hierarchical models is undefined. Copying a category model which has a parent_id field pointing to the parent category, for example, is currently undefined.

The behavior when copying polymorphic has_many associations is also undefined. Support for these types of associations is planned for a future release.

For Developers

You may run the rspec tests like this:

bundle exec rspec spec

TODO

• add ability to cancel further processing from within an override block
• write some spec for the override method

License

The BSD License

Copyright (c) 2012, Vaughn Draughon All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.