paper-trail-gem--paper_trail/README.md

PaperTrail

Track changes to your models, for auditing or versioning. See how a model looked at any stage in its lifecycle, revert it to any version, or restore it after it has been destroyed.

• Features
• Compatibility
• Installation
• API Summary
• Basic Usage
• Limiting What is Versioned, and When
  • Choosing Lifecycle Events To Monitor
  • Choosing When To Save New Versions
  • Choosing Attributes To Monitor
  • Turning PaperTrail Off/On
  • Limiting the Number of Versions Created
• Working With Versions
  • Reverting And Undeleting A Model
  • Navigating Versions
  • Diffing Versions
  • Deleting Old Versions
• Finding Out Who Was Responsible For A Change
• Custom Version Classes
• Associations
• Storing metadata
• Using a custom serializer
• SerializedAttributes support
• Testing

Features

• Stores create, update and destroy events
  • Does not store updates which don't change anything
  • Support for versioning associated records
• Can store metadata with each version record
  • Who was responsible for a change
  • Arbitrary model-level metadata (useful for filtering versions)
  • Arbitrary controller-level information e.g. remote IP
• Configurable
  • No configuration necessary, but if you want to ..
  • Configure which events (create, update and destroy) are versioned
  • Configure which attributes must change for an update to be versioned
  • Turn off/on by model, request, or globally
  • Use separate tables for separate models
• Extensible
  • Write a custom version class for complete control
  • Write custom version classes for each of your models
• Work with versions
  • Restore any version, including the original, even once destroyed
  • Restore any version even if the schema has since changed
  • Restore the version as of a particular time
• Thoroughly tested
• Threadsafe

Compatibility

paper_trail	branch	tags	ruby	activerecord
5 (unreleased)	master	none	>= 1.9.3	>= 3.0, < 6
4	4.0-stable	v4.x	>= 1.8.7	>= 3.0, < 6
3	3.0-stable	v3.x	>= 1.8.7	>= 3.0, < 5
2	2.7-stable	v2.x	>= 1.8.7	>= 3.0, < 4
1	rails2	v1.x	>= 1.8.7	>= 2.3, < 3

Installation

Rails 3 and 4

1. Add PaperTrail to your Gemfile.

   gem 'paper_trail', '~> 4.0.0'

2. Generate a migration which will add a versions table to your database.

   bundle exec rails generate paper_trail:install

3. Run the migration.

   bundle exec rake db:migrate

4. Add has_paper_trail to the models you want to track.

Sinatra

In order to configure PaperTrail for usage with Sinatra, your Sinatra app must be using ActiveRecord 3 or 4. It is also recommended to use the Sinatra ActiveRecord Extension or something similar for managing your applications ActiveRecord connection in a manner similar to the way Rails does. If using the aforementioned Sinatra ActiveRecord Extension, steps for setting up your app with PaperTrail will look something like this:

1. Add PaperTrail to your Gemfile.

   gem 'paper_trail', '~> 4.0.0'

2. Generate a migration to add a versions table to your database.

   bundle exec rake db:create_migration NAME=create_versions

3. Copy contents of create_versions.rb into the create_versions migration that was generated into your db/migrate directory.

4. Run the migration.

   bundle exec rake db:migrate

5. Add has_paper_trail to the models you want to track.

PaperTrail provides a helper extension that acts similar to the controller mixin it provides for Rails applications.

It will set PaperTrail.whodunnit to whatever is returned by a method named user_for_paper_trail which you can define inside your Sinatra Application. (by default it attempts to invoke a method named current_user)

If you're using the modular Sinatra::Base style of application, you will need to register the extension:

# bleh_app.rb
require 'sinatra/base'

class BlehApp < Sinatra::Base
  register PaperTrail::Sinatra
end

API Summary

When you declare has_paper_trail in your model, you get these methods:

class Widget < ActiveRecord::Base
  has_paper_trail
end

# Returns this widget's versions.  You can customise the name of the
# association.
widget.versions

# Return the version this widget was reified from, or nil if it is live.
# You can customise the name of the method.
widget.version

# Returns true if this widget is the current, live one; or false if it is from
# a previous version.
widget.live?

# Returns who put the widget into its current state.
widget.paper_trail_originator

# Returns the widget (not a version) as it looked at the given timestamp.
widget.version_at(timestamp)

# Returns the widget (not a version) as it was most recently.
widget.previous_version

# Returns the widget (not a version) as it became next.
widget.next_version

# Generates a version for a `touch` event (`widget.touch` does NOT generate a
# version)
widget.touch_with_version

# Turn PaperTrail off for all widgets.
Widget.paper_trail_off!

# Turn PaperTrail on for all widgets.
Widget.paper_trail_on!

# Is PaperTrail enabled for Widget, the class?
Widget.paper_trail_enabled_for_model?

# Is PaperTrail enabled for widget, the instance?
widget.paper_trail_enabled_for_model?

And a PaperTrail::Version instance has these methods:

# Returns the item restored from this version.
version.reify(options = {})

# Return a new item from this version
version.reify(dup: true)

# Returns who put the item into the state stored in this version.
version.paper_trail_originator

# Returns who changed the item from the state it had in this version.
version.terminator
version.whodunnit
version.version_author

# Returns the next version.
version.next

# Returns the previous version.
version.previous

# Returns the index of this version in all the versions.
version.index

# Returns the event that caused this version (create|update|destroy).
version.event

# Query versions objects by attributes.
PaperTrail::Version.where_object(attr1: val1, attr2: val2)

# Query versions object_changes field by attributes (requires
# `object_changes` column on versions table).
# Also can't guarantee consistent query results for numeric values
# due to limitations of SQL wildcard matchers against the serialized objects.
PaperTrail::Version.where_object_changes(attr1: val1)

In your controllers you can override these methods:

# Returns the user who is responsible for any changes that occur.
# Defaults to current_user.
user_for_paper_trail

# Returns any information about the controller or request that you want
# PaperTrail to store alongside any changes that occur.
info_for_paper_trail

Basic Usage

PaperTrail is simple to use. Just add 15 characters to a model to get a paper trail of every create, update, and destroy.

class Widget < ActiveRecord::Base
  has_paper_trail
end

This gives you a versions method which returns the paper trail of changes to your model.

widget = Widget.find 42
widget.versions
# [<PaperTrail::Version>, <PaperTrail::Version>, ...]

Once you have a version, you can find out what happened:

v = widget.versions.last
v.event                     # 'update' (or 'create' or 'destroy')
v.whodunnit                 # '153'  (if the update was via a controller and
                            #         the controller has a current_user method,
                            #         here returning the id of the current user)
v.created_at                # when the update occurred
widget = v.reify            # the widget as it was before the update;
                            # would be nil for a create event

PaperTrail stores the pre-change version of the model, unlike some other auditing/versioning plugins, so you can retrieve the original version. This is useful when you start keeping a paper trail for models that already have records in the database.

widget = Widget.find 153
widget.name                                 # 'Doobly'

# Add has_paper_trail to Widget model.

widget.versions                             # []
widget.update_attributes :name => 'Wotsit'
widget.versions.last.reify.name             # 'Doobly'
widget.versions.last.event                  # 'update'

This also means that PaperTrail does not waste space storing a version of the object as it currently stands. The versions method gives you previous versions; to get the current one just call a finder on your Widget model as usual.

Here's a helpful table showing what PaperTrail stores:

Event	create	update	destroy
Model Before	nil	widget	widget
Model After	widget	widget	nil

PaperTrail stores the values in the Model Before column. Most other auditing/versioning plugins store the After column.

Choosing Lifecycle Events To Monitor

You can choose which events to track with the on option. For example, to ignore create events:

class Article < ActiveRecord::Base
  has_paper_trail :on => [:update, :destroy]
end

has_paper_trail installs callbacks for these lifecycle events. If there are other callbacks in your model, their order relative to those installed by PaperTrail may matter, so be aware of any potential interactions.

You may also have the PaperTrail::Version model save a custom string in it's event field instead of the typical create, update, destroy. PaperTrail supplies a custom accessor method called paper_trail_event, which it will attempt to use to fill the event field before falling back on one of the default events.

a = Article.create
a.versions.size                           # 1
a.versions.last.event                     # 'create'
a.paper_trail_event = 'update title'
a.update_attributes :title => 'My Title'
a.versions.size                           # 2
a.versions.last.event                     # 'update title'
a.paper_trail_event = nil
a.update_attributes :title => "Alternate"
a.versions.size                           # 3
a.versions.last.event                     # 'update'

Choosing When To Save New Versions

You can choose the conditions when to add new versions with the if and unless options. For example, to save versions only for US non-draft translations:

class Translation < ActiveRecord::Base
  has_paper_trail :if     => Proc.new { |t| t.language_code == 'US' },
                  :unless => Proc.new { |t| t.type == 'DRAFT'       }
end

Choosing Attributes To Monitor

You can ignore changes to certain attributes like this:

class Article < ActiveRecord::Base
  has_paper_trail :ignore => [:title, :rating]
end

This means that changes to just the title or rating will not store another version of the article. It does not mean that the title and rating attributes will be ignored if some other change causes a new PaperTrail::Version to be created. For example:

a = Article.create
a.versions.length                         # 1
a.update_attributes :title => 'My Title', :rating => 3
a.versions.length                         # 1
a.update_attributes :title => 'Greeting', :content => 'Hello'
a.versions.length                         # 2
a.previous_version.title                  # 'My Title'

Or, you can specify a list of all attributes you care about:

class Article < ActiveRecord::Base
  has_paper_trail :only => [:title]
end

This means that only changes to the title will save a version of the article:

a = Article.create
a.versions.length                         # 1
a.update_attributes :title => 'My Title'
a.versions.length                         # 2
a.update_attributes :content => 'Hello'
a.versions.length                         # 2
a.previous_version.content                # nil

The :ignore and :only options can also accept Hash arguments, where the :

class Article < ActiveRecord::Base
  has_paper_trail :only => [:title => Proc.new { |obj| !obj.title.blank? } ]
end

This means that if the title is not blank, then only changes to the title will save a version of the article:

a = Article.create
a.versions.length                         # 1
a.update_attributes :content => 'Hello'
a.versions.length                         # 2
a.update_attributes :title => 'My Title'
a.versions.length                         # 3
a.update_attributes :content => 'Hai'
a.versions.length                         # 3
a.previous_version.content                # "Hello"
a.update_attributes :title => 'Dif Title'
a.versions.length                         # 4
a.previous_version.content                # "Hai"

Passing both :ignore and :only options will result in the article being saved if a changed attribute is included in :only but not in :ignore.

You can skip fields altogether with the :skip option. As with :ignore, updates to these fields will not create a new PaperTrail::Version. In addition, these fields will not be included in the serialized version of the object whenever a new PaperTrail::Version is created.

For example:

class Article < ActiveRecord::Base
  has_paper_trail :skip => [:file_upload]
end

Turning PaperTrail Off/On

Sometimes you don't want to store changes. Perhaps you are only interested in changes made by your users and don't need to store changes you make yourself in, say, a migration -- or when testing your application.

You can turn PaperTrail on or off in three ways: globally, per request, or per class.

Globally

On a global level you can turn PaperTrail off like this:

PaperTrail.enabled = false

For example, you might want to disable PaperTrail in your Rails application's test environment to speed up your tests. This will do it (note: this gets done automatically for RSpec and Cucumber, please see the Testing section):

# in config/environments/test.rb
config.after_initialize do
  PaperTrail.enabled = false
end

If you disable PaperTrail in your test environment but want to enable it for specific tests, you can add a helper like this to your test helper:

# in test/test_helper.rb
def with_versioning
  was_enabled = PaperTrail.enabled?
  was_enabled_for_controller = PaperTrail.enabled_for_controller?
  PaperTrail.enabled = true
  PaperTrail.enabled_for_controller = true
  begin
    yield
  ensure
    PaperTrail.enabled = was_enabled
    PaperTrail.enabled_for_controller = was_enabled_for_controller
  end
end

And then use it in your tests like this:

test "something that needs versioning" do
  with_versioning do
    # your test
  end
end

Per request

You can turn PaperTrail on or off per request by adding a paper_trail_enabled_for_controller method to your controller which returns true or false:

class ApplicationController < ActionController::Base
  def paper_trail_enabled_for_controller
    request.user_agent != 'Disable User-Agent'
  end
end

Per class

If you are about to change some widgets and you don't want a paper trail of your changes, you can turn PaperTrail off like this:

Widget.paper_trail_off!

And on again like this:

Widget.paper_trail_on!

Per method call

You can call a method without creating a new version using without_versioning. It takes either a method name as a symbol:

@widget.without_versioning :destroy

Or a block:

@widget.without_versioning do
  @widget.update_attributes :name => 'Ford'
end

Limiting the Number of Versions Created

Configure version_limit to cap the number of versions saved per record. This does not apply to create events.

# Limit: 4 versions per record (3 most recent, plus a `create` event)
PaperTrail.config.version_limit = 3
# Remove the limit
PaperTrail.config.version_limit = nil

Reverting And Undeleting A Model

PaperTrail makes reverting to a previous version easy:

widget = Widget.find 42
widget.update_attributes :name => 'Blah blah'
# Time passes....
widget = widget.previous_version  # the widget as it was before the update
widget.save                       # reverted

Alternatively you can find the version at a given time:

widget = widget.version_at(1.day.ago)  # the widget as it was one day ago
widget.save                            # reverted

Note version_at gives you the object, not a version, so you don't need to call reify.

Undeleting is just as simple:

widget = Widget.find 42
widget.destroy
# Time passes....
widget = PaperTrail::Version.find(153).reify  # the widget as it was before destruction
widget.save                         # the widget lives!

You could even use PaperTrail to implement an undo system, Ryan Bates has!

If your model uses optimistic locking don't forget to increment your lock_version before saving or you'll get a StaleObjectError.

Navigating Versions

You can call previous_version and next_version on an item to get it as it was/became. Note that these methods reify the item for you.

live_widget = Widget.find 42
live_widget.versions.length           # 4 for example
widget = live_widget.previous_version # => widget == live_widget.versions.last.reify
widget = widget.previous_version      # => widget == live_widget.versions[-2].reify
widget = widget.next_version          # => widget == live_widget.versions.last.reify
widget.next_version                   # live_widget

If instead you have a particular version of an item you can navigate to the previous and next versions.

widget = Widget.find 42
version = widget.versions[-2]    # assuming widget has several versions
previous = version.previous
next = version.next

You can find out which of an item's versions yours is:

current_version_number = version.index    # 0-based

If you got an item by reifying one of its versions, you can navigate back to the version it came from:

latest_version = Widget.find(42).versions.last
widget = latest_version.reify
widget.version == latest_version    # true

You can find out whether a model instance is the current, live one -- or whether it came instead from a previous version -- with live?:

widget = Widget.find 42
widget.live?                        # true
widget = widget.previous_version
widget.live?                        # false

And you can perform WHERE queries for object versions based on attributes:

# All versions that meet these criteria.
PaperTrail::Version.where_object(content: "Hello", title: "Article")

Diffing Versions

There are two scenarios: diffing adjacent versions and diffing non-adjacent versions.

The best way to diff adjacent versions is to get PaperTrail to do it for you. If you add an object_changes text column to your versions table, either at installation time with the rails generate paper_trail:install --with-changes option or manually, PaperTrail will store the changes diff (excluding any attributes PaperTrail is ignoring) in each update version. You can use the version.changeset method to retrieve it. For example:

widget = Widget.create :name => 'Bob'
widget.versions.last.changeset
# {
#   "name"=>[nil, "Bob"],
#   "created_at"=>[nil, 2015-08-10 04:10:40 UTC],
#   "updated_at"=>[nil, 2015-08-10 04:10:40 UTC],
#   "id"=>[nil, 1]
# }
widget.update_attributes :name => 'Robert'
widget.versions.last.changeset
# {
#   "name"=>["Bob", "Robert"],
#   "updated_at"=>[2015-08-10 04:13:19 UTC, 2015-08-10 04:13:19 UTC]
# }
widget.destroy
widget.versions.last.changeset
# {}

The object_changes are only stored for creation and updates, not when an object is destroyed.

Please be aware that PaperTrail doesn't use diffs internally. When I designed PaperTrail I wanted simplicity and robustness so I decided to make each version of an object self-contained. A version stores all of its object's data, not a diff from the previous version. This means you can delete any version without affecting any other.

To diff non-adjacent versions you'll have to write your own code. These libraries may help:

For diffing two strings:

• htmldiff: expects but doesn't require HTML input and produces HTML output. Works very well but slows down significantly on large (e.g. 5,000 word) inputs.
• differ: expects plain text input and produces plain text/coloured/HTML/any output. Can do character-wise, word-wise, line-wise, or arbitrary-boundary-string-wise diffs. Works very well on non-HTML input.
• diff-lcs: old-school, line-wise diffs.

For diffing two ActiveRecord objects:

• Jeremy Weiskotten's PaperTrail fork: uses ActiveSupport's diff to return an array of hashes of the changes.
• activerecord-diff: rather like ActiveRecord::Dirty but also allows you to specify which columns to compare.

If you wish to selectively record changes for some models but not others you can opt out of recording changes by passing :save_changes => false to your has_paper_trail method declaration.

Deleting Old Versions

Over time your versions table will grow to an unwieldy size. Because each version is self-contained (see the Diffing section above for more) you can simply delete any records you don't want any more. For example:

sql> delete from versions where created_at < 2010-06-01;

PaperTrail::Version.delete_all ["created_at < ?", 1.week.ago]

Finding Out Who Was Responsible For A Change

Set PaperTrail.whodunnit=, and that value will be stored in the version's whodunnit column.

PaperTrail.whodunnit = 'Andy Stewart'
widget.update_attributes :name => 'Wibble'
widget.versions.last.whodunnit              # Andy Stewart

If your controller has a current_user method, PaperTrail provides a before_filter that will assign current_user.id to PaperTrail.whodunnit. You can add this before_filter to your ApplicationController.

class ApplicationController
  before_filter :set_paper_trail_whodunnit
end

You may want set_paper_trail_whodunnit to call a different method to find out who is responsible. To do so, override the user_for_paper_trail method in your controller like this:

class ApplicationController
  def user_for_paper_trail
    logged_in? ? current_member.id : 'Public user'  # or whatever
  end
end

See also: Setting whodunnit in the rails console

Sometimes you want to define who is responsible for a change in a small scope without overwriting value of PaperTrail.whodunnit. It is possible to define the whodunnit value for an operation inside a block like this:

PaperTrail.whodunnit = 'Andy Stewart'
widget.whodunnit('Lucas Souza') do
  widget.update_attributes :name => 'Wibble'
end
widget.versions.last.whodunnit              # Lucas Souza
widget.update_attributes :name => 'Clair'
widget.versions.last.whodunnit              # Andy Stewart
widget.whodunnit('Ben Atkins') { |w| w.update_attributes :name => 'Beth' } # this syntax also works
widget.versions.last.whodunnit              # Ben Atkins

A version's whodunnit records who changed the object causing the version to be stored. Because a version stores the object as it looked before the change (see the table above), whodunnit returns who stopped the object looking like this -- not who made it look like this. Hence whodunnit is aliased as terminator.

To find out who made a version's object look that way, use version.paper_trail_originator. And to find out who made a "live" object look like it does, call paper_trail_originator on the object.

widget = Widget.find 153                    # assume widget has 0 versions
PaperTrail.whodunnit = 'Alice'
widget.update_attributes :name => 'Yankee'
widget..paper_trail_originator              # 'Alice'
PaperTrail.whodunnit = 'Bob'
widget.update_attributes :name => 'Zulu'
widget.paper_trail_originator               # 'Bob'
first_version, last_version = widget.versions.first, widget.versions.last
first_version.whodunnit                     # 'Alice'
first_version.paper_trail_originator        # nil
first_version.terminator                    # 'Alice'
last_version.whodunnit                      # 'Bob'
last_version.paper_trail_originator         # 'Alice'
last_version.terminator                     # 'Bob'

Custom Version Classes

You can specify custom version subclasses with the :class_name option:

class PostVersion < PaperTrail::Version
  # custom behaviour, e.g:
  self.table_name = :post_versions
end

class Post < ActiveRecord::Base
  has_paper_trail :class_name => 'PostVersion'
end

Unlike ActiveRecord's class_name, you'll have to supply the complete module path to the class (e.g. Foo::BarVersion if your class is inside the module Foo).

Advantages

1. For models which have a lot of versions, storing each model's versions in a separate table can improve the performance of certain database queries.
2. Store different version metadata for different models.

Configuration

If you are using Postgres, you should also define the sequence that your custom version class will use:

class PostVersion < PaperTrail::Version
  self.table_name = :post_versions
  self.sequence_name = :post_versions_id_seq
end

If you only use custom version classes and don't have a versions table, you must let ActiveRecord know that the PaperTrail::Version class is an abstract_class.

# app/models/paper_trail/version.rb
module PaperTrail
  class Version < ActiveRecord::Base
    include PaperTrail::VersionConcern
    self.abstract_class = true
  end
end

You can also specify custom names for the versions and version associations. This is useful if you already have versions or/and version methods on your model. For example:

class Post < ActiveRecord::Base
  has_paper_trail :versions => :paper_trail_versions,
                  :version  => :paper_trail_version

  # Existing versions method.  We don't want to clash.
  def versions
    ...
  end
  # Existing version method.  We don't want to clash.
  def version
    ...
  end
end

Associations

Experimental Feature: Known Issues: #542, #590. See also: Caveats below.

PaperTrail can restore three types of associations: Has-One, Has-Many, and Has-Many-Through. In order to do this, you will need to create a version_associations table, either at installation time with the rails generate paper_trail:install --with-associations option or manually. PaperTrail will store in that table additional information to correlate versions of the association and versions of the model when the associated record is changed. When reifying the model, PaperTrail can use this table, together with the transaction_id to find the correct version of the association and reify it. The transaction_id is a unique id for version records created in the same transaction. It is used to associate the version of the model and the version of the association that are created in the same transaction.

To restore Has-One associations as they were at the time, pass option :has_one => true to reify. To restore Has-Many and Has-Many-Through associations, use option :has_many => true. For example:

class Location < ActiveRecord::Base
  belongs_to :treasure
  has_paper_trail
end

class Treasure < ActiveRecord::Base
  has_one :location
  has_paper_trail
end

treasure.amount                  # 100
treasure.location.latitude       # 12.345

treasure.update_attributes :amount => 153
treasure.location.update_attributes :latitude => 54.321

t = treasure.versions.last.reify(:has_one => true)
t.amount                         # 100
t.location.latitude              # 12.345

If the parent and child are updated in one go, PaperTrail can use the aforementioned transaction_id to reify the models as they were before the transaction (instead of before the update to the model).

treasure.amount                  # 100
treasure.location.latitude       # 12.345

Treasure.transaction do
treasure.location.update_attributes :latitude => 54.321
treasure.update_attributes :amount => 153
end

t = treasure.versions.last.reify(:has_one => true)
t.amount                         # 100
t.location.latitude              # 12.345, instead of 54.321

By default, PaperTrail excludes an associated record from the reified parent model if the associated record exists in the live model but did not exist as at the time the version was created. This is usually what you want if you just want to look at the reified version. But if you want to persist it, it would be better to pass in option :mark_for_destruction => true so that the associated record is included and marked for destruction. Note that mark_for_destruction only has an effect on associations marked with autosave: true.

class Widget < ActiveRecord::Base
  has_paper_trail
  has_one :wotsit, autosave: true
end

class Wotsit < ActiveRecord::Base
  has_paper_trail
  belongs_to :widget
end

widget = Widget.create(:name => 'widget_0')
widget.update_attributes(:name => 'widget_1')
widget.create_wotsit(:name => 'wotsit')

widget_0 = widget.versions.last.reify(:has_one => true)
widget_0.wotsit                                  # nil

widget_0 = widget.versions.last.reify(:has_one => true, :mark_for_destruction => true)
widget_0.wotsit.marked_for_destruction?          # true
widget_0.save!
widget.reload.wotsit                             # nil

Caveats:

1. PaperTrail can't restore an association properly if the association record can be updated to replace its parent model (by replacing the foreign key)
2. Currently PaperTrail only support single version_associations table. The implication is that you can only use a single table to store the versions for all related models. Sorry for those who use multiple version tables.
3. PaperTrail only reifies the first level of associations, i.e., it does not reify any associations of its associations, and so on.
4. PaperTrail relies on the callbacks on the association model (and the :through association model for Has-Many-Through associations) to record the versions and the relationship between the versions. If the association is changed without invoking the callbacks, Reification won't work. Below are some examples:

Given these models:

class Book < ActiveRecord::Base
  has_many :authorships, :dependent => :destroy
  has_many :authors, :through => :authorships, :source => :person
  has_paper_trail
end

class Authorship < ActiveRecord::Base
  belongs_to :book
  belongs_to :person
  has_paper_trail      # NOTE
end

class Person < ActiveRecord::Base
  has_many :authorships, :dependent => :destroy
  has_many :books, :through => :authorships
  has_paper_trail
end

Then each of the following will store authorship versions:

@book.authors << @dostoyevsky
@book.authors.create :name => 'Tolstoy'
@book.authorships.last.destroy
@book.authorships.clear
@book.author_ids = [@solzhenistyn.id, @dostoyevsky.id]

But none of these will:

@book.authors.delete @tolstoy
@book.author_ids = []
@book.authors = []

Having said that, you can apparently get all these working (I haven't tested it myself) with this patch:

# In config/initializers/active_record_patch.rb
module ActiveRecord
  # = Active Record Has Many Through Association
  module Associations
    class HasManyThroughAssociation < HasManyAssociation #:nodoc:
      alias_method :original_delete_records, :delete_records

      def delete_records(records, method)
        method ||= :destroy
        original_delete_records(records, method)
      end
    end
  end
end

See issue 113 for a discussion about this.

Storing Metadata

You can store arbitrary model-level metadata alongside each version like this:

class Article < ActiveRecord::Base
  belongs_to :author
  has_paper_trail :meta => { :author_id  => :author_id,
                             :word_count => :count_words,
                             :answer     => 42 }
  def count_words
    153
  end
end

PaperTrail will call your proc with the current article and store the result in the author_id column of the versions table.

Advantages of Metadata

Why would you do this? In this example, author_id is an attribute of Article and PaperTrail will store it anyway in a serialized form in the object column of the version record. But let's say you wanted to pull out all versions for a particular author; without the metadata you would have to deserialize (reify) each version object to see if belonged to the author in question. Clearly this is inefficient. Using the metadata you can find just those versions you want:

PaperTrail::Version.where(:author_id => author_id)

Metadata from Controllers

You can also store any information you like from your controller. Override the info_for_paper_trail method in your controller to return a hash whose keys correspond to columns in your versions table.

class ApplicationController
  def info_for_paper_trail
    { :ip => request.remote_ip, :user_agent => request.user_agent }
  end
end

Protected Attributes and Metadata

If you are using rails 3 or the protected_attributes gem you must declare your metadata columns to be attr_accessible.

# app/models/paper_trail/version.rb
module PaperTrail
  class Version < ActiveRecord::Base
    include PaperTrail::VersionConcern
    attr_accessible :author_id, :word_count, :answer
  end
end

If you're using strong_parameters instead of protected_attributes then there is no need to use attr_accessible.

Using a custom serializer

By default, PaperTrail stores your changes as a YAML dump. You can override this with the serializer config option:

PaperTrail.serializer = MyCustomSerializer

A valid serializer is a module (or class) that defines a load and dump method. These serializers are included in the gem for your convenience:

• PaperTrail::Serializers::YAML - Default
• PaperTrail::Serializers::JSON

PostgreSQL JSON column type support

If you use PostgreSQL, and would like to store your object (and/or object_changes) data in a column of type JSON or type JSONB, specify json instead of text for these columns in your migration:

create_table :versions do |t|
  ...
  t.json :object          # Full object changes
  t.json :object_changes  # Optional column-level changes
  ...
end

Note: You don't need to use a particular serializer for the PostgreSQL JSON column type.

Convert a column from text to json

Postgres' alter column command will not automatically convert a text column to json, but it can still be done with plain SQL.

alter table versions
alter column object type json
using object::json;

SerializedAttributes support

PaperTrail has a config option that can be used to enable/disable whether PaperTrail attempts to utilize ActiveRecord's serialized_attributes feature. Note: This is enabled by default when PaperTrail is used with ActiveRecord version < 4.2, and disabled by default when used with ActiveRecord 4.2.x. Since serialized_attributes will be removed in ActiveRecord version 5.0, this configuration value has no functionality when PaperTrail is used with version 5.0 or greater.

# Enable support
PaperTrail.config.serialized_attributes = true
# Disable support
PaperTrail.config.serialized_attributes = false
# Get current setting
PaperTrail.serialized_attributes?

Testing

You may want to turn PaperTrail off to speed up your tests. See the Turning PaperTrail Off/On section above for tips on usage with Test::Unit.

RSpec

PaperTrail provides a helper that works with RSpec to make it easier to control when PaperTrail is enabled during testing.

If you wish to use the helper, you will need to require it in your RSpec test helper like so:

# spec/rails_helper.rb

ENV["RAILS_ENV"] ||= 'test'
require 'spec_helper'
require File.expand_path("../../config/environment", __FILE__)
require 'rspec/rails'
...
require 'paper_trail/frameworks/rspec'

When the helper is loaded, PaperTrail will be turned off for all tests by default. When you wish to enable PaperTrail for a test you can either wrap the test in a with_versioning block, or pass in :versioning => true option to a spec block, like so:

describe "RSpec test group" do
  it 'by default, PaperTrail will be turned off' do
    expect(PaperTrail).to_not be_enabled
  end

  with_versioning do
    it 'within a `with_versioning` block it will be turned on' do
      expect(PaperTrail).to be_enabled
    end
  end

  it 'can be turned on at the `it` or `describe` level like this', :versioning => true do
    expect(PaperTrail).to be_enabled
  end
end

The helper will also reset the PaperTrail.whodunnit value to nil before each test to help prevent data spillover between tests. If you are using PaperTrail with Rails, the helper will automatically set the PaperTrail.controller_info value to {} as well, again, to help prevent data spillover between tests.

There is also a be_versioned matcher provided by PaperTrail's RSpec helper which can be leveraged like so:

class Widget < ActiveRecord::Base
end

describe Widget do
  it "is not versioned by default" do
    is_expected.to_not be_versioned
  end

  describe "add versioning to the `Widget` class" do
    before(:all) do
      class Widget < ActiveRecord::Base
        has_paper_trail
      end
    end

    it "enables paper trail" do
      is_expected.to be_versioned
    end
  end
end

It is also possible to do assertions on the versions using have_a_version_with matcher

 describe '`have_a_version_with` matcher' do
    before do
      widget.update_attributes!(:name => 'Leonard', :an_integer => 1 )
      widget.update_attributes!(:name => 'Tom')
      widget.update_attributes!(:name => 'Bob')
    end

    it "is possible to do assertions on versions" do
       expect(widget).to have_a_version_with :name => 'Leonard', :an_integer => 1
       expect(widget).to have_a_version_with :an_integer => 1
       expect(widget).to have_a_version_with :name => 'Tom'
    end
  end

Cucumber

PaperTrail provides a helper for Cucumber that works similar to the RSpec helper.If you wish to use the helper, you will need to require in your cucumber helper like so:

# features/support/env.rb

ENV["RAILS_ENV"] ||= "cucumber"
require File.expand_path(File.dirname(__FILE__) + '/../../config/environment')
...
require 'paper_trail/frameworks/cucumber'

When the helper is loaded, PaperTrail will be turned off for all scenarios by a before hook added by the helper by default. When you wish to enable PaperTrail for a scenario, you can wrap code in a with_versioning block in a step, like so:

Given /I want versioning on my model/ do
  with_versioning do
    # PaperTrail will be turned on for all code inside of this block
  end
end

The helper will also reset the PaperTrail.whodunnit value to nil before each test to help prevent data spillover between tests. If you are using PaperTrail with Rails, the helper will automatically set the PaperTrail.controller_info value to {} as well, again, to help prevent data spillover between tests.

Spork

If you wish to use the RSpec or Cucumber helpers with Spork, you will need to manually require the helper(s) in your prefork block on your test helper, like so:

# spec/rails_helper.rb

require 'spork'

Spork.prefork do
  # This file is copied to spec/ when you run 'rails generate rspec:install'
  ENV["RAILS_ENV"] ||= 'test'
  require 'spec_helper'
  require File.expand_path("../../config/environment", __FILE__)
  require 'rspec/rails'
  require 'paper_trail/frameworks/rspec'
  require 'paper_trail/frameworks/cucumber'
  ...
end

Zeus or Spring

If you wish to use the RSpec or Cucumber helpers with Zeus or Spring, you will need to manually require the helper(s) in your test helper, like so:

# spec/rails_helper.rb

ENV["RAILS_ENV"] ||= 'test'
require 'spec_helper'
require File.expand_path("../../config/environment", __FILE__)
require 'rspec/rails'
require 'paper_trail/frameworks/rspec'

Testing PaperTrail

Paper Trail has facilities to test against Postgres, Mysql and SQLite. To switch between DB engines you will need to export the DB variable for the engine you wish to test aganist.

Though be aware we do not have the abilty to create the db's (except sqlite) for you. You can look at .travis.yml before_script for an example of how to create the db's needed.

export DB=postgres
export DB=mysql
export DB=sqlite # this is default

Articles

• Jutsu #8 - Version your RoR models with PaperTrail, Thibault, 29th September 2014
• Versioning with PaperTrail, Ilya Bodrov, 10th April 2014
• Using PaperTrail to track stack traces, T James Corcoran's blog, 1st October 2013.
• RailsCast #255 - Undo with Paper Trail, Feb 28, 2011
• RailsCast #255 - Undo with PaperTrail, 28th February 2011.
• Keep a Paper Trail with PaperTrail, Linux Magazine, 16th September 2009.

Problems

Please use GitHub's issue tracker.

Contributors

Many thanks to:

• Dmitry Polushkin
• Russell Osborne
• Zachery Hostens
• Jeremy Weiskotten
• Phan Le
• jdrucza
• conickal
• Thibaud Guillaume-Gentil
• Danny Trelogan
• Mikl Kurkov
• Franco Catena
• Emmanuel Gomez
• Matthew MacLeod
• benzittlau
• Tom Derks
• Jonas Hoglund
• Stefan Huber
• thinkcast
• Dominik Sander
• Burke Libbey
• 6twenty
• nir0
• Eduard Tsech
• Mathieu Arnold
• Nicholas Thrower
• Benjamin Curtis
• Peter Harkins
• Mohd Amree
• Nikita Cernovs
• Jason Noble
• Jared Mehle
• Eric Schwartz
• Ben Woosley
• Philip Arndt
• Daniel Vydra
• Byron Bowerman
• Nicolas Buduroi
• Pikender Sharma
• Paul Brannan
• Ben Morrall
• Yves Senn
• Ben Atkins
• Tyler Rick
• Bradley Priest
• David Butler
• Paul Belt
• Vlad Bokov
• Sean Marcia
• Chulki Lee
• Lucas Souza
• Russell Osborne
• Ben Li
• Felix Liu

Inspirations

• Simply Versioned
• Acts As Audited

Intellectual Property

Copyright (c) 2011 Andy Stewart (boss@airbladesoftware.com). Released under the MIT licence.