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.

Documentation

This is the user guide. See also, the API reference.

Choose version: Unreleased, 15.1, 14.0, 13.0, 12.3, 11.1, 10.3, 9.2, 8.1, 7.1, 6.0, 5.2, 4.2, 3.0, 2.7, 1.6

1. Introduction
2. Limiting What is Versioned, and When
3. Working With Versions
4. Saving More Information About Versions
5. ActiveRecord
6. Extensibility
7. Testing
8. PaperTrail Plugins
9. Integration with Other Libraries
10. Related Libraries and Ports
Articles
Problems
Contributors
Contributing
Inspirations
Intellectual Property

1. Introduction

1.a. Compatibility

paper_trail	ruby	activerecord
unreleased	>= 3.0.0	>= 6.1, < 7.2
15	>= 3.0.0	>= 6.1, < 7.2
14	>= 2.7.0	>= 6.0, < 7.1
13	>= 2.6.0	>= 5.2, < 7.1
12	>= 2.6.0	>= 5.2, < 7.1
11	>= 2.4.0	>= 5.2, < 6.1
10	>= 2.3.0	>= 4.2, < 6.1
9	>= 2.3.0	>= 4.2, < 5.3
8	>= 2.2.0	>= 4.2, < 5.2
7	>= 2.1.0	>= 4.0, < 5.2
6	>= 1.9.3	>= 4.0, < 5.2
5	>= 1.9.3	>= 3.0, < 5.1
4	>= 1.8.7	>= 3.0, < 5.1
3	>= 1.8.7	>= 3.0, < 5
2	>= 1.8.7	>= 3.0, < 4
1	>= 1.8.7	>= 2.3, < 3

Experts: to install incompatible versions of activerecord, see paper_trail/compatibility.rb.

1.b. Installation

Add PaperTrail to your Gemfile and run bundle.

gem 'paper_trail'

Add a versions table to your database:

bundle exec rails generate paper_trail:install [--with-changes] [--uuid]
bundle exec rails db:migrate

See section 5.c. Generators for details.

Add has_paper_trail to the models you want to track.

class Widget < ActiveRecord::Base
  has_paper_trail
end

If your controllers have a current_user method, you can easily track who is responsible for changes by adding a controller callback.
```
class ApplicationController
  before_action :set_paper_trail_whodunnit
end
```

1.c. Basic Usage

Your models now have 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', 'create', 'destroy'. See also: "The versions.event Column"
v.created_at
v.whodunnit # ID of `current_user`. Requires `set_paper_trail_whodunnit` callback.
widget = v.reify # The widget as it was before the update (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 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 row. Most other auditing/versioning plugins store the After row.

1.d. API Summary

An introductory sample of common features.

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, but overriding this method is not supported.
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.paper_trail.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.paper_trail.version_at(timestamp)

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

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

And a PaperTrail::Version instance (which is just an ordinary ActiveRecord instance, with all the usual methods) has methods such as:

# 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

This is just a sample of common features. Keep reading for more.

1.e. Configuration

Many aspects of PaperTrail are configurable for individual models; typically this is achieved by passing options to the has_paper_trail method within a given model.

Some aspects of PaperTrail are configured globally for all models. These settings are assigned directly on the PaperTrail.config object. A common place to put these settings is in a Rails initializer file such as config/initializers/paper_trail.rb or in an environment-specific configuration file such as config/environments/test.rb.

1.e.1 Global

Global configuration options affect all threads.

association_reify_error_behaviour
enabled
has_paper_trail_defaults
object_changes_adapter
serializer
version_limit

Syntax example: (options described in detail later)

# config/initializers/paper_trail.rb
PaperTrail.config.enabled = true
PaperTrail.config.has_paper_trail_defaults = {
  on: %i[create update destroy]
}
PaperTrail.config.version_limit = 3

These options are intended to be set only once, during app initialization (eg. in config/initializers). It is unsafe to change them while the app is running. In contrast, PaperTrail.request has various options that only apply to a single HTTP request and thus are safe to use while the app is running.

2. Limiting What is Versioned, and When

2.a. Choosing Lifecycle Events To Monitor

You can choose which events to track with the on option. For example, if you only want to track update events:

class Article < ActiveRecord::Base
  has_paper_trail on: [:update]
end

has_paper_trail installs callbacks for the specified lifecycle events.

There are four potential callbacks, and the default is to install all four, ie. on: [:create, :destroy, :touch, :update].

The `versions.event` Column

Your versions table has an event column with three possible values:

event	callback
create	create
destroy	destroy
update	touch, update

You may also have the PaperTrail::Version model save a custom string in its event field instead of the typical create, update, destroy. PaperTrail adds an attr_accessor to your model named paper_trail_event, and will insert it, if present, in the event column.

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

Controlling the Order of AR Callbacks

If there are other callbacks in your model, their order relative to those installed by has_paper_trail may matter. If you need to control their order, use the paper_trail_on_* methods.

class Article < ActiveRecord::Base
  # Include PaperTrail, but do not install any callbacks. Passing the
  # empty array to `:on` omits callbacks.
  has_paper_trail on: []

  # Add callbacks in the order you need.
  paper_trail.on_destroy    # add destroy callback
  paper_trail.on_update     # etc.
  paper_trail.on_create
  paper_trail.on_touch
end

The paper_trail.on_destroy method can be further configured to happen :before or :after the destroy event. Until PaperTrail 4, the default was :after. Starting with PaperTrail 5, the default is :before, to support ActiveRecord 5. (see paper-trail-gem#683)

2.b. 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 Based on Changed Attributes

Starting with PaperTrail 4.0, versions are saved during an after-callback. If you decide whether to save a new version based on changed attributes, use attribute_name_was instead of attribute_name.

Saving a New Version Manually

You may want to save a new version regardless of options like :on, :if, or :unless. Or, in rare situations, you may want to save a new version even if the record has not changed.

my_model.paper_trail.save_with_version

2.c. Choosing Attributes To Monitor

Ignore

If you don't want a version created when only a certain attribute changes, you can ignore that attribute:

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

Changes to just the title or rating will not create a version record. Changes to other attributes will create a version record.

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

Note: ignored fields will be stored in the version records. If you want to keep a field out of the versions table, use :skip instead of :ignore; skipped fields are also implicitly ignored.

The :ignore option can also accept Hash arguments that we are considering deprecating.

class Article < ActiveRecord::Base
  has_paper_trail ignore: [:title, { color: proc { |obj| obj.color == "Yellow" } }]
end

Only

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

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

Only changes to the title will create a version record.

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

The :only option can also accept Hash arguments that we are considering deprecating.

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

If the title is not blank, then only changes to the title will create a version record.

a = Article.create
a.versions.length                         # 1
a.update content: 'Hello'
a.versions.length                         # 2
a.update title: 'Title One'
a.versions.length                         # 3
a.update content: 'Hai'
a.versions.length                         # 3
a.paper_trail.previous_version.content    # "Hello"
a.update title: 'Title Two'
a.versions.length                         # 4
a.paper_trail.previous_version.content    # "Hai"

Configuring both :ignore and :only is not recommended, but it should work as expected. 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.

Skip

If you never want a field's values in the versions table, you can :skip the attribute. As with :ignore, updates to these attributes will not create a version record. In addition, if a version record is created for some other reason, these attributes will not be persisted.

class Author < ActiveRecord::Base
  has_paper_trail skip: [:social_security_number]
end

Author's social security numbers will never appear in the versions log, and if an author updates only their social security number, it won't create a version record.

Comparing `:ignore`, `:only`, and `:skip`

:only is basically the same as :ignore, but its inverse.
:ignore controls whether paper_trail will create a version record or not.
:skip controls whether paper_trail will save that field with the version record.
Skipped fields are also implicitly ignored. paper_trail does this internally.
Ignored fields are not implicitly skipped.

So:

Ignore a field if you don't want a version record created when it's the only field to change.
Skip a field if you don't want it to be saved with any version records.

2.d. Turning PaperTrail Off

PaperTrail is on by default, but sometimes you don't want to record versions.

Per Process

Turn PaperTrail off for all threads in a ruby process.

PaperTrail.enabled = false

Do not use this in production unless you have a good understanding of threads vs. processes.

A legitimate use case is to speed up tests. See Testing below.

Per HTTP Request

PaperTrail.request(enabled: false) do
  # no versions created
end

or,

PaperTrail.request.enabled = false
# no versions created
PaperTrail.request.enabled = true

Per Class

In the rare case that you need to disable versioning for one model while keeping versioning enabled for other models, use:

PaperTrail.request.disable_model(Banana)
# changes to Banana model do not create versions,
# but eg. changes to Kiwi model do.
PaperTrail.request.enable_model(Banana)
PaperTrail.request.enabled_for_model?(Banana) # => true

This setting, as with all PaperTrail.request settings, affects only the current request, not all threads.

For this rare use case, there is no convenient way to pass a block.

In a Rails Controller Callback (Not Recommended)

PaperTrail installs a callback in your rails controllers. The installed callback will call paper_trail_enabled_for_controller, which you can override.

class ApplicationController < ActionController::Base
  def paper_trail_enabled_for_controller
    # Don't omit `super` without a good reason.
    super && request.user_agent != 'Disable User-Agent'
  end
end

Because you are unable to control the order of callback execution, this technique is not recommended, but is preserved for backwards compatibility.

It would be better to install your own callback and use PaperTrail.request.enabled= as you see fit.

Per Method (Removed)

The widget.paper_trail.without_versioning method was removed in v10, without an exact replacement. To disable versioning, use the Per Class or Per HTTP Request methods.

2.e. 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

2.e.1 Per-model limit

Models can override the global PaperTrail.config.version_limit setting.

Example:

# initializer
PaperTrail.config.version_limit = 10

# At most 10 versions
has_paper_trail

# At most 3 versions (2 updates, 1 create). Overrides global version_limit.
has_paper_trail limit: 2

# Infinite versions
has_paper_trail limit: nil

3. Working With Versions

3.a. Reverting And Undeleting A Model

PaperTrail makes reverting to a previous version easy:

widget = Widget.find 42
widget.update name: 'Blah blah'
# Time passes....
widget = widget.paper_trail.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.paper_trail.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 = Widget.new(id:42)    # creating a new object with the same id, re-establishes the link
versions = widget.versions    # versions ordered by versions.created_at, ascending
widget = versions.last.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.

3.b. 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.paper_trail.previous_version # => widget == live_widget.versions.last.reify
widget = widget.paper_trail.previous_version      # => widget == live_widget.versions[-2].reify
widget = widget.paper_trail.next_version          # => widget == live_widget.versions.last.reify
widget.paper_trail.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 = version.previous
next_version = 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.paper_trail.live?            # true
widget = widget.paper_trail.previous_version
widget.paper_trail.live?            # false

3.c. 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 column to your versions table, PaperTrail will store the changes diff in each version. Ignored attributes are omitted.

widget = Widget.create name: 'Bob'
widget.versions.last.changeset # reads object_changes column
# {
#   "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 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
# {}

Prior to 10.0.0, the object_changes were only stored for create and update events. As of 10.0.0, they are stored for all three events.

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. -Andy

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.

Unfortunately, there is no currently widely available and supported library for diffing two ActiveRecord objects.

3.d. 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.where('created_at < ?', 1.day.ago).delete_all

3.e. Queries

You can query records in the versions table based on their object or object_changes columns.

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

# Find versions before and after attribute `atr` had value `v`:
PaperTrail::Version.where_object_changes(atr: 'v')

3.f. Defunct `item_id`s

The item_ids in your versions table can become defunct over time, potentially causing application errors when ids in the foreign table are reused. id reuse can be an explicit choice of the application, or implicitly caused by sequence cycling. The chance of id reuse is reduced (but not eliminated) with bigint ids or uuids, no cycle sequences, and/or when versions are periodically deleted.

Ideally, a Foreign Key Constraint (FKC) would set item_id to null when an item is deleted. However, items is a polymorphic relationship. A partial FKC (e.g. an FKC with a where clause) is possible, but only in Postgres, and it is impractical to maintain FKCs for every versioned table unless the number of such tables is very small.

If per-table Version classes are used, then a partial FKC is no longer needed. So, a normal FKC can be written in any RDBMS, but it remains impractical to maintain so many FKCs.

Some applications choose to handle this problem by "soft-deleting" versioned records, i.e. marking them as deleted instead of actually deleting them. This completely prevents id reuse, but adds complexity to the application. In most applications, this is the only known practical solution to the id reuse problem.

4. Saving More Information About Versions

4.a. Finding Out Who Was Responsible For A Change

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

PaperTrail.request.whodunnit = 'Andy Stewart'
widget.update name: 'Wibble'
widget.versions.last.whodunnit # Andy Stewart

Setting `whodunnit` to a `Proc`

whodunnit= also accepts a Proc, in the rare case that lazy evaluation is required.

PaperTrail.request.whodunnit = proc do
  caller.find { |c| c.starts_with? Rails.root.to_s }
end

Because lazy evaluation can be hard to troubleshoot, this is not recommended for common use.

Setting `whodunnit` Temporarily

To set whodunnit temporarily, for the duration of a block, use PaperTrail.request:

PaperTrail.request(whodunnit: 'Dorian Marié') do
  widget.update name: 'Wibble'
end

Setting `whodunnit` with a controller callback

If your controller has a current_user method, PaperTrail provides a callback that will assign current_user.id to whodunnit.

class ApplicationController
  before_action :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

Terminator and Originator

A version's whodunnit column tells us 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 tells us 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.request.whodunnit = 'Alice'
widget.update name: 'Yankee'
widget.paper_trail.originator               # 'Alice'
PaperTrail.request.whodunnit = 'Bob'
widget.update 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'

Storing an ActiveRecord globalid in whodunnit

If you would like whodunnit to return an ActiveRecord object instead of a string, please try the paper_trail-globalid gem.

4.b. Associations

To track and reify associations, use paper_trail-association_tracking (PT-AT).

From 2014 to 2018, association tracking was an experimental feature, but many issues were discovered. To attract new volunteers to address these issues, PT-AT was extracted (see paper-trail-gem#1070).

Even though it had always been an experimental feature, we didn't want the extraction of PT-AT to be a breaking change, so great care was taken to remove it slowly.

In PT 9, PT-AT was kept as a runtime dependency.
In PT 10, it became a development dependency (If you use it you must add it to your own Gemfile) and we kept running all of its tests.
In PT 11, it will no longer be a development dependency, and it is responsible for its own tests.

4.b.1 The optional `item_subtype` column

As of PT 10, users may add an item_subtype column to their versions table. When storing versions for STI models, rails stores the base class in item_type (that's just how polymorphic associations like item work) In addition, PT will now store the subclass in item_subtype. If this column is present PT-AT will use it to fix a rare issue with reification of STI subclasses.

add_column :versions, :item_subtype, :string, null: true

So, if you use PT-AT and STI, the addition of this column is recommended.

4.c. Storing Metadata

You can add your own custom columns to your versions table. Values can be given using Model Metadata or Controller Metadata.

Model Metadata

You can specify metadata in the model using has_paper_trail(meta:).

class Article < ActiveRecord::Base
  belongs_to :author
  has_paper_trail(
    meta: {
      author_id: :author_id, # model attribute
      word_count: :count_words, # arbitrary model method
      answer: 42, # scalar value
      editor: proc { |article| article.editor.full_name } # a Proc
    }
  )
  def count_words
    153
  end
end

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

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 can Override PaperTrail Columns

Experts only. Metadata will override the normal values that PT would have inserted into its own columns.

PT Column	How bad of an idea?	Alternative
created_at	forbidden*
event	meh	paper_trail_event
id	forbidden
item_id	forbidden
item_subtype	forbidden
item_type	forbidden
object	a little dangerous
object_changes	a little dangerous
updated_at	forbidden
whodunnit	meh	PaperTrail.request.whodunnit=

* forbidden - raises a PaperTrail::InvalidOption error as of PT 14

5. ActiveRecord

5.a. Single Table Inheritance (STI)

PaperTrail supports Single Table Inheritance, and even supports an un-versioned base model, as of 23ffbdc7e1.

class Fruit < ActiveRecord::Base
  # un-versioned base model
end
class Banana < Fruit
  has_paper_trail
end

However, there is a known issue when reifying associations, see paper-trail-gem#594

5.b. Configuring the `versions` Association

5.b.1. `versions` association

You may configure the name of the versions association by passing a different name (default is :versions) in the versions: options hash:

class Post < ActiveRecord::Base
  has_paper_trail versions: {
    name: :drafts
  }
end

Post.new.versions # => NoMethodError

You may pass a scope to the versions association with the scope: option:

class Post < ActiveRecord::Base
  has_paper_trail versions: {
    scope: -> { order("id desc") }
  }

  # Equivalent to:
  has_many :versions,
    -> { order("id desc") },
    class_name: 'PaperTrail::Version',
    as: :item
end

Any other options supported by has_many can be passed along to the has_many macro via the versions: options hash.

class Post < ActiveRecord::Base
  has_paper_trail versions: {
    extend: VersionsExtensions,
    autosave: false
  }
end

Overriding (instead of configuring) the versions method is not supported. Overriding associations is not recommended in general.

5.b.2. `item` association

A PaperTrail::Version object belongs_to an item, the relevant record.

The item association is first defined in PaperTrail::VersionConcern, but associations can be redefined.

Example: adding a `counter_cache` to `item` association

# app/models/paper_trail/version.rb
module PaperTrail
  class Version < ActiveRecord::Base
    belongs_to :item, polymorphic: true, counter_cache: true
  end
end

When redefining an association, its options are replaced not merged, so don't forget to specify the options from PaperTrail::VersionConcern, like polymorphic.

Be advised that redefining an association is an undocumented feature of Rails.

5.c. Generators

PaperTrail has one generator, paper_trail:install. It writes, but does not run, a migration file. The migration creates the versions table.

Reference

The most up-to-date documentation for this generator can be found by running rails generate paper_trail:install --help, but a copy is included here for convenience.

Usage:
  rails generate paper_trail:install [options]

Options:
  [--with-changes], [--no-with-changes]            # Store changeset (diff) with each version
  [--uuid]                                         # To use paper_trail with projects using uuid for id

Runtime options:
  -f, [--force]                    # Overwrite files that already exist
  -p, [--pretend], [--no-pretend]  # Run but do not make any changes
  -q, [--quiet], [--no-quiet]      # Suppress status output
  -s, [--skip], [--no-skip]        # Skip files that already exist

Generates (but does not run) a migration to add a versions table.

5.d. Protected Attributes

As of version 6, PT no longer supports rails 3 or the protected_attributes gem. If you are still using them, you may use PT 5 or lower. We recommend upgrading to strong_parameters as soon as possible.

If you must use protected_attributes for now, and want to use PT > 5, you can reopen PaperTrail::Version and add the following attr_accessible fields:

# app/models/paper_trail/version.rb
module PaperTrail
  class Version < ActiveRecord::Base
    include PaperTrail::VersionConcern
    attr_accessible :item_type, :item_id, :event, :whodunnit, :object, :object_changes, :created_at
  end
end

This unsupported workaround has been tested with protected_attributes 1.0.9 / rails 4.2.8 / paper_trail 7.0.3.

6. Extensibility

6.a. 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 versions: {
    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

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.
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 your base version class (eg. ApplicationVersion below) class is an abstract_class.

# app/models/application_version.rb
class ApplicationVersion < ActiveRecord::Base
  include PaperTrail::VersionConcern
  self.abstract_class = true
end

class PostVersion < ApplicationVersion
  self.table_name = :post_versions
  self.sequence_name = :post_versions_id_seq
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: { name: :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

6.b. 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

If you use the PostgreSQL json or jsonb column type, you do not need to specify a PaperTrail.serializer.

Convert existing YAML data to JSON

If you've been using PaperTrail for a while with the default YAML serializer and you want to switch to JSON or JSONB, you're in a bit of a bind because there's no automatic way to migrate your data. The first (slow) option is to loop over every record and parse it in Ruby, then write to a temporary column:

add_column :versions, :new_object, :jsonb # or :json
# add_column :versions, :new_object_changes, :jsonb # or :json

# PaperTrail::Version.reset_column_information # needed for rails < 6

PaperTrail::Version.where.not(object: nil).find_each do |version|
  version.update_column(:new_object, YAML.load(version.object))

  # if version.object_changes
  #   version.update_column(
  #     :new_object_changes,
  #     YAML.load(version.object_changes)
  #   )
  # end
end

remove_column :versions, :object
# remove_column :versions, :object_changes
rename_column :versions, :new_object, :object
# rename_column :versions, :new_object_changes, :object_changes

This technique can be very slow if you have a lot of data. Though slow, it is safe in databases where transactions are protected against DDL, such as Postgres. In databases without such protection, such as MySQL, a table lock may be necessary.

If the above technique is too slow for your needs, and you're okay doing without PaperTrail data temporarily, you can create the new column without converting the data.

rename_column :versions, :object, :old_object
add_column :versions, :object, :jsonb # or :json

After that migration, your historical data still exists as YAML, and new data will be stored as JSON. Next, convert records from YAML to JSON using a background script.

PaperTrail::Version.where.not(old_object: nil).find_each do |version|
  version.update_columns old_object: nil, object: YAML.load(version.old_object)
end

Finally, in another migration, remove the old column.

remove_column :versions, :old_object

If you use the optional object_changes column, don't forget to convert it also, using the same technique.

Convert a Column from Text to JSON

If your object column already contains JSON data, and you want to change its data type to json or jsonb, you can use the following DDL. Of course, if your object column contains YAML, you must first convert the data to JSON (see above) before you can change the column type.

Using SQL:

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

Using ActiveRecord:

class ConvertVersionsObjectToJson < ActiveRecord::Migration
  def up
    change_column :versions, :object, 'jsonb USING object::jsonb'
  end

  def down
    change_column :versions, :object, 'text USING object::text'
  end
end

6.c. Custom Object Changes

To fully control the contents of their object_changes column, expert users can write an adapter.

PaperTrail.config.object_changes_adapter = MyObjectChangesAdapter.new

class MyObjectChangesAdapter
  # @param changes Hash
  # @return Hash
  def diff(changes)
    # ...
  end
end

You should only use this feature if you are comfortable reading PT's source to see exactly how the adapter is used. For example, see how diff is used by reading ::PaperTrail::Events::Base#recordable_object_changes.

An adapter can implement any or all of the following methods:

diff: Returns the changeset in the desired format given the changeset in the original format
load_changeset: Returns the changeset for a given version object
where_object_changes: Returns the records resulting from the given hash of attributes.
where_object_changes_from: Returns the records resulting from the given hash of attributes where the attributes changed from the provided value(s).
where_object_changes_to: Returns the records resulting from the given hash of attributes where the attributes changed to the provided value(s).
where_attribute_changes: Returns the records where the attribute changed to or from any value.

Depending on your needs, you may choose to implement only a subset of these methods.

Known Adapters

paper_trail-hashdiff

6.d. Excluding the Object Column

The object column ends up storing a lot of duplicate data if you have models that have many columns, and that are updated many times. You can save ~50% of storage space by removing the column from the versions table. It's important to note that this will disable reify and where_object.

7. Testing

You may want to turn PaperTrail off to speed up your tests. See Turning PaperTrail Off above.

7.a. Minitest

First, disable PT for the entire ruby process.

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

Then, to enable PT for specific tests, you can add a with_versioning test helper method.

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

Then, use the helper in your tests.

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

7.b. RSpec

PaperTrail provides a helper, paper_trail/frameworks/rspec.rb, that works with RSpec to make it easier to control when PaperTrail is enabled during testing.

# 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'

With the helper loaded, PaperTrail will be turned off for all tests by default. 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.

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', versioning: true do
    expect(PaperTrail).to be_enabled
  end
end

The helper will also reset whodunnit 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.request.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

Matchers

The have_a_version_with matcher makes assertions about versions using where_object, based on the object column.

describe '`have_a_version_with` matcher' do
  it 'is possible to do assertions on version attributes' do
    widget.update!(name: 'Leonard', an_integer: 1)
    widget.update!(name: 'Tom')
    widget.update!(name: 'Bob')
    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

The have_a_version_with_changes matcher makes assertions about versions using where_object_changes, based on the optional object_changes column.

describe '`have_a_version_with_changes` matcher' do
  it 'is possible to do assertions on version changes' do
    widget.update!(name: 'Leonard', an_integer: 1)
    widget.update!(name: 'Tom')
    widget.update!(name: 'Bob')
    expect(widget).to have_a_version_with_changes name: 'Leonard', an_integer: 2
    expect(widget).to have_a_version_with_changes an_integer: 2
    expect(widget).to have_a_version_with_changes name: 'Bob'
  end
end

For more examples of the RSpec matchers, see the Widget spec

7.c. Cucumber

PaperTrail provides a helper for Cucumber that works similar to the RSpec helper. If you want 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 want 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 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.request.controller_info value to {} as well, again, to help prevent data spillover between tests.

7.d. Spork

If you want 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

7.e. Zeus or Spring

If you want 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'

8. PaperTrail Plugins

paper_trail-active_record
paper_trail-association_tracking - track and reify associations
paper_trail-audit
paper_trail-background
paper_trail-globalid - enhances whodunnit by adding an actor
paper_trail-hashdiff
paper_trail-rails
paper_trail-related_changes
paper_trail-sinatra
paper_trail_actor
paper_trail_changes
paper_trail_manager
paper_trail_scrapbook
paper_trail_ui
revertible_paper_trail
rspec-paper_trail
sequel_paper_trail

9. Integration with Other Libraries

ActiveAdmin
paper_trail_manager - Browse, subscribe, view and revert changes to records with rails and paper_trail
rails_admin_history_rollback - History rollback for rails_admin with PT
Sinatra - paper_trail-sinatra
globalize - globalize-versioning
solidus_papertrail - PT integration for Solidus method to instances of PaperTrail::Version that returns the ActiveRecord object who was responsible for change

10. Related Libraries and Ports

izelnakri/paper_trail - An Ecto library, inspired by PT.
sequelize-paper-trail - A JS library, inspired by PT. A sequelize plugin for tracking revision history of model instances.

Articles

PaperTrail Gem Tutorial, 20th April 2020.
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 PaperTrail, 28th February 2011.
Keep a Paper Trail with PaperTrail, Linux Magazine, 16th September 2009.

Problems

Please use GitHub's issue tracker.

Contributors

Created by Andy Stewart in 2010, maintained since 2012 by Ben Atkins, since 2015 by Jared Beck, with contributions by over 150 people.

t27duck/paper_trail