PaperTrail-AssociationTracking

Plugin for the PaperTrail gem to track and reify associations. This gem was extracted from PaperTrail for v9.2.0 to simplify things in PaperTrail and association tracking separately.

PR's will happily be accepted

PaperTrail-AssociationTracking can restore three types of associations: Has-One, Has-Many, and Has-Many-Through.

It will store in the version_associations table additional information to correlate versions of the association and versions of the model when the associated record is changed. When reifying the model, it will utilize 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.

Table of Contents

• Install
• Usage
• Limitations
• Known Issues
• Contributing
• Credits
• Alternative Solution

Install

gem 'paper_trail'
gem 'paper_trail-association_tracking'

Then run rails generate paper_trail_association_tracking:install which will do the following two things for you:

1. Create a version_associations table
2. Set PaperTrail.config.track_associations = true in an initializer

Usage

First, ensure that you have added has_paper_trail to your main model and all associated models that are to be tracked.

To restore associations as they were at the time you must pass any of the following options to the reify method.

• To restore Has-Many and Has-Many-Through associations, use option has_many: true
• To restore Has-One associations , use option has_one: true to reify
• To restore Belongs-To associations, use option belongs_to: true

For example:

item.versions.last.reify(has_many: true, has_one: true, belongs_to: false)

If you want the reified associations to be saved upon calling save on the parent model then you must set autosave: true on all required associations. A little tip, accepts_nested_attributes automatically sets autosave to true but you should probably still state it explicitly.

For example:

class Product
  has_many :photos, autosave: true
end

product = Product.first.versions.last.reify(has_many: true, has_one: true, belongs_to: false)
product.save! ### now this will also save all reified photos

If you do not set autosave: true true on the association then you will have to save/delete them manually.

For example:

class Product < ActiveRecord::Base
  has_paper_trail
  has_many :photos, autosave: false ### or if autosave not set
end

product = Product.create(name: 'product_0')
product.photos.create(name: 'photo')
product.update(name: 'product_a')
product.photos.create(name: 'photo')

reified_product = product.versions.last.reify(has_many: true, mark_for_destruction: true)
reified_product.save!
reified_product.name # product_a
reified_product.photos.size # 2
reified_product.photos.reload
reified_product.photos.size # 1 ### bad, didnt save the associations

product = Product.create(name: 'product_1')
product.update(name: 'product_b')
product.photos.create(name: 'photo')

reified_product = product.versions.last.reify(has_many: true, mark_for_destruction: true)
reified_product.save!
reified_product.name # product_b
reified_product.photos.size # 1
reified_product.photos.each{|x| x.marked_for_destruction? ? x.destroy! : x.save! }
reified_product.photos.size # 0

It will also respect AR transactions by utilizing the aforementioned transaction_id to reify the models as they were before the transaction (instead of before the update to the model).

For example:

item.amount                  # 100
item.location.latitude       # 12.345

Item.transaction do
  item.location.update(latitude: 54.321)
  item.update(amount: 153)
end

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

Limitations

1. Only reifies the first level of associations. If you want to include nested associations simply add :through relationships to your model.

2. Currently we only supports a single version_associations table. Therefore, you can only use a single table to store the versions for all related models.

3. 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, then reification won't work. Example:

   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
   
   ### Each of the following will store authorship versions:
   @book.authors << @john
   @book.authors.create(name: 'Jack')
   @book.authorships.last.destroy
   @book.authorships.clear
   @book.author_ids = [@john.id, @joe.id]
   
   ### But none of these will:
   @book.authors.delete @john
   @book.author_ids = []
   @book.authors = []

Known Issues

1. Sometimes the has_one association will find more than one possible candidate and will raise a PaperTrailAssociationTracking::Reifiers::HasOne::FoundMoreThanOne error. For example, see spec/models/person_spec.rb
   • If you are not using STI, you may want to just assume the first result of multiple is the correct one and continue. PaperTrail <= v8 did this without error or warning. To do so add the following line to your initializer: PaperTrail.config.association_reify_error_behaviour = :warn. Valid options are: [:error, :warn, :ignore]
   • When using STI, even if you enable :warn you will likely still end up recieving an ActiveRecord::AssociationTypeMismatch error. See PT Issue #594. I strongly recommend that you do not use STI, however if you do need to decide to use STI, please see https://github.com/paper-trail-gem/paper_trail#4b1-the-optional-item_subtype-column
2. Not compatible with transactional tests, see PT Issue #542. However, apparently there has been some success by using the transactional_capybara gem.

Contributing

We use the appraisal gem for testing multiple versions of paper_trail and activerecord. Please use the following steps to test using appraisal.

1. bundle exec appraisal install
2. bundle exec appraisal rake test

Credits

Maintained by Weston Ganger - @westonganger

Plugin authored by Weston Ganger - @westonganger

Associations code originally contributed by Ben Atkins, Jared Beck, Andy Stewart & more

Alternative Solution

Model Versioning and Restoration require concious thought, design, and understanding. You should understand your versioning and restoration process completely. Because PT-AT it is mostly a blackbox solution which encourages you to set it up and then assume its "Just Working". This can make for major data problems later.

Instead I recommend a newer gem that I have created for handling snapshots of records and associations called active_snapshot. This gem does not utilize paper_trail at all. The focus of this gem is to have a simple and fully understandable design is easy to customize and know inside and out for your projects needs.