Plugins - acts_as_soft_deletable - Agile Web Development

Plugins - acts_as_soft_deletable

This plugin provides the ability to soft delete ActiveRecord models. When models are destroyed, they will be archived into a special deleted table. They can later be restored easily.

    class Artist < ActiveRecord::Base
      acts_as_soft_deletable # This will wrap the destroy method to provide soft delete
                             # support and create a new ActiveRecord class called Artist::Deleted
    end

    model = Artist.find(34)
    model.destroy   # removes row from artists table, and adds a row to
                    # deleted_artists table

    deleted = Artist::Deleted.find(34)
    deleted.undestroy!  # adds the row back to the artists table, and removes
                        # if from the deleted_artists table

    restored = Artist.find(34) # The artist is restored with all the same
                               # information. The updated_at column will be
                               # Time.now if it exists.
  end

Compare to acts_as_paranoid

Acts_as_paranoid takes the approach of using a deleted_at flag in the models table. If the deleted_at column has a value, the row is considered ‘deleted’. The problem with this approach is that all finds on the model have to exclude ‘deleted’ rows. This turns out be be a challenge. Acts_as_paranoid patches the ActiveRecord internals to accomplish this, but it is fragile and could break with future changes to ActiveRecord. Also, some of the more exotic finds currently don’t work (has_many :through with polymorphism as of March 2008) and supporting them means running on an upgrade treadmill to keep up with the evolution of ActiveRecord.

This plugin avoids these problems by allowing the row to be deleted and archiving it into another table. The behavior of ActiveRecord::Base#Find doesn’t have to change which should mean that this plugin is more immune to breaking due to ActiveRecord development. The tradeoff is that the deleted table needs to be maintained along with the source table. For example, if the artists table adds a column in a future migration, then the deleted_artists table needs that column as well.

A migration helper is available (see below) that will help keep the deleted table in sync. Also, a unit test helper is provided (again, see below) which adds unit tests to the model ensuring soft delete is working. If this is used, the test will fail if the deleted table gets out of sync.

Setup

Model

Any ActiveRecord class that wants the soft delete functionality should add the following line to their class definition:

  class SomeModel < ActiveRecord::Base
    acts_as_soft_deletable
    ...

Migration

and setup the deleted table with the following migration:

  class AddActsAsSoftDeletable < ActiveRecord::Migration
    def self.up
      SomeModel::Deleted.create_table
    end

    def self.down
      SomeModel::Deleted.drop_table
    end
  end

Any changes to the original table (such as adding a column) should be reflected in the deleted table. Use the update_columns method:

  class AddSkuColumn < ActiveRecord::Migration
    def self.up
      add_column 'items', 'sku', :string
      Item::Deleted.update_columns # will add sku column
    end

    def self.down
      remove_column 'items', 'sku'
      Item::Deleted.update_columns # will remove sku column
    end
  end

Note that update_columns will happily delete columns if asked which will lose data forever. I’m not sure if this behavior is fine or horrifying, but it’s definitely something to keep in mind. I’d appreciate feedback on this.

Unit tests

A model’s soft delete capabilities can be easily unit tested by using this provided assert:

  def test_soft_delete_works
    # will run the model through a destroy and undestroy while making sure all values were saved
    assert_model_soft_deletes( items(:radar_detector) )
  end

This was developed with Test::Unit in mind. Not sure how well it works with rspec.

Thanks

Substantial, my employer for letting me release this, acts_as_paranoid and technoweenie, for a plugin I’ve got good years of use out of, and acts_as_versioned, who’s approach influenced this plugin.