Merge pull request #849 from DFE-Digital/1173-data-versioning

Add data versioning.

Gemfile

@@ -27,6 +27,7 @@ gem "omniauth", "~> 2.1"
 gem "omniauth-oauth2", "~> 1.8"
 gem "omniauth-rails_csrf_protection"
 gem "pagy"
+gem "paper_trail", "~> 14.0"
 gem "pg", ">= 0.18", "< 2.0"
 gem "pg_search"
 gem "puma", "~> 6.3"

Gemfile.lock

@@ -293,6 +293,9 @@ GEM
       omniauth (~> 2.0)
     orm_adapter (0.5.0)
     pagy (6.0.4)
+    paper_trail (14.0.0)
+      activerecord (>= 6.0)
+      request_store (~> 1.4)
     parallel (1.23.0)
     parallel_tests (4.2.1)
       parallel
@@ -554,6 +557,7 @@ DEPENDENCIES
   omniauth-oauth2 (~> 1.8)
   omniauth-rails_csrf_protection
   pagy
+  paper_trail (~> 14.0)
   parallel_tests
   pg (>= 0.18, < 2.0)
   pg_search

app/models/application.rb

@@ -5,6 +5,8 @@ class Application < ApplicationRecord
   # within the rails model
   self.ignored_columns = %w[DEPRECATED_cohort]
 
+  has_paper_trail only: %i[lead_provider_approval_status participant_outcome_state]
+
   belongs_to :user
   belongs_to :course
   belongs_to :lead_provider

config/initializers/paper_trail.rb

@@ -0,0 +1 @@
+PaperTrail.serializer = PaperTrail::Serializers::JSON

db/migrate/20230720114510_create_versions.rb

@@ -0,0 +1,37 @@
+# This migration creates the `versions` table, the only schema PT requires.
+# All other migrations PT provides are optional.
+class CreateVersions < ActiveRecord::Migration[6.1]
+  # The largest text column available in all supported RDBMS is
+  # 1024^3 - 1 bytes, roughly one gibibyte.  We specify a size
+  # so that MySQL will use `longtext` instead of `text`.  Otherwise,
+  # when serializing very large objects, `text` might not be big enough.
+  TEXT_BYTES = 1_073_741_823
+
+  def change
+    create_table :versions do |t|
+      t.string   :item_type, null: false
+      t.bigint   :item_id,   null: false
+      t.string   :event,     null: false
+      t.string   :whodunnit
+      t.text     :object, limit: TEXT_BYTES
+
+      # Known issue in MySQL: fractional second precision
+      # -------------------------------------------------
+      #
+      # MySQL timestamp columns do not support fractional seconds unless
+      # defined with "fractional seconds precision". MySQL users should manually
+      # add fractional seconds precision to this migration, specifically, to
+      # the `created_at` column.
+      # (https://dev.mysql.com/doc/refman/5.6/en/fractional-seconds.html)
+      #
+      # MySQL users should also upgrade to at least rails 4.2, which is the first
+      # version of ActiveRecord with support for fractional seconds in MySQL.
+      # (https://github.com/rails/rails/pull/14359)
+      #
+      # MySQL users should use the following line for `created_at`
+      # t.datetime :created_at, limit: 6
+      t.datetime :created_at
+    end
+    add_index :versions, %i[item_type item_id]
+  end
+end

db/schema.rb

@@ -272,4 +272,14 @@
     t.index ["uid"], name: "index_users_on_uid", unique: true
   end
 
+  create_table "versions", force: :cascade do |t|
+    t.string "item_type", null: false
+    t.bigint "item_id", null: false
+    t.string "event", null: false
+    t.string "whodunnit"
+    t.text "object"
+    t.datetime "created_at"
+    t.index ["item_type", "item_id"], name: "index_versions_on_item_type_and_item_id"
+  end
+
 end

spec/models/application_spec.rb

@@ -46,4 +46,23 @@
       end
     end
   end
+
+  describe "versioning" do
+    context "when changing versioned fields" do
+      let(:application) { create(:application, lead_provider_approval_status: "pending", participant_outcome_state: nil) }
+
+      before do
+        application.update!(lead_provider_approval_status: "accepted", participant_outcome_state: "passed")
+      end
+
+      it "has history of changes" do
+        previous_application = application.versions.last.reify
+        expect(application.lead_provider_approval_status).to eq("accepted")
+        expect(application.participant_outcome_state).to eq("passed")
+
+        expect(previous_application.lead_provider_approval_status).to eq("pending")
+        expect(previous_application.participant_outcome_state).to eq(nil)
+      end
+    end
+  end
 end