History log for gitlab subscriptions table

Gitlab_subscriptions table currently doesn't keep history. That makes
blocks data team from measuring some growth KPIs. This MR adds a
history log table

db/migrate/20191127151619_create_gitlab_subscription_histories.rb

+# frozen_string_literal: true
+
+class CreateGitlabSubscriptionHistories < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  def up
+    create_table :gitlab_subscription_histories do |t|
+      t.datetime_with_timezone :gitlab_subscription_created_at
+      t.datetime_with_timezone :gitlab_subscription_updated_at
+      t.date :start_date
+      t.date :end_date
+      t.date :trial_ends_on
+      t.integer :namespace_id, null: true
+      t.integer :hosted_plan_id, null: true
+      t.integer :max_seats_used
+      t.integer :seats
+      t.boolean :trial
+      t.integer :change_type, limit: 2
+      t.bigint :gitlab_subscription_id, null: false
+      t.datetime_with_timezone :created_at
+    end
+    add_index :gitlab_subscription_histories, :gitlab_subscription_id
+  end
+
+  def down
+    drop_table :gitlab_subscription_histories
+  end
+end

db/schema.rb

@@ -1828,6 +1828,23 @@ ActiveRecord::Schema.define(version: 2019_12_02_031812) do
     t.index ["upload_id"], name: "index_geo_upload_deleted_events_on_upload_id"
   end
 
+  create_table "gitlab_subscription_histories", force: :cascade do |t|
+    t.datetime_with_timezone "gitlab_subscription_created_at"
+    t.datetime_with_timezone "gitlab_subscription_updated_at"
+    t.date "start_date"
+    t.date "end_date"
+    t.date "trial_ends_on"
+    t.integer "namespace_id"
+    t.integer "hosted_plan_id"
+    t.integer "max_seats_used"
+    t.integer "seats"
+    t.boolean "trial"
+    t.integer "change_type", limit: 2
+    t.bigint "gitlab_subscription_id", null: false
+    t.datetime_with_timezone "created_at"
+    t.index ["gitlab_subscription_id"], name: "index_gitlab_subscription_histories_on_gitlab_subscription_id"
+  end
+
   create_table "gitlab_subscriptions", force: :cascade do |t|
     t.datetime_with_timezone "created_at", null: false
     t.datetime_with_timezone "updated_at", null: false

ee/app/models/gitlab_subscription.rb

@@ -2,6 +2,9 @@
 
 class GitlabSubscription < ApplicationRecord
   default_value_for(:start_date) { Date.today }
+  after_create_commit :log_previous_state_for_create
+  before_update :log_previous_state_for_update
+  after_destroy_commit :log_previous_state_for_destroy
 
   belongs_to :namespace
   belongs_to :hosted_plan, class_name: 'Plan'
@@ -56,6 +59,32 @@ class GitlabSubscription < ApplicationRecord
 
   private
 
+  def log_previous_state_for_create
+    log_previous_state_to_history(:gitlab_subscription_created)
+  end
+
+  def log_previous_state_for_update
+    attrs = self.attributes.merge(self.attributes_in_database)
+    log_previous_state_to_history(:gitlab_subscription_updated, attrs)
+  end
+
+  def log_previous_state_for_destroy
+    attrs = self.attributes
+    log_previous_state_to_history(:gitlab_subscription_destroyed, attrs)
+  end
+
+  def log_previous_state_to_history(change_type, attrs = {})
+    attrs['gitlab_subscription_created_at'] = attrs['created_at']
+    attrs['gitlab_subscription_updated_at'] = attrs['updated_at']
+    attrs['gitlab_subscription_id'] = self.id
+    attrs['change_type'] = change_type
+
+    omitted_attrs = %w(id created_at updated_at)
+    attrs.reject! { |k, v| omitted_attrs.include?(k) }
+
+    GitlabSubscriptionHistory.create(attrs)
+  end
+
   def hosted?
     namespace_id.present?
   end

ee/app/models/gitlab_subscription_history.rb

+# frozen_string_literal: true
+
+class GitlabSubscriptionHistory < ApplicationRecord
+  enum change_type: [:gitlab_subscription_created,
+                     :gitlab_subscription_updated,
+                     :gitlab_subscription_destroyed]
+end

ee/changelogs/unreleased/13297-track-historical-information-for-the-gitlab_subscriptions-table.yml

+---
+title: Log history for gitlab_subscriptions table
+merge_request: 19694
+author:
+type: added

ee/spec/models/gitlab_subscription_spec.rb

@@ -231,4 +231,68 @@ describe GitlabSubscription do
       end
     end
   end
+
+  describe 'callbacks' do
+    it 'gitlab_subscription columns are contained in gitlab_subscription_history columns' do
+      diff_attrs = %w(updated_at)
+      expect(described_class.attribute_names - GitlabSubscriptionHistory.attribute_names).to eq(diff_attrs)
+    end
+
+    it 'gitlab_subscription_history columns have some extra columns over gitlab_subscription' do
+      diff_attrs = %w(gitlab_subscription_created_at gitlab_subscription_updated_at change_type gitlab_subscription_id)
+      expect(GitlabSubscriptionHistory.attribute_names - described_class.attribute_names).to eq(diff_attrs)
+    end
+
+    context 'after_create_commit' do
+      it 'logs previous state to gitlab subscription history' do
+        subject.save
+
+        expect(GitlabSubscriptionHistory.count).to eq(1)
+        expected_attrs = {
+          'gitlab_subscription_id' => subject.id,
+          'change_type' => 'gitlab_subscription_created'
+        }
+        expect(GitlabSubscriptionHistory.last.attributes).to include(expected_attrs)
+      end
+    end
+
+    context 'before_update' do
+      it 'logs previous state to gitlab subscription history' do
+        subject.update max_seats_used: 42, seats: 13
+        subject.update max_seats_used: 32
+
+        expect(GitlabSubscriptionHistory.count).to eq(2)
+        expected_attrs = {
+          'gitlab_subscription_id' => subject.id,
+          'change_type' => 'gitlab_subscription_updated',
+          'max_seats_used' => 42,
+          'seats' => 13
+        }
+        expect(GitlabSubscriptionHistory.last.attributes).to include(expected_attrs)
+      end
+    end
+
+    context 'after_destroy_commit' do
+      it 'logs previous state to gitlab subscription history' do
+        group = create(:group)
+        plan = create(:bronze_plan)
+        subject.update max_seats_used: 37, seats: 11, namespace: group, hosted_plan: plan
+        db_created_at = described_class.last.created_at
+
+        subject.destroy
+
+        expect(GitlabSubscriptionHistory.count).to eq(2)
+        expected_attrs = {
+          'gitlab_subscription_id' => subject.id,
+          'change_type' => 'gitlab_subscription_destroyed',
+          'max_seats_used' => 37,
+          'seats' => 11,
+          'namespace_id' => group.id,
+          'hosted_plan_id' => plan.id,
+          'gitlab_subscription_created_at' => db_created_at
+        }
+        expect(GitlabSubscriptionHistory.last.attributes).to include(expected_attrs)
+      end
+    end
+  end
 end

spec/db/schema_spec.rb

@@ -43,6 +43,7 @@ describe 'Database schema' do
     geo_nodes: %w[oauth_application_id],
     geo_repository_deleted_events: %w[project_id],
     geo_upload_deleted_events: %w[upload_id model_id],
+    gitlab_subscription_histories: %w[gitlab_subscription_id hosted_plan_id namespace_id],
     import_failures: %w[project_id],
     identities: %w[user_id],
     issues: %w[last_edited_by_id state_id],