Add post migration to update incident issues

- Spec to test behaviour

changelogs/unreleased/229544-populate-issue-type-for-incident-issues.yml

+---
+title: Migrate all 'incident' labelled issues to have issue type 'incident'
+merge_request: 37668
+author:
+type: added

db/post_migrate/20200723040950_migrate_incident_issues_to_incident_type.rb

+# frozen_string_literal: true
+
+class MigrateIncidentIssuesToIncidentType < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+  BATCH_SIZE = 100
+
+  disable_ddl_transaction!
+
+  LABEL_PROPERTIES = {
+    title: 'incident'
+  }.freeze
+
+  class Issue < ActiveRecord::Base
+    include EachBatch
+
+    self.table_name = 'issues'
+
+    scope :incident_labelled, -> do
+      joins("INNER JOIN label_links ON label_links.target_type = 'Issue' AND label_links.target_id = issues.id")
+        .joins("INNER JOIN labels ON labels.id = label_links.label_id")
+        .where(labels: LABEL_PROPERTIES)
+    end
+
+    enum issue_type: {
+      issue: 0,
+      incident: 1
+    }
+
+    scope :incident_typed, -> { where(issue_type: :incident) }
+  end
+
+  def up
+    incident_issues = Issue.incident_labelled
+
+    incident_issues.each_batch(of: BATCH_SIZE) do |batch|
+      batch.update_all(issue_type: :incident)
+    end
+  end
+
+  def down
+    incident_issues = Issue.incident_typed
+
+    incident_issues.each_batch(of: BATCH_SIZE) do |batch|
+      batch.update_all(issue_type: :issue)
+    end
+  end
+end

db/schema_migrations/20200723040950

+085b3ad0f7da78a1e13f5cd3d2e7df297284a682c3bcd3883e487b18497430ff
\ No newline at end of file

spec/migrations/migrate_incident_issues_to_incident_type_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20200723040950_migrate_incident_issues_to_incident_type.rb')
+
+RSpec.describe MigrateIncidentIssuesToIncidentType do
+  let(:migration) { described_class.new }
+
+  let(:projects) { table(:projects) }
+  let(:namespaces) { table(:namespaces) }
+  let(:labels) { table(:labels) }
+  let(:issues) { table(:issues) }
+  let(:label_links) { table(:label_links) }
+  let(:label_props) { IncidentManagement::CreateIncidentLabelService::LABEL_PROPERTIES }
+
+  let(:namespace) { namespaces.create!(name: 'foo', path: 'foo') }
+  let!(:project) { projects.create!(namespace_id: namespace.id) }
+  let(:label) { labels.create!(project_id: project.id, **label_props) }
+  let!(:incident_issue) { issues.create!(project_id: project.id) }
+  let!(:other_issue) { issues.create!(project_id: project.id) }
+
+  # Issue issue_type enum
+  let(:issue_type) { 0 }
+  let(:incident_type) { 1 }
+
+  before do
+    label_links.create!(target_id: incident_issue.id, label_id: label.id, target_type: 'Issue')
+  end
+
+  describe '#up' do
+    it 'updates the incident issue type' do
+      expect { migrate! }
+        .to change { incident_issue.reload.issue_type }
+        .from(issue_type)
+        .to(incident_type)
+
+      expect(other_issue.reload.issue_type).to eql(issue_type)
+    end
+  end
+
+  describe '#down' do
+    let!(:incident_issue) { issues.create!(project_id: project.id, issue_type: issue_type) }
+
+    it 'updates the incident issue type' do
+      migration.up
+
+      expect { migration.down }
+        .to change { incident_issue.reload.issue_type }
+        .from(incident_type)
+        .to(issue_type)
+
+      expect(other_issue.reload.issue_type).to eql(issue_type)
+    end
+  end
+end