Use validate_false option

Use new option introduced in https://gitlab.com/gitlab-org/gitlab/merge_requests/22282 which allows a
concurrent foreign key constraint to be added without
validating, which gives the opportunity to fix existing
invalid rows before validating.

changelogs/unreleased/32326-cablett-epic-source-fks.yml

+---
+title: Add epic milestone sourcing foreign key
+merge_request: 21907
+author:
+type: fixed

db/migrate/20191216074800_add_epic_date_sourcing_milestone_indexes.rb

+# frozen_string_literal: true
+
+class AddEpicDateSourcingMilestoneIndexes < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :epics, due_date_column
+    add_concurrent_index :epics, start_date_column
+  end
+
+  def down
+    remove_concurrent_index :epics, start_date_column
+    remove_concurrent_index :epics, due_date_column
+  end
+
+  private
+
+  def due_date_column
+    :due_date_sourcing_milestone_id
+  end
+
+  def start_date_column
+    :start_date_sourcing_milestone_id
+  end
+end

db/migrate/20191216074802_add_epic_start_date_sourcing_milestone_id_foreign_key.rb

+# frozen_string_literal: true
+
+class AddEpicStartDateSourcingMilestoneIdForeignKey < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_foreign_key :epics, :milestones, column: start_date_column, on_delete: :nullify, validate: false
+  end
+
+  def down
+    remove_foreign_key_if_exists :epics, column: start_date_column
+  end
+
+  private
+
+  def start_date_column
+    :start_date_sourcing_milestone_id
+  end
+end

db/migrate/20191216074803_add_epic_due_date_sourcing_milestone_id_foreign_key.rb

+# frozen_string_literal: true
+
+class AddEpicDueDateSourcingMilestoneIdForeignKey < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_foreign_key :epics, :milestones, column: due_date_column, on_delete: :nullify, validate: false
+  end
+
+  def down
+    remove_foreign_key_if_exists :epics, column: due_date_column
+  end
+
+  private
+
+  def due_date_column
+    :due_date_sourcing_milestone_id
+  end
+end

db/migrate/20200110089001_fix_invalid_epic_sourcing_milestone_ids.rb

+# frozen_string_literal: true
+
+class FixInvalidEpicSourcingMilestoneIds < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  def up
+    nullify_invalid_data(:start_date_sourcing_milestone_id)
+    nullify_invalid_data(:due_date_sourcing_milestone_id)
+  end
+
+  def down
+    # no-op
+  end
+
+  private
+
+  def nullify_invalid_data(column_name)
+    execute(<<-SQL.squish)
+      UPDATE epics
+      SET #{column_name} = null
+      WHERE #{column_name} NOT IN (SELECT id FROM milestones);
+    SQL
+  end
+end

db/migrate/20200110090153_validate_foreign_key_epic_start_date_sourcing_milestone.rb

+# frozen_string_literal: true
+
+class ValidateForeignKeyEpicStartDateSourcingMilestone < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    validate_foreign_key(:epics, :start_date_sourcing_milestone_id)
+  end
+
+  def down
+    # no-op
+  end
+end

db/migrate/20200110203532_validate_foreign_key_epic_due_date_sourcing_milestone.rb

+# frozen_string_literal: true
+
+class ValidateForeignKeyEpicDueDateSourcingMilestone < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    validate_foreign_key(:epics, :due_date_sourcing_milestone_id)
+  end
+
+  def down
+    # no-op
+  end
+end

db/schema.rb

@@ -1573,6 +1573,7 @@ ActiveRecord::Schema.define(version: 2020_01_14_113341) do
     t.index ["author_id"], name: "index_epics_on_author_id"
     t.index ["closed_by_id"], name: "index_epics_on_closed_by_id"
     t.index ["due_date_sourcing_epic_id"], name: "index_epics_on_due_date_sourcing_epic_id", where: "(due_date_sourcing_epic_id IS NOT NULL)"
+    t.index ["due_date_sourcing_milestone_id"], name: "index_epics_on_due_date_sourcing_milestone_id"
     t.index ["end_date"], name: "index_epics_on_end_date"
     t.index ["group_id"], name: "index_epics_on_group_id"
     t.index ["iid"], name: "index_epics_on_iid"
@@ -1580,6 +1581,7 @@ ActiveRecord::Schema.define(version: 2020_01_14_113341) do
     t.index ["parent_id"], name: "index_epics_on_parent_id"
     t.index ["start_date"], name: "index_epics_on_start_date"
     t.index ["start_date_sourcing_epic_id"], name: "index_epics_on_start_date_sourcing_epic_id", where: "(start_date_sourcing_epic_id IS NOT NULL)"
+    t.index ["start_date_sourcing_milestone_id"], name: "index_epics_on_start_date_sourcing_milestone_id"
   end
 
   create_table "events", id: :serial, force: :cascade do |t|
@@ -4587,6 +4589,8 @@ ActiveRecord::Schema.define(version: 2020_01_14_113341) do
   add_foreign_key "epics", "epics", column: "due_date_sourcing_epic_id", name: "fk_013c9f36ca", on_delete: :nullify
   add_foreign_key "epics", "epics", column: "parent_id", name: "fk_25b99c1be3", on_delete: :cascade
   add_foreign_key "epics", "epics", column: "start_date_sourcing_epic_id", name: "fk_9d480c64b2", on_delete: :nullify
+  add_foreign_key "epics", "milestones", column: "due_date_sourcing_milestone_id", name: "fk_3c1fd1cccc", on_delete: :nullify
+  add_foreign_key "epics", "milestones", column: "start_date_sourcing_milestone_id", name: "fk_1fbed67632", on_delete: :nullify
   add_foreign_key "epics", "milestones", on_delete: :nullify
   add_foreign_key "epics", "namespaces", column: "group_id", name: "fk_f081aa4489", on_delete: :cascade
   add_foreign_key "epics", "users", column: "assignee_id", name: "fk_dccd3f98fc", on_delete: :nullify

ee/spec/db/schema_support.rb

@@ -13,7 +13,7 @@ module EE
           approvers: %w[target_id user_id],
           boards: %w[milestone_id],
           draft_notes: %w[discussion_id],
-          epics: %w[updated_by_id last_edited_by_id start_date_sourcing_milestone_id due_date_sourcing_milestone_id],
+          epics: %w[updated_by_id last_edited_by_id],
           geo_event_log: %w[hashed_storage_attachments_event_id],
           geo_job_artifact_deleted_events: %w[job_artifact_id],
           geo_lfs_object_deleted_events: %w[lfs_object_id],

spec/db/schema_spec.rb

@@ -34,7 +34,7 @@ describe 'Database schema' do
     draft_notes: %w[discussion_id commit_id],
     emails: %w[user_id],
     events: %w[target_id],
-    epics: %w[updated_by_id last_edited_by_id start_date_sourcing_milestone_id due_date_sourcing_milestone_id state_id],
+    epics: %w[updated_by_id last_edited_by_id state_id],
     forked_project_links: %w[forked_from_project_id],
     geo_event_log: %w[hashed_storage_attachments_event_id],
     geo_job_artifact_deleted_events: %w[job_artifact_id],