Allow offsite links to have many parents

In order to enable standard editions - which are editionable - to be associated with offsite links, we are introducing a join table.

This will allow an offsite link to be associated with multiple editions.
This should not introduce any behavioural changes to organisations, topical events or world location news.

Author: eYinka

app/controllers/admin/offsite_links_controller.rb

@@ -7,7 +7,7 @@ def new
   end
 
   def create
-    @offsite_link = OffsiteLink.new(offsite_link_params.merge(parent: @parent))
+    @offsite_link = @parent.offsite_links.create(offsite_link_params)
 
     if @offsite_link.save
       flash[:notice] = "An offsite link has been created for #{@parent.name}"

app/models/offsite_link.rb

@@ -56,15 +56,31 @@ def self.display_type(link_type)
 
   date_attributes(:date)
 
-  belongs_to :parent, polymorphic: true
+  has_many :offsite_link_parents
+  has_many :organisations, through: :offsite_link_parents, source: :parent, source_type: "Organisation"
+  has_many :topical_events, through: :offsite_link_parents, source: :parent, source_type: "TopicalEvent"
+  has_many :world_location_news, through: :offsite_link_parents, source: :parent, source_type: "WorldLocationNews"
+
   has_many :features, inverse_of: :offsite_link, dependent: :destroy
 
-  after_commit :republish_parent_to_publishing_api
+  after_commit :republish_parents_to_publishing_api
 
   validates :title, :summary, :link_type, :url, presence: true, length: { maximum: 255 }
   validate :check_url_is_allowed
   validates :link_type, presence: true, inclusion: { in: LinkTypes.all }
 
+  # We only expect one type of parent per offsite link (either organisations, or topical events, or world location news).
+  # Once topical events become editionable, the parents will return all editions associated with the offsite link.
+  def parents
+    organisations + topical_events + world_location_news
+  end
+
+  # For non-editionable parents, we are returning the last - and only - parent.
+  # Once topical events become editionable, this will return the last associated edition.
+  def parent
+    parents.last
+  end
+
   def check_url_is_allowed
     if (uri = Addressable::URI.parse(url))
       host = uri.host
@@ -111,7 +127,7 @@ def url_is_permitted?(host)
     PERMITTED_HOSTS.any? { |permitted_host| host =~ /(?:^|\.)#{permitted_host}$/ }
   end
 
-  def republish_parent_to_publishing_api
+  def republish_parents_to_publishing_api
     Whitehall::PublishingApi.republish_async(parent)
   end
 end

app/models/offsite_link_parent.rb

@@ -0,0 +1,4 @@
+class OffsiteLinkParent < ApplicationRecord
+  belongs_to :parent, polymorphic: true
+  belongs_to :offsite_link
+end

app/models/organisation.rb

@@ -109,7 +109,8 @@ class Organisation < ApplicationRecord
   has_and_belongs_to_many :superseding_organisations, class_name: "Organisation", foreign_key: :superseded_organisation_id, join_table: :organisation_supersedings, association_foreign_key: :superseding_organisation_id
   has_and_belongs_to_many :superseded_organisations, class_name: "Organisation", foreign_key: :superseding_organisation_id, join_table: :organisation_supersedings, association_foreign_key: :superseded_organisation_id
 
-  has_many :offsite_links, as: :parent
+  has_many :offsite_link_parents, as: :parent
+  has_many :offsite_links, through: :offsite_link_parents
 
   def featured_documents_display_limit
     return 7 if slug == "prime-ministers-office-10-downing-street"

app/models/topical_event.rb

@@ -29,7 +29,8 @@ class TopicalEvent < ApplicationRecord
 
   MAX_FEATURED_DOCUMENTS = 6
   has_many :features, inverse_of: :topical_event, dependent: :destroy
-  has_many :offsite_links, as: :parent
+  has_many :offsite_link_parents, as: :parent
+  has_many :offsite_links, through: :offsite_link_parents
   has_many :social_media_accounts, as: :socialable, dependent: :destroy
 
   has_many :topical_event_organisations, -> { extending UserOrderableExtension }

app/models/world_location_news.rb

@@ -16,8 +16,9 @@ class WorldLocationNews < ApplicationRecord
   delegate :slug, :slug=, to: :world_location
 
   has_many :featured_links, -> { order(:created_at) }, as: :linkable, dependent: :destroy
+  has_many :offsite_link_parents, as: :parent
+  has_many :offsite_links, through: :offsite_link_parents
   accepts_nested_attributes_for :featured_links, reject_if: ->(attributes) { attributes["url"].blank? }, allow_destroy: true
-  has_many :offsite_links, as: :parent
   accepts_nested_attributes_for :offsite_links
 
   translates :title, :mission_statement

db/migrate/20260121113213_add_offsite_link_parents.rb

@@ -0,0 +1,13 @@
+class AddOffsiteLinkParents < ActiveRecord::Migration[8.0]
+  def change
+    create_table :offsite_link_parents do |t|
+      t.references :offsite_link, null: false
+      t.references :parent, polymorphic: true, null: false
+      t.timestamps
+    end
+
+    add_index :offsite_link_parents,
+              [:parent_type, :parent_id, :offsite_link_id],
+              unique: true
+  end
+end

db/migrate/20260121122256_add_data_migration_for_offsite_link_parents.rb

@@ -0,0 +1,16 @@
+class AddDataMigrationForOffsiteLinkParents < ActiveRecord::Migration[8.0]
+  def up
+    safety_assured do
+      execute <<-SQL
+        INSERT INTO offsite_link_parents (offsite_link_id, parent_id, parent_type, created_at, updated_at)
+        SELECT id, parent_id, parent_type, NOW(), NOW()
+        FROM offsite_links AS ol
+        WHERE NOT EXISTS (
+            SELECT 1
+            FROM offsite_link_parents AS olp
+            WHERE olp.offsite_link_id = ol.id
+          );
+      SQL
+    end
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_01_07_195134) do
+ActiveRecord::Schema[8.0].define(version: 2026_01_21_122256) do
   create_table "assets", charset: "utf8mb4", collation: "utf8mb4_unicode_ci", force: :cascade do |t|
     t.string "asset_manager_id", null: false
     t.string "variant", null: false
@@ -653,6 +653,17 @@
     t.index ["nation_id"], name: "index_nation_inapplicabilities_on_nation_id"
   end
 
+  create_table "offsite_link_parents", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "offsite_link_id", null: false
+    t.string "parent_type", null: false
+    t.bigint "parent_id", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["offsite_link_id"], name: "index_offsite_link_parents_on_offsite_link_id"
+    t.index ["parent_type", "parent_id", "offsite_link_id"], name: "idx_on_parent_type_parent_id_offsite_link_id_c4a8862347", unique: true
+    t.index ["parent_type", "parent_id"], name: "index_offsite_link_parents_on_parent"
+  end
+
   create_table "offsite_links", id: :integer, charset: "utf8mb4", collation: "utf8mb4_unicode_ci", force: :cascade do |t|
     t.string "title"
     t.string "summary"

features/step_definitions/topical_event_featurings_steps.rb

@@ -1,5 +1,5 @@
 Given(/^the topical event has an offsite link with the title "([^"]*)"$/) do |title|
-  create(:offsite_link, parent_type: "TopicalEvent", parent: @topical_event, title:)
+  create(:offsite_link, topical_events: [@topical_event], title:)
 end
 
 When(/^I visit the topical event featuring index page$/) do
@@ -13,8 +13,8 @@
 
 And(/^two featurings exist for "([^"]*)"$/) do |name|
   topical_event = TopicalEvent.find_by(name:)
-  offsite_link1 = create(:offsite_link, parent_type: "TopicalEvent", parent: topical_event, title: "Featured link 1")
-  offsite_link2 = create(:offsite_link, parent_type: "TopicalEvent", parent: topical_event, title: "Featured link 2")
+  offsite_link1 = create(:offsite_link, topical_events: [topical_event], title: "Featured link 1")
+  offsite_link2 = create(:offsite_link, topical_events: [topical_event], title: "Featured link 2")
   create(:offsite_topical_event_featuring, topical_event:, offsite_link: offsite_link1)
   create(:offsite_topical_event_featuring, topical_event:, offsite_link: offsite_link2)
 end