Merge pull request #3102 from alphagov/reduce-graphql-queries

Optimise render-time link expansion for GraphQL (all editions, except ministers index page)

app/graphql/sources/linked_to_editions_source.rb

@@ -8,21 +8,22 @@ def initialize(parent_object:)
     # rubocop:enable Lint/MissingSuper
 
     def fetch(link_types)
-      link_set_links = @object.document.link_set_links
-        .includes(target_documents: @content_store) # content_store is :live or :draft (a Document has_one Edition by that name)
-        .where(link_type: link_types)
-        .where(target_documents: { locale: "en" })
+      edition_links = @object.links.order(link_type: :asc, position: :asc)
 
-      edition_links = @object.links
-        .includes(target_documents: @content_store) # content_store is :live or :draft (a Document has_one Edition by that name)
-        .where(link_type: link_types)
-        .where(target_documents: { locale: "en" })
+      all_links = if @object.document.link_set
+                    edition_links.or(@object.document.link_set.links)
+                  else
+                    edition_links
+                  end
 
-      all_links = link_set_links + edition_links
+      all_links_for_link_type_and_locale = all_links
+                                            .includes(target_documents: @content_store) # content_store is :live or :draft (a Document has_one Edition by that name)
+                                            .where(link_type: link_types)
+                                            .where(target_documents: { locale: "en" })
 
       link_types_map = link_types.index_with { [] }
 
-      all_links.each_with_object(link_types_map) { |link, hash|
+      all_links_for_link_type_and_locale.each_with_object(link_types_map) { |link, hash|
         hash[link.link_type].concat(editions_for_link(link))
       }.values
     end

db/migrate/20250128101515_add_edition_link_index.rb

@@ -0,0 +1,5 @@
+class AddEditionLinkIndex < ActiveRecord::Migration[8.0]
+  def change
+    add_index :links, %i[edition_id link_type]
+  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: 2025_01_27_105807) do
+ActiveRecord::Schema[8.0].define(version: 2025_01_28_101515) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_catalog.plpgsql"
 
@@ -159,6 +159,7 @@
     t.datetime "updated_at", precision: nil, null: false
     t.integer "position", default: 0, null: false
     t.integer "edition_id"
+    t.index ["edition_id", "link_type"], name: "index_links_on_edition_id_and_link_type"
     t.index ["edition_id"], name: "index_links_on_edition_id"
     t.index ["link_set_id", "link_type"], name: "index_links_on_link_set_id_and_link_type"
     t.index ["link_set_id", "target_content_id"], name: "index_links_on_link_set_id_and_target_content_id"

spec/graphql/sources/linked_to_editions_source_spec.rb

@@ -33,4 +33,25 @@
       expect(request.load).to eq([target_edition_1, target_edition_3])
     end
   end
+
+  it "returns a mixture of links when both present" do
+    target_edition_1 = create(:edition)
+    target_edition_2 = create(:edition)
+    target_edition_3 = create(:edition)
+
+    source_edition = create(:edition,
+                            links_hash: {
+                              "test_link" => [target_edition_1.content_id],
+                              "another_link_type" => [target_edition_2.content_id],
+                            })
+
+    link_set = create(:link_set, content_id: source_edition.content_id)
+    create(:link, link_set: link_set, target_content_id: target_edition_3.content_id, link_type: "test_link")
+
+    GraphQL::Dataloader.with_dataloading do |dataloader|
+      request = dataloader.with(described_class, parent_object: source_edition).request("test_link")
+
+      expect(request.load).to eq([target_edition_1, target_edition_3])
+    end
+  end
 end