SELECT subset of columns for role_appointments

This "optimisation" is specific to the ministers index type.

We've followed the patterns established in the root Edition and the more
generic Link sources. The big differences are mostly down to
* the larger number of JOINs used in this query
* the convenience of only needing to handle link set links here
* this data loader fetches a person's roles but is actually invoked from
  the person's role_appointments field... weird

Because of the large number of JOINS, we've resorted to supplying SQL
strings in order to provide our own, hopefully clearer, join table
aliases (as opposed to leaving that to Active Record to generate).

app/graphql/sources/person_current_roles_source.rb

@@ -1,51 +1,78 @@
 module Sources
   class PersonCurrentRolesSource < GraphQL::Dataloader::Source
-    def fetch(person_content_ids)
+    # rubocop:disable Lint/MissingSuper
+    def initialize
+      @content_store = :live
+    end
+    # rubocop:enable Lint/MissingSuper
+
+    def fetch(person_content_ids_and_selections)
+      person_content_ids = []
+      ids_map = {}
+      all_selections = {
+        role_appointment_links: %i[target_content_id],
+        documents: %i[content_id],
+      }
+      editions_selections = Set.new
+
+      person_content_ids_and_selections.each do |person_content_id, selections|
+        person_content_ids << person_content_id
+        ids_map[person_content_id] = []
+        editions_selections.merge(selections)
+      end
+
+      all_selections[:editions] = editions_selections.to_a
+
       all_roles = Edition
-        .live
-        .includes(
-          document: {
-            reverse_links: { # role -> role_appointment
-              link_set: {
-                documents: [
-                  :editions, # role_appointment
-                  :link_set_links, # role_appointment -> person
-                ],
-              },
-            },
-          },
+        .joins(document: [reverse_links: :link_set])
+        .joins(
+          <<~SQL
+            INNER JOIN documents role_appointment_documents
+            ON role_appointment_documents.content_id = link_sets.content_id
+          SQL
+        )
+        .joins(
+          <<~SQL
+            INNER JOIN editions role_appointment_editions
+            ON role_appointment_editions.document_id = role_appointment_documents.id
+          SQL
+        )
+        .joins(
+          <<~SQL
+            INNER JOIN link_sets role_appointment_link_sets
+            ON role_appointment_link_sets.content_id = role_appointment_documents.content_id
+          SQL
+        )
+        .joins(
+          <<~SQL
+            INNER JOIN links role_appointment_links
+            ON role_appointment_links.link_set_id = role_appointment_link_sets.id
+          SQL
         )
         .where(
-          document_type: "ministerial_role",
-          document: { locale: "en" },
+          editions: {
+            content_store: @content_store,
+            document_type: "ministerial_role",
+          },
+          documents: { locale: "en" },
           reverse_links: { link_type: "role" },
-          documents: { locale: "en" }, # role_appointment Documents
-          editions_documents: { document_type: "role_appointment" }, # role_appointment Editions
-          link_set_links: { target_content_id: person_content_ids, link_type: "person" },
+          role_appointment_documents: { locale: "en" },
+          role_appointment_editions: {
+            content_store: @content_store,
+            document_type: "role_appointment",
+          },
+          role_appointment_links: {
+            target_content_id: person_content_ids,
+            link_type: "person",
+          },
         )
-        .where("editions_documents.details ->> 'current' = 'true'") # editions_documents is the alias that Active Record gives to the role_appointment Editions in the SQL query
+        .where("role_appointment_editions.details ->> 'current' = 'true'")
         .order(reverse_links: { position: :asc })
-
-      ids_map = person_content_ids.index_with { [] }
+        .select(all_selections)
 
       all_roles.each_with_object(ids_map) { |role, hash|
-        hash[person_content_id_for_role(role)] << role
+        hash[role.target_content_id] << role
       }.values
     end
-
-  private
-
-    def person_content_id_for_role(role)
-      role_appointment_documents_for_role(role)
-        .flat_map(&:link_set_links)
-        .find { |link| link.link_type == "person" } # role_appointment -> person
-        .target_content_id
-    end
-
-    def role_appointment_documents_for_role(role)
-      role.document.reverse_links
-        .select { |link| link.link_type == "role" } # role -> role_appointment
-        .flat_map { |link| link.link_set.documents }
-    end
   end
 end

app/graphql/types/ministers_index_type.rb

@@ -51,11 +51,21 @@ class MinistersIndexPersonDetails < Types::BaseObject
       end
 
       class MinistersIndexPersonLinks < Types::BaseObject
-        field :role_appointments, [MinistersIndexRoleAppointment]
+        field :role_appointments, [MinistersIndexRoleAppointment], extras: [:lookahead]
+
+        def role_appointments(lookahead:)
+          links_lookahead = lookahead.selections.find { _1.name == :links }
+          role_lookahead = links_lookahead.selections.find { _1.name == :role }
+
+          selections = convert_edition_selections(lookahead: role_lookahead)
+
+          if role_lookahead.selects?(:links)
+            selections << :id
+            selections << :content_store
+          end
 
-        def role_appointments
           dataloader.with(Sources::PersonCurrentRolesSource)
-            .load(object.content_id)
+            .load([object.content_id, selections])
         end
       end
 

spec/graphql/sources/person_current_roles_source_spec.rb

@@ -11,7 +11,10 @@
     appoint_person_to_role(person_1, role_3)
 
     GraphQL::Dataloader.with_dataloading do |dataloader|
-      request = dataloader.with(described_class).request(person_1.content_id)
+      request = dataloader.with(described_class).request([
+        person_1.content_id,
+        %i[id base_path title details],
+      ])
 
       expect(request.load).to eq([role_1, role_3])
     end