Reduce number of queries when saving form document

Previously, we would run a SQL query per page in the form to get the
next page, and also to get the conditions for the page.

Use `includes` so that we get the pages and all their conditions by
running fewer queries.

Also accept the `next_page` as an argument to
Page#as_form_document_step as we already know what the next_page is
when we call it from Form#as_form_document so we can avoid an
additional query per page.

Author: stephencdaly

app/models/form.rb

@@ -181,7 +181,11 @@ def email_task_status_service
   end
 
   def steps
-    pages.map(&:as_form_document_step)
+    ordered_pages = pages.includes(:routing_conditions).to_a
+    ordered_pages.map.with_index do |page, index|
+      next_page = ordered_pages.fetch(index + 1, nil)
+      page.as_form_document_step(next_page)
+    end
   end
 
   def start_page

app/models/page.rb

@@ -89,11 +89,11 @@ def show_optional_suffix?
     is_optional? && answer_type != "selection"
   end
 
-  def as_form_document_step
+  def as_form_document_step(next_page)
     {
       "id" => id,
       "position" => position,
-      "next_step_id" => next_page,
+      "next_step_id" => next_page&.id,
       "type" => "question_page",
       "data" => slice(*%w[question_text hint_text answer_type is_optional answer_settings page_heading guidance_markdown is_repeatable]),
       "routing_conditions" => routing_conditions.map(&:as_form_document_condition),

spec/models/form_document/step_spec.rb

@@ -4,14 +4,15 @@
   subject(:form_document_step) { described_class.new(page_as_form_document_step) }
 
   let(:page) { create :page }
-  let(:page_as_form_document_step) { page.as_form_document_step }
+  let(:next_page) { create :page }
+  let(:page_as_form_document_step) { page.as_form_document_step(next_page) }
 
   it "ignores any attributes that are not defined" do
     expect(described_class.new(foo: "bar").attributes).not_to include(:foo)
   end
 
-  it "has the position and next page ID from the original page" do
-    expect(form_document_step).to have_attributes(position: page.position, next_step_id: page.next_page)
+  it "has the position and next page ID from the form_document_step" do
+    expect(form_document_step).to have_attributes(position: page.position, next_step_id: next_page.id)
   end
 
   it "has all question attributes the original page has" do

spec/models/page_spec.rb

@@ -664,27 +664,33 @@
     let!(:second_page) { create :page, form: }
 
     it "has an id" do
-      expect(page.as_form_document_step).to match a_hash_including("id" => page.id)
+      expect(page.as_form_document_step(second_page)).to match a_hash_including("id" => page.id)
     end
 
     it "has a position" do
-      expect(page.as_form_document_step).to match a_hash_including("position" => page.position)
+      expect(page.as_form_document_step(second_page)).to match a_hash_including("position" => page.position)
     end
 
     it "has a next_step_id" do
-      expect(page.as_form_document_step).to match a_hash_including("next_step_id" => second_page.id)
+      expect(page.as_form_document_step(second_page)).to match a_hash_including("next_step_id" => second_page.id)
     end
 
     it "includes all attributes for the page as a step" do
       page_attributes = described_class.attribute_names - %w[id form_id next_page position created_at updated_at]
-      expect(page.as_form_document_step["data"]).to match a_hash_including(*page_attributes)
+      expect(page.as_form_document_step(second_page)["data"]).to match a_hash_including(*page_attributes)
     end
 
     context "when there are conditions associated with the page" do
       let!(:condition) { create :condition, routing_page_id: page.id, check_page_id: page.id }
 
       it "includes the routing conditions" do
-        expect(page.reload.as_form_document_step["routing_conditions"]).to include(condition.as_form_document_condition)
+        expect(page.reload.as_form_document_step(second_page)["routing_conditions"]).to include(condition.as_form_document_condition)
+      end
+    end
+
+    context "when the provided next_page is nil" do
+      it "has nil next_step_id" do
+        expect(page.as_form_document_step(nil)["next_step_id"]).to be_nil
       end
     end
   end

spec/services/step_summary_card_service_spec.rb

@@ -7,7 +7,7 @@
 
   let(:form_document_content) { FormDocument::Content.from_form_document(form.live_form_document) }
   let(:form_document_steps) { form_document_content.steps }
-  let(:form_document_step) { FormDocument::Step.new(page.as_form_document_step) }
+  let(:form_document_step) { FormDocument::Step.new(page.as_form_document_step(nil)) }
 
   let(:form) { create :form, :live }