use .size instead of .count and memoize emancipation category count (#6496)

To avoid n+1 queries on the index page, eager load the casa_case_emancipation_categories in the controller, and then use .size instead of .count in the decorator.  Also memoized the emancipation_category_total_count so that we don't have to query for it for every row.

Author: Andrew Camp

app/controllers/casa_cases_controller.rb

@@ -6,7 +6,7 @@ class CasaCasesController < ApplicationController
 
   def index
     authorize CasaCase
-    org_cases = current_user.casa_org.casa_cases.includes(:assigned_volunteers)
+    org_cases = current_user.casa_org.casa_cases.includes(:assigned_volunteers, :casa_case_emancipation_categories)
     @casa_cases = policy_scope(org_cases).includes([:hearing_type, :judge])
     @casa_cases_filter_id = policy(CasaCase).can_see_filters? ? "casa-cases" : ""
     @duties = OtherDuty.where(creator_id: current_user.id)

app/decorators/casa_case_decorator.rb

@@ -114,7 +114,7 @@ def unsuccessful_contacts_this_week_before(date)
   end
 
   def emancipation_checklist_count
-    "#{object.casa_case_emancipation_categories.count} / #{EmancipationCategory.count}"
+    "#{object.casa_case_emancipation_categories.size} / #{h.emancipation_category_total_count}"
   end
 
   def show_contact_type?(contact_type_id)

app/helpers/emancipations_helper.rb

@@ -1,4 +1,10 @@
 module EmancipationsHelper
+  # Memoized per request so the casa_cases index doesn't re-issue COUNT(*)
+  # for every transition-age row when rendering the emancipation badge.
+  def emancipation_category_total_count
+    @emancipation_category_total_count ||= EmancipationCategory.count
+  end
+
   def emancipation_category_checkbox_checked(casa_case, emancipation_category)
     case_contains_category?(casa_case, emancipation_category) ? "checked" : nil
   end

spec/decorators/casa_case_decorator_spec.rb

@@ -102,7 +102,7 @@
 
       expect(casa_case).to(
         receive(:casa_case_emancipation_categories).and_return(
-          double(:categories, count: 2)
+          double(:categories, size: 2)
         )
       )
       expect(EmancipationCategory).to receive(:count).and_return(5)