Avoid preloading triages

This avoids potential issues where preloading large amounts of data can
be slow and require a lot of memory. Instead, where N+1 issues isn't a
problem, it's fine to run an additional query to the database and fetch
only the data we need as is the case in most situations.

Author: thomasleese

app/components/app_outcome_banner_component.rb

@@ -63,7 +63,13 @@ def vaccination_record
   end
 
   def triage
-    @triage ||= patient.latest_triage(programme:)
+    @triage ||=
+      patient
+        .triages
+        .not_invalidated
+        .includes(:performed_by)
+        .order(created_at: :desc)
+        .find_by(programme:)
   end
 
   def session_attendance

app/components/app_triage_form_component.rb

@@ -13,21 +13,17 @@ def initialize(
 
     @patient_session = patient_session
     @programme = programme
-    @triage =
-      triage ||
-        Triage.new.tap do |t|
-          if (latest_triage = patient_session.patient.latest_triage(programme:))
-            t.status = latest_triage.status
-          end
-        end
+    @triage = triage || default_triage
     @url = url
     @method = method
     @legend = legend
   end
 
   private
 
-  attr_reader :programme
+  attr_reader :patient_session, :programme
+
+  delegate :patient, to: :patient_session
 
   def fieldset_options
     text = "Is it safe to vaccinate #{@patient_session.patient.given_name}?"
@@ -41,4 +37,15 @@ def fieldset_options
       { legend: { text:, size: "s", class: "app-fieldset__legend--reset" } }
     end
   end
+
+  def default_triage
+    previous_triage =
+      patient
+        .triages
+        .not_invalidated
+        .order(created_at: :desc)
+        .find_by(programme:)
+
+    Triage.new(status: previous_triage&.status)
+  end
 end

app/controllers/patients_controller.rb

@@ -71,7 +71,6 @@ def set_patient
         :gp_practice,
         :organisation,
         :school,
-        :triages,
         consents: %i[parent patient],
         parent_relationships: :parent,
         patient_sessions: %i[location session_attendances]

app/jobs/school_session_reminders_job.rb

@@ -9,7 +9,7 @@ def perform
     patient_sessions =
       PatientSession
         .includes(
-          patient: [:parents, :triages, { consents: %i[parent patient] }],
+          patient: [:parents, { consents: %i[parent patient] }],
           session: :programmes
         )
         .eager_load(:session)

app/models/patient.rb

@@ -73,7 +73,7 @@ class Patient < ApplicationRecord
   has_many :school_moves
   has_many :session_notifications
   has_many :triage_statuses
-  has_many :triages, -> { order(:created_at) }
+  has_many :triages
   has_many :vaccination_records, -> { kept }
   has_many :vaccination_statuses
 
@@ -277,13 +277,6 @@ def triage_status(programme:)
       triage_statuses.build(programme:)
   end
 
-  def latest_triage(programme:)
-    triages
-      .select { it.programme_id == programme.id }
-      .reject(&:invalidated?)
-      .max_by(&:created_at)
-  end
-
   def vaccination_status(programme:)
     # Use `find` to allow for preloading.
     vaccination_statuses.find { it.programme_id == programme.id } ||

app/models/patient/triage_status.rb

@@ -29,7 +29,9 @@ class Patient::TriageStatus < ApplicationRecord
            end,
            through: :patient
 
-  has_many :triages, -> { not_invalidated }, through: :patient
+  has_many :triages,
+           -> { not_invalidated.order(created_at: :desc) },
+           through: :patient
 
   has_many :vaccination_records,
            -> { kept.order(performed_at: :desc) },
@@ -95,6 +97,6 @@ def status_should_be_required?
   end
 
   def latest_triage
-    @latest_triage ||= triages.select { it.programme_id == programme_id }.last
+    @latest_triage ||= triages.find { it.programme_id == programme_id }
   end
 end

app/models/patient/vaccination_status.rb

@@ -29,7 +29,9 @@ class Patient::VaccinationStatus < ApplicationRecord
            end,
            through: :patient
 
-  has_many :triages, -> { not_invalidated }, through: :patient
+  has_many :triages,
+           -> { not_invalidated.order(created_at: :desc) },
+           through: :patient
 
   has_many :vaccination_records,
            -> { kept.order(performed_at: :desc) },

app/models/patient_session/vaccination_status.rb

@@ -31,7 +31,9 @@ class PatientSession::VaccinationStatus < ApplicationRecord
            end,
            through: :patient
 
-  has_many :triages, -> { not_invalidated }, through: :patient
+  has_many :triages,
+           -> { not_invalidated.order(created_at: :desc) },
+           through: :patient
 
   has_many :vaccination_records,
            -> { kept.order(performed_at: :desc) },