Replace session attendance patient session foreign key

This replaces the foreign key association between session attendances
and patient sessions to instead link directly to the patient. This is
needed as we eventually want to replace the PatientSession model and to
do that we need to make sure all foreign keys to it have been replaced.

The functionality should be the same before and after.

Jira-Issue: MAV-1820

Author: thomasleese

app/controllers/patient_sessions/session_attendances_controller.rb

@@ -43,10 +43,13 @@ def update
 
   def set_session_attendance
     @session_attendance =
-      authorize @patient_session
-                  .session_attendances
-                  .includes(:patient, :session_date)
-                  .find_or_initialize_by(session_date: @session_date)
+      authorize(
+        @patient
+          .session_attendances
+          .includes(:patient, :session_date)
+          .find_or_initialize_by(session_date: @session_date)
+          .tap { it.patient_session = @patient_session }
+      )
   end
 
   def session_attendance_params

app/lib/generate/vaccination_records.rb

@@ -23,17 +23,20 @@ def create_vaccinations
     vaccination_records = []
 
     random_patient_sessions.each do |patient_session|
-      patient_session_id = patient_session.id
-      session_date_ids = patient_session.session.session_dates.pluck(:id)
-
-      unless SessionAttendance.exists?(
-               patient_session_id:,
-               session_date_id: session_date_ids
+      patient = patient_session.patient
+      session = patient_session.session
+
+      unless SessionAttendance.joins(:session_date).exists?(
+               patient:,
+               session_date: {
+                 session:
+               }
              )
         session_attendances << FactoryBot.build(
           :session_attendance,
           :present,
-          patient_session:
+          patient:,
+          session:
         )
       end
 

app/models/patient.rb

@@ -65,6 +65,7 @@ class Patient < ApplicationRecord
   has_many :consent_notifications
   has_many :consent_statuses
   has_many :consents
+  has_many :gillick_assessments
   has_many :notes
   has_many :notify_log_entries
   has_many :parent_relationships, -> { order(:created_at) }
@@ -73,16 +74,15 @@ class Patient < ApplicationRecord
   has_many :pre_screenings
   has_many :school_move_log_entries
   has_many :school_moves
+  has_many :session_attendances
   has_many :session_notifications
   has_many :triage_statuses
   has_many :triages
   has_many :vaccination_records, -> { kept }
   has_many :vaccination_statuses
 
-  has_many :gillick_assessments
   has_many :parents, through: :parent_relationships
   has_many :patient_specific_directions
-  has_many :session_attendances, through: :patient_sessions
   has_many :sessions, through: :patient_sessions
   has_many :teams, -> { distinct }, through: :sessions
 

app/models/patient_session.rb

@@ -44,7 +44,6 @@ class PatientSession < ApplicationRecord
   belongs_to :patient
   belongs_to :session
 
-  has_many :session_attendances, dependent: :destroy
   has_one :registration_status
 
   has_one :location, through: :session
@@ -67,6 +66,10 @@ class PatientSession < ApplicationRecord
            -> { where(patient_id: it.patient_id) },
            through: :session
 
+  has_many :session_attendances,
+           -> { where(patient_id: it.patient_id) },
+           through: :session
+
   has_many :session_notifications,
            -> { where(session_id: it.session_id) },
            through: :patient
@@ -286,9 +289,11 @@ def programmes = session.programmes_for(patient:, academic_year:)
 
   def todays_attendance
     if (session_date = session.session_dates.today.first)
-      session_attendances.includes(:session_date).find_or_initialize_by(
-        session_date:
-      )
+      patient
+        .session_attendances
+        .includes(:session_date)
+        .find_or_initialize_by(session_date:)
+        .tap { it.patient_session = self }
     end
   end
 

app/models/patient_session/registration_status.rb

@@ -27,8 +27,14 @@ class PatientSession::RegistrationStatus < ApplicationRecord
            through: :patient
 
   has_one :session_attendance,
-          -> { today },
-          through: :patient_session,
+          -> do
+            today.where(
+              session_dates: {
+                session_id: it.patient_session.session_id
+              }
+            )
+          end,
+          through: :patient,
           source: :session_attendances
 
   enum :status,

app/models/session.rb

@@ -55,6 +55,7 @@ class Session < ApplicationRecord
   has_many :programmes, through: :session_programmes
   has_many :gillick_assessments, through: :session_dates
   has_many :patients, through: :patient_sessions
+  has_many :session_attendances, through: :session_dates
   has_many :vaccines, through: :programmes
 
   has_many :location_programme_year_groups,

app/models/session_attendance.rb

@@ -4,32 +4,36 @@
 #
 # Table name: session_attendances
 #
-#  id                 :bigint           not null, primary key
-#  attending          :boolean          not null
-#  created_at         :datetime         not null
-#  updated_at         :datetime         not null
-#  patient_session_id :bigint           not null
-#  session_date_id    :bigint           not null
+#  id              :bigint           not null, primary key
+#  attending       :boolean          not null
+#  created_at      :datetime         not null
+#  updated_at      :datetime         not null
+#  patient_id      :bigint           not null
+#  session_date_id :bigint           not null
 #
 # Indexes
 #
-#  idx_on_patient_session_id_session_date_id_be8bd21ddf  (patient_session_id,session_date_id) UNIQUE
-#  index_session_attendances_on_session_date_id          (session_date_id)
+#  index_session_attendances_on_patient_id       (patient_id)
+#  index_session_attendances_on_session_date_id  (session_date_id)
 #
 # Foreign Keys
 #
-#  fk_rails_...  (patient_session_id => patient_sessions.id)
+#  fk_rails_...  (patient_id => patients.id)
 #  fk_rails_...  (session_date_id => session_dates.id)
 #
 class SessionAttendance < ApplicationRecord
-  audited associated_with: :patient_session
+  audited associated_with: :patient
 
-  belongs_to :patient_session
+  belongs_to :patient
   belongs_to :session_date
 
-  has_one :session, through: :patient_session
-  has_one :patient, through: :patient_session
+  has_one :session, through: :session_date
   has_one :location, through: :session
 
   scope :today, -> { joins(:session_date).merge(SessionDate.today) }
+
+  # This is a bit of a hack, but it allows the SessionAttendancePolicy class
+  # to have access to the patient session which has already been fetched from
+  # the database elsewhere.
+  attr_accessor :patient_session
 end

db/migrate/20250821135954_remove_patient_session_from_session_attendances.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+class RemovePatientSessionFromSessionAttendances < ActiveRecord::Migration[8.0]
+  def up
+    change_table :session_attendances, bulk: true do |t|
+      t.references :patient, foreign_key: true
+    end
+
+    SessionAttendance.find_each do |session_attendance|
+      patient_session =
+        PatientSession.find(session_attendance.patient_session_id)
+      patient_id = patient_session.patient_id
+      session_attendance.update_column(:patient_id, patient_id)
+    end
+
+    change_table :session_attendances, bulk: true do |t|
+      t.change_null :patient_id, false
+      t.remove_references :patient_session
+    end
+  end
+
+  def down
+    add_reference :session_attendances, :patient_session
+
+    SessionAttendance.find_each do |session_attendance|
+      session_id =
+        SessionDate.find(session_attendance.session_date_id).session_id
+      patient_session =
+        PatientSession.find_by!(
+          patient_id: session_attendance.patient_id,
+          session_id:
+        )
+      session_attendance.update_column(:patient_session_id, patient_session.id)
+    end
+
+    change_table :gillick_assessments, bulk: true do |t|
+      t.change_null :patient_session_id, false
+      t.remove_references :patient
+    end
+  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_08_21_124416) do
+ActiveRecord::Schema[8.0].define(version: 2025_08_21_135954) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_catalog.plpgsql"
   enable_extension "pg_trgm"
@@ -780,12 +780,12 @@
   end
 
   create_table "session_attendances", force: :cascade do |t|
-    t.bigint "patient_session_id", null: false
     t.bigint "session_date_id", null: false
     t.boolean "attending", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.index ["patient_session_id", "session_date_id"], name: "idx_on_patient_session_id_session_date_id_be8bd21ddf", unique: true
+    t.bigint "patient_id", null: false
+    t.index ["patient_id"], name: "index_session_attendances_on_patient_id"
     t.index ["session_date_id"], name: "index_session_attendances_on_session_date_id"
   end
 
@@ -1085,7 +1085,7 @@
   add_foreign_key "school_moves", "locations", column: "school_id"
   add_foreign_key "school_moves", "patients"
   add_foreign_key "school_moves", "teams"
-  add_foreign_key "session_attendances", "patient_sessions"
+  add_foreign_key "session_attendances", "patients"
   add_foreign_key "session_attendances", "session_dates"
   add_foreign_key "session_dates", "sessions"
   add_foreign_key "session_notifications", "patients"

spec/factories/patient_sessions.rb

@@ -52,16 +52,22 @@
     end
 
     trait :in_attendance do
-      session_attendances do
-        [association(:session_attendance, :present, patient_session: instance)]
-      end
       registration_status do
         association(
           :patient_session_registration_status,
           :attending,
           patient_session: instance
         )
       end
+
+      after(:create) do |patient_session|
+        create(
+          :session_attendance,
+          :present,
+          patient: patient_session.patient,
+          session: patient_session.session
+        )
+      end
     end
 
     trait :added_to_session