fix: Fix the N+1 query issue in EventProceduresController#index (#333)

* fix: Fix the N+1 query issue in EventProceduresController#index caused by repeated database queries in EventProcedures::BuildTotalAmountCents

* refactor: creates indexed hashes for O(1) search

Author: danielnottingham

app/operations/event_procedures/build_total_amount_cents.rb

@@ -23,29 +23,30 @@ def base_amount_cents
       cbhpm_procedure = find_cbhpm_procedure
       return 0 unless cbhpm_procedure
 
-      port_value = find_port_value(cbhpm_procedure)
-      return value_for_anesthetic_port_zero(event_procedure) unless port_value
+      port_value = find_port_value(cbhpm_procedure.anesthetic_port)
+      return value_for_anesthetic_port_zero unless port_value
 
       port_value.amount_cents.to_i
     end
 
-    def value_for_anesthetic_port_zero(event_procedure)
-      port = PortValue.find_by(cbhpm_id: event_procedure.cbhpm_id, anesthetic_port: ANESTHETIC_PORT_ZERO_AMOUNT)
-      port&.amount_cents.to_i
+    def value_for_anesthetic_port_zero
+      port_values_by_anesthetic_port[ANESTHETIC_PORT_ZERO_AMOUNT]&.amount_cents.to_i
     end
 
     def find_cbhpm_procedure
-      CbhpmProcedure.find_by(
-        procedure_id: event_procedure.procedure_id,
-        cbhpm_id: event_procedure.cbhpm_id
-      )
+      cbhpm_procedures_by_cbhpm_id[event_procedure.cbhpm_id]
     end
 
-    def find_port_value(cbhpm_procedure)
-      PortValue.find_by(
-        cbhpm_id: cbhpm_procedure.cbhpm_id,
-        anesthetic_port: cbhpm_procedure.anesthetic_port
-      )
+    def find_port_value(anesthetic_port)
+      port_values_by_anesthetic_port[anesthetic_port]
+    end
+
+    def cbhpm_procedures_by_cbhpm_id
+      @cbhpm_procedures_by_cbhpm_id ||= event_procedure.procedure.cbhpm_procedures.index_by(&:cbhpm_id)
+    end
+
+    def port_values_by_anesthetic_port
+      @port_values_by_anesthetic_port ||= event_procedure.cbhpm.port_values.index_by(&:anesthetic_port)
     end
 
     def apartment_multiplier

app/operations/event_procedures/list.rb

@@ -21,7 +21,8 @@ def filtered_query
         :patient,
         :hospital,
         :health_insurance,
-        cbhpm: :port_values
+        cbhpm: :port_values,
+        procedure: :cbhpm_procedures
       )
       apply_all_filters(query)
     end

spec/requests/api/v1/event_procedures_request_spec.rb

@@ -28,6 +28,21 @@
       end
     end
 
+    context "when checking for N+1 queries" do
+      it "does not have N+1 queries" do
+        create_list(:event_procedure, 2, user_id: user.id)
+        get(path, params: {}, headers: headers) # Warmup
+
+        control_count = count_queries { get(path, params: {}, headers: headers) }
+
+        create_list(:event_procedure, 5, user_id: user.id)
+
+        final_count = count_queries { get(path, params: {}, headers: headers) }
+
+        expect(final_count).to be <= control_count
+      end
+    end
+
     context "when has filters by month" do
       it "returns event_procedures per month" do
         create_list(:event_procedure, 3, date: "2023-02-15", user_id: user.id)

spec/support/query_counter.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module QueryCounter
+  def count_queries(&)
+    count = 0
+    counter_f = lambda { |_name, _started, _finished, _unique_id, payload|
+      count += 1 unless payload[:name].in? %w[CACHE SCHEMA]
+    }
+    ActiveSupport::Notifications.subscribed(counter_f, "sql.active_record", &)
+    count
+  end
+end
+
+RSpec.configure do |config|
+  config.include QueryCounter, type: :request
+end