Try matching against all four values first

This should improve the reliability of repeated cohort uploads by
ensuring twins and other scenarios where three of the four datapoints
match and don't result in a validation error for multiple matches.

Author: thomasleese

app/models/patient.rb

@@ -172,41 +172,61 @@ def self.match_existing(
     end
 
     scope =
-      Patient
-        .where(
-          "given_name ILIKE ? AND family_name ILIKE ?",
-          given_name,
-          family_name
-        )
-        .where(date_of_birth:)
-        .or(
-          Patient.where(
-            "given_name ILIKE ? AND family_name ILIKE ?",
-            given_name,
-            family_name
-          ).where(address_postcode:)
-        )
-        .or(
-          Patient.where("given_name ILIKE ?", given_name).where(
-            date_of_birth:,
-            address_postcode:
+      Patient.where(
+        "given_name ILIKE ? AND family_name ILIKE ?",
+        given_name,
+        family_name
+      ).where(date_of_birth:)
+
+    if address_postcode.present?
+      scope =
+        scope
+          .or(
+            Patient.where(
+              "given_name ILIKE ? AND family_name ILIKE ?",
+              given_name,
+              family_name
+            ).where(address_postcode:)
           )
-        )
-        .or(
-          Patient.where("family_name ILIKE ?", family_name).where(
-            date_of_birth:,
-            address_postcode:
+          .or(
+            Patient.where("given_name ILIKE ?", given_name).where(
+              date_of_birth:,
+              address_postcode:
+            )
+          )
+          .or(
+            Patient.where("family_name ILIKE ?", family_name).where(
+              date_of_birth:,
+              address_postcode:
+            )
           )
-        )
+    end
 
-    if nhs_number.blank?
-      scope.to_a
-    else
-      # This prevents us from finding a patient that happens to have at least
-      # three of the other fields the same, but with a different NHS number,
-      # and therefore cannot be a match.
-      Patient.where(nhs_number: nil).merge(scope).to_a
+    results =
+      if nhs_number.blank?
+        scope.to_a
+      else
+        # This prevents us from finding a patient that happens to have at least
+        # three of the other fields the same, but with a different NHS number,
+        # and therefore cannot be a match.
+        Patient.where(nhs_number: nil).merge(scope).to_a
+      end
+
+    if address_postcode.present?
+      # Check for an exact match of all four datapoints, we do this in memory
+      # to avoid an extra query to the database for each record.
+      exact_results =
+        results.select do
+          _1.given_name.downcase == given_name.downcase &&
+            _1.family_name.downcase == family_name.downcase &&
+            _1.date_of_birth == date_of_birth &&
+            _1.address_postcode == UKPostcode.parse(address_postcode).to_s
+        end
+
+      return exact_results if exact_results.length == 1
     end
+
+    results
   end
 
   def relationship_to(parent:)

spec/models/patient_spec.rb

@@ -160,7 +160,9 @@
     context "with matching first name, last name and postcode not provided" do
       let(:nhs_number) { nil }
       let(:address_postcode) { nil }
-      let(:patient) { create(:patient, given_name:, family_name:) }
+      let(:patient) do
+        create(:patient, given_name:, family_name:, address_postcode: nil)
+      end
 
       it { should_not include(patient) }
     end