add support for fulfilling with 3 digit codes/other courses in topic

backend/degree/serializers.py

@@ -1,6 +1,6 @@
 from textwrap import dedent
 
-from django.db.models import Q
+from django.db.models import Q, Subquery
 from rest_framework import serializers
 
 from courses.models import Course
@@ -143,13 +143,19 @@ def validate(self, data):
         for rule in rules:
             # NOTE: we don't do any validation if the course doesn't exist in DB. In future,
             # it may be better to prompt user for manual override
-            if (
-                Course.objects.filter(full_code=full_code).exists()
-                and not Course.objects.filter(rule.get_q_object(), full_code=full_code).exists()
-            ):
-                raise serializers.ValidationError(
-                    f"Course {full_code} does not satisfy rule {rule.id}"
-                )
+            if (Course.objects.filter(full_code=full_code).exists()):
+                satisfying_courses = Course.objects.filter(rule.get_q_object())
+                if (
+                    not (
+                        Course.objects.filter(
+                            full_code=full_code,
+                            topic_id__in=Subquery(satisfying_courses.values('topic_id'))
+                        ).exists()
+                    )
+                ):
+                    raise serializers.ValidationError(
+                        f"Course {full_code} does not satisfy rule {rule.id}"
+                    )
 
         # Check for double count restrictions
         double_count_restrictions = DoubleCountRestriction.objects.filter(