Provide unified coursebook for similar lessons

aleksis/apps/alsijil/schema.py

@@ -233,9 +233,9 @@ class Query(graphene.ObjectType):
                 )  # FIXME: Queries shouldn't alter data
 
         return LessonDocumentation.objects.filter(
-            lesson_period_id__in=LessonPeriod.objects.filter(lesson_id=id).values_list(
-                "id", flat=True
-            )
+            lesson_period_id__in=LessonPeriod.objects.filter(
+                lesson__in=lesson.equal_lessons
+            ).values_list("id", flat=True)
         ).order_by(
             "-year", "-week", "-lesson_period__period__weekday", "-lesson_period__period__period"
         )