Make the database do the work

blossom/api/views/submission.py

@@ -6,11 +6,13 @@
 from typing import Union
 
 from django.conf import settings
-from django.db.models import Count, F
+from django.db.models import Count, F, Value
 from django.db.models.functions import (
     ExtractHour,
     ExtractIsoWeekDay,
     Length,
+    StrIndex,
+    Substr,
     TruncDate,
     TruncDay,
     TruncHour,
@@ -37,13 +39,7 @@
 
 from blossom.api.authentication import BlossomApiPermission
 from blossom.api.helpers import validate_request
-from blossom.api.models import (
-    Source,
-    Submission,
-    Transcription,
-    TranscriptionCheck,
-    extract_subreddit_from_url,
-)
+from blossom.api.models import Source, Submission, Transcription, TranscriptionCheck
 from blossom.api.pagination import StandardResultsSetPagination
 from blossom.api.serializers import SubmissionSerializer
 from blossom.api.slack import client as slack
@@ -404,19 +400,23 @@ def subreddits(self, request: Request) -> Response:
         """Count the submissions by subreddit."""
         subreddit_query = (
             self.filter_queryset(Submission.objects)
-            # Only include Reddit posts with the expected URL format
+            # https://reddit.com/r/testing/comments/12345/hi/
             .filter(url__startswith="https://reddit.com/r/")
-            # Return only the relevant values
-            .values("id", "url")
+            # testing/comments/12345/hi/
+            .annotate(subreddit=Substr("url", 22, 50))
+            # 8
+            .annotate(slash_index=StrIndex("subreddit", Value("/")))
+            # testing
+            .annotate(subreddit_name=Substr("subreddit", 1, F("slash_index") - 1))
+            .values("subreddit_name")
+            .annotate(Count("subreddit_name"))
         )
 
         subreddit_counts: dict[str, int] = dict()
 
-        # Count the number of submissions per subreddit
-        # TODO: Make this more efficient (at the database level)
+        # Make the query response a little prettier
         for item in subreddit_query:
-            subreddit = extract_subreddit_from_url(item["url"])
-            subreddit_counts[subreddit] = subreddit_counts.get(subreddit, 0) + 1
+            subreddit_counts[item["subreddit_name"]] = item["subreddit_name__count"]
 
         # Sort descending by submission count
         sorted_subreddits = OrderedDict(