Create RecommendedWorkerVersionRetrieve endpoint

closes #1888 (closed)

arkindex/process/api.py

@@ -1180,12 +1180,14 @@ class RecommendedWorkerVersionRetrieve(RetrieveAPIView):
             # tag_as_int is created by splitting on an eventual '-' so if we have '0.3.2' and '0.3.2-rc2' they both have 32
             # as `tag_as_int`. The second ordering by tag (regular alphabetical ordering) ensures that the main version (0.3.2)
             # is returned in this case.
+            # The concatenation of a 0 at the beginning of each tag_as_int ensures that the casting to integer will always work,
+            # even if after applying the regex we end up with an empty string.
             # This will not order such version tags satisfactorily if the '-rc{number}' part goes beyond 9, as this is
             # alphabetical ordering so 1 > 10 > 2 > 3 > 4 etc.
             return (
                 self.worker.versions.filter(tag__isnull=False)
                 .filter(state=WorkerVersionState.Available) \
-                .annotate(tag_as_int=RawSQL("split_part(regexp_replace(tag, '[^0-9-]', '', 'g'), '-', 1)::int", []))
+                .annotate(tag_as_int=RawSQL("concat('0', split_part(regexp_replace(tag, '[^0-9-]', '', 'g'), '-', 1))::int", []))
                 .using("default") \
                 .select_related("worker__type") \
                 .distinct() \