fix(dbapi): don't assume rowcount exists (backport #5139 to 1.8) (#5201)

Some database drivers (namely cassandra-driver) do not implement
rowcount on cursor objects and so the dbapi integration fails.

I have omitted a test as I believe that the code and inlined comment is
sufficient for preventing regressions. Another factor was that it is not
trivial to add a test case repro-ing the issue with django +
cassandra-driver.

(Aside, perhaps having a special `regression` test suite/environment
which can be easily configured to test different permutations of libary
and version would be a good addition for cases like this)

Author: Kyle-Verhoog

ddtrace/contrib/dbapi/__init__.py

@@ -155,7 +155,11 @@ def callproc(self, proc, *args):
         return self._trace_method(self.__wrapped__.callproc, self._self_datadog_name, proc, {}, False, proc, *args)
 
     def _set_post_execute_tags(self, span):
-        row_count = self.__wrapped__.rowcount
+        # rowcount is in the dbapi specification (https://peps.python.org/pep-0249/#rowcount)
+        # but some database drivers (cassandra-driver specifically) don't implement it.
+        row_count = getattr(self.__wrapped__, "rowcount", None)
+        if row_count is None:
+            return
         span.set_metric("db.rowcount", row_count)
         # Necessary for django integration backward compatibility. Django integration used to provide its own
         # implementation of the TracedCursor, which used to store the row count into a tag instead of

docs/spelling_wordlist.txt

@@ -159,6 +159,7 @@ resolvers
 repo
 respawn
 rq
+rowcount
 runnable
 runtime
 runtimes

releasenotes/notes/dbapi-rowcount-3cf18b68114a6cad.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    dbapi: The dbapi integration no longer assumes that a cursor object will
+      have a rowcount but not all database drivers implement rowcount.