parser: don't trigger database IntegrityErrors on duplicate coverletters

As we've done for the Patch and Comment models, this change prevents
database errors from duplicate CoverLetters.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Stephen Finucane <stephen@that.guru>
[stephenfin: Add release note]
(cherry picked from commit 55fb26b)

Author: jk-ozlabs

patchwork/parser.py

@@ -1250,7 +1250,10 @@ def parse_mail(mail, list_id=None):
                 SeriesReference.objects.create(
                     msgid=msgid, project=project, series=series)
 
-            try:
+            with transaction.atomic():
+                if CoverLetter.objects.filter(project=project, msgid=msgid):
+                    raise DuplicateMailError(msgid=msgid)
+
                 cover_letter = CoverLetter.objects.create(
                     msgid=msgid,
                     project=project,
@@ -1259,8 +1262,6 @@ def parse_mail(mail, list_id=None):
                     headers=headers,
                     submitter=author,
                     content=message)
-            except IntegrityError:
-                raise DuplicateMailError(msgid=msgid)
 
             logger.debug('Cover letter saved')
 

patchwork/tests/test_parser.py

@@ -23,6 +23,7 @@
 from patchwork.models import Patch
 from patchwork.models import Person
 from patchwork.models import State
+from patchwork.models import CoverLetter
 from patchwork.parser import clean_subject
 from patchwork.parser import get_or_create_author
 from patchwork.parser import find_patch_content as find_content
@@ -1180,3 +1181,12 @@ def test_duplicate_comment(self):
 
         self.assertEqual(Patch.objects.count(), 1)
         self.assertEqual(Comment.objects.count(), 1)
+
+    def test_duplicate_coverletter(self):
+        m = create_email('test', listid=self.listid, msgid='1@example.com')
+        del m['Subject']
+        m['Subject'] = '[PATCH 0/1] test cover letter'
+
+        self._test_duplicate_mail(m)
+
+        self.assertEqual(CoverLetter.objects.count(), 1)

releasenotes/notes/issue-358-7d664318a19385fa.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    The parser module now uses an atomic select-insert when creating new patch,
+    cover letter and comment entries. This prevents the integrity errors from
+    being logged in the DB logs.
+    (`#358 <https://github.com/getpatchwork/patchwork/issues/358>`__)