models: Use database constraints to prevent split Series

Currently, the 'SeriesReference' object has a unique constraint on the
two fields it has, 'series', which is a foreign key to 'Series', and
'msgid'. This is the wrong constraint. What we actually want to enforce
is that a patch, cover letter or comment is referenced by a single
series, or rather a single series per project the submission appears on.
As such, we should be enforcing uniqueness on the msgid and the project
that the patch, cover letter or comment belongs to.

This requires adding a new field to the object, 'project', since it's
not possible to do something like the following:

  unique_together = [('msgid', 'series__project')]

This is detailed here [1]. In addition, the migration needs a precursor
migration step to merge any broken series.

[1] https://stackoverflow.com/a/4440189/613428

Signed-off-by: Stephen Finucane <stephen@that.guru>
Closes: #241
Cc: Daniel Axtens <dja@axtens.net>
Cc: Petr Vorel <petr.vorel@gmail.com>

5 files changed, 199 insertions, 66 deletions

diff --git a/patchwork/migrations/0039_unique_series_references.py b/patchwork/migrations/0039_unique_series_references.py
new file mode 100644
index 0000000..99b10fc
--- /dev/null
+++ b/patchwork/migrations/0039_unique_series_references.py
@@ -0,0 +1,121 @@
+from django.db import connection, migrations, models
+from django.db.models import Count
+import django.db.models.deletion
+
+
+def merge_duplicate_series(apps, schema_editor):
+    SeriesReference = apps.get_model('patchwork', 'SeriesReference')
+    Patch = apps.get_model('patchwork', 'Patch')
+
+    msgid_seriesrefs = {}
+
+    # find all SeriesReference that share a msgid but point to different series
+    # and decide which of the series is going to be the authoritative one
+    msgid_counts = (
+        SeriesReference.objects.values('msgid')
+        .annotate(count=Count('msgid'))
+        .filter(count__gt=1)
+    )
+    for msgid_count in msgid_counts:
+        msgid = msgid_count['msgid']
+        chosen_ref = None
+        for series_ref in SeriesReference.objects.filter(msgid=msgid):
+            if series_ref.series.cover_letter:
+                if chosen_ref:
+                    # I don't think this can happen, but explode if it does
+                    raise Exception(
+                        "Looks like you've got two or more series that share "
+                        "some patches but do not share a cover letter. Unable "
+                        "to auto-resolve."
+                    )
+
+                # if a series has a cover letter, that's the one we'll group
+                # everything under
+                chosen_ref = series_ref
+
+        if not chosen_ref:
+            # if none of the series have cover letters, simply use the last
+            # one (hint: this relies on Python's weird scoping for for loops
+            # where 'series_ref' is still accessible outside the loop)
+            chosen_ref = series_ref
+
+        msgid_seriesrefs[msgid] = chosen_ref
+
+    # reassign any patches referring to non-authoritative series to point to
+    # the authoritative one, and delete the other series; we do this separately
+    # to allow us a chance to raise the exception above if necessary
+    for msgid, chosen_ref in msgid_seriesrefs.items():
+        for series_ref in SeriesReference.objects.filter(msgid=msgid):
+            if series_ref == chosen_ref:
+                continue
+
+            # update the patches to point to our chosen series instead, on the
+            # assumption that all other metadata is correct
+            for patch in Patch.objects.filter(series=series_ref.series):
+                patch.series = chosen_ref.series
+                patch.save()
+
+            # delete the other series (which will delete the series ref)
+            series_ref.series.delete()
+
+
+def copy_project_field(apps, schema_editor):
+    if connection.vendor == 'postgresql':
+        schema_editor.execute(
+            """
+            UPDATE patchwork_seriesreference
+              SET project_id = patchwork_series.project_id
+            FROM patchwork_series
+              WHERE patchwork_seriesreference.series_id = patchwork_series.id
+        """
+        )
+    elif connection.vendor == 'mysql':
+        schema_editor.execute(
+            """
+            UPDATE patchwork_seriesreference, patchwork_series
+              SET patchwork_seriesreference.project_id = patchwork_series.project_id
+            WHERE patchwork_seriesreference.series_id = patchwork_series.id
+        """  # noqa
+        )
+    else:
+        SeriesReference = apps.get_model('patchwork', 'SeriesReference')
+
+        for series_ref in SeriesReference.objects.all().select_related(
+            'series'
+        ):
+            series_ref.project = series_ref.series.project
+            series_ref.save()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [('patchwork', '0038_state_slug')]
+
+    operations = [
+        migrations.RunPython(
+            merge_duplicate_series, migrations.RunPython.noop, atomic=False
+        ),
+        migrations.AddField(
+            model_name='seriesreference',
+            name='project',
+            field=models.ForeignKey(
+                null=True,
+                on_delete=django.db.models.deletion.CASCADE,
+                to='patchwork.Project',
+            ),
+        ),
+        migrations.AlterUniqueTogether(
+            name='seriesreference', unique_together={('project', 'msgid')}
+        ),
+        migrations.RunPython(
+            copy_project_field, migrations.RunPython.noop, atomic=False
+        ),
+        migrations.AlterField(
+            model_name='seriesreference',
+            name='project',
+            field=models.ForeignKey(
+                on_delete=django.db.models.deletion.CASCADE,
+                to='patchwork.Project',
+            ),
+        ),
+    ]
diff --git a/patchwork/models.py b/patchwork/models.py
index d95eb0d..be71d40 100644
--- a/patchwork/models.py
+++ b/patchwork/models.py
@@ -79,7 +79,8 @@ class Project(models.Model):
     webscm_url = models.CharField(max_length=2000, blank=True)
     list_archive_url = models.CharField(max_length=2000, blank=True)
     list_archive_url_format = models.CharField(
-        max_length=2000, blank=True,
+        max_length=2000,
+        blank=True,
         help_text="URL format for the list archive's Message-ID redirector. "
         "{} will be replaced by the Message-ID.")
     commit_url_format = models.CharField(
@@ -785,6 +786,7 @@ class SeriesReference(models.Model):
     required to handle the case whereby one or more patches are
     received before the cover letter.
     """
+    project = models.ForeignKey(Project, on_delete=models.CASCADE)
     series = models.ForeignKey(Series, related_name='references',
                                related_query_name='reference',
                                on_delete=models.CASCADE)
@@ -794,7 +796,7 @@ class SeriesReference(models.Model):
         return self.msgid
 
     class Meta:
-        unique_together = [('series', 'msgid')]
+        unique_together = [('project', 'msgid')]
 
 
 class Bundle(models.Model):
diff --git a/patchwork/parser.py b/patchwork/parser.py
index c424729..c0084cc 100644
--- a/patchwork/parser.py
+++ b/patchwork/parser.py
@@ -16,6 +16,7 @@ import re
 
 from django.contrib.auth.models import User
 from django.db.utils import IntegrityError
+from django.db import transaction
 from django.utils import six
 
 from patchwork.models import Comment
@@ -256,16 +257,9 @@ def _find_series_by_references(project, mail):
     for ref in refs:
         try:
             return SeriesReference.objects.get(
-                msgid=ref[:255], series__project=project).series
+                msgid=ref[:255], project=project).series
         except SeriesReference.DoesNotExist:
             continue
-        except SeriesReference.MultipleObjectsReturned:
-            # FIXME: Open bug: this can happen when we're processing
-            # messages in parallel. Pick the first and log.
-            logger.error("Multiple SeriesReferences for %s in project %s!" %
-                         (ref[:255], project.name))
-            return SeriesReference.objects.filter(
-                msgid=ref[:255], series__project=project).first().series
 
 
 def _find_series_by_markers(project, mail, author):
@@ -1092,47 +1086,65 @@ def parse_mail(mail, list_id=None):
         except IntegrityError:
             raise DuplicateMailError(msgid=msgid)
 
-        # if we don't have a series marker, we will never have an existing
-        # series to match against.
-        series = None
-        if n:
-            series = find_series(project, mail, author)
+        for attempt in range(1, 11):  # arbitrary retry count
+            try:
+                with transaction.atomic():
+                    # if we don't have a series marker, we will never have an
+                    # existing series to match against.
+                    series = None
+                    if n:
+                        series = find_series(project, mail, author)
+                    else:
+                        x = n = 1
+
+                    # We will create a new series if:
+                    # - there is no existing series to assign this patch to, or
+                    # - there is an existing series, but it already has a patch
+                    #   with this number in it
+                    if not series or Patch.objects.filter(
+                            series=series, number=x).count():
+                        series = Series.objects.create(
+                            project=project,
+                            date=date,
+                            submitter=author,
+                            version=version,
+                            total=n)
+
+                        # NOTE(stephenfin) We must save references for series.
+                        # We do this to handle the case where a later patch is
+                        # received first. Without storing references, it would
+                        # not be possible to identify the relationship between
+                        # patches as the earlier patch does not reference the
+                        # later one.
+                        for ref in refs + [msgid]:
+                            ref = ref[:255]
+                            # we don't want duplicates
+                            try:
+                                # we could have a ref to a previous series.
+                                # (For example, a series sent in reply to
+                                # another series.) That should not create a
+                                # series ref for this series, so check for the
+                                # msg-id only, not the msg-id/series pair.
+                                SeriesReference.objects.get(
+                                    msgid=ref, project=project)
+                            except SeriesReference.DoesNotExist:
+                                SeriesReference.objects.create(
+                                    msgid=ref, project=project, series=series)
+                    break
+            except IntegrityError:
+                # we lost the race so go again
+                logger.warning('Conflict while saving series. This is '
+                               'probably because multiple patches belonging '
+                               'to the same series have been received at '
+                               'once. Trying again (attempt %02d/10)',
+                               attempt)
         else:
-            x = n = 1
-
-        # We will create a new series if:
-        # - there is no existing series to assign this patch to, or
-        # - there is an existing series, but it already has a patch with this
-        #   number in it
-        if not series or Patch.objects.filter(series=series, number=x).count():
-            series = Series.objects.create(
-                project=project,
-                date=date,
-                submitter=author,
-                version=version,
-                total=n)
-
-            # NOTE(stephenfin) We must save references for series. We
-            # do this to handle the case where a later patch is
-            # received first. Without storing references, it would not
-            # be possible to identify the relationship between patches
-            # as the earlier patch does not reference the later one.
-            for ref in refs + [msgid]:
-                ref = ref[:255]
-                # we don't want duplicates
-                try:
-                    # we could have a ref to a previous series. (For
-                    # example, a series sent in reply to another
-                    # series.) That should not create a series ref
-                    # for this series, so check for the msg-id only,
-                    # not the msg-id/series pair.
-                    SeriesReference.objects.get(msgid=ref,
-                                                series__project=project)
-                except SeriesReference.DoesNotExist:
-                    SeriesReference.objects.create(series=series, msgid=ref)
-                except SeriesReference.MultipleObjectsReturned:
-                    logger.error("Multiple SeriesReferences for %s"
-                                 " in project %s!" % (ref, project.name))
+            # we failed to save the series so return the series-less patch
+            logger.warning('Failed to save series. Your patch with message ID '
+                           '%s has been saved but this should not happen. '
+                           'Please report this as a bug and include logs',
+                           msgid)
+            return patch
 
         # add to a series if we have found one, and we have a numbered
         # patch. Don't add unnumbered patches (for example diffs sent
@@ -1170,14 +1182,9 @@ def parse_mail(mail, list_id=None):
             # message
             try:
                 series = SeriesReference.objects.get(
-                    msgid=msgid, series__project=project).series
+                    msgid=msgid, project=project).series
             except SeriesReference.DoesNotExist:
                 series = None
-            except SeriesReference.MultipleObjectsReturned:
-                logger.error("Multiple SeriesReferences for %s"
-                             " in project %s!" % (msgid, project.name))
-                series = SeriesReference.objects.filter(
-                    msgid=msgid, series__project=project).first().series
 
             if not series:
                 series = Series.objects.create(
@@ -1190,12 +1197,8 @@ def parse_mail(mail, list_id=None):
                 # we don't save the in-reply-to or references fields
                 # for a cover letter, as they can't refer to the same
                 # series
-                try:
-                    SeriesReference.objects.get_or_create(series=series,
-                                                          msgid=msgid)
-                except SeriesReference.MultipleObjectsReturned:
-                    logger.error("Multiple SeriesReferences for %s"
-                                 " in project %s!" % (msgid, project.name))
+                SeriesReference.objects.create(
+                    msgid=msgid, project=project, series=series)
 
             try:
                 cover_letter = CoverLetter.objects.create(
diff --git a/patchwork/tests/test_parser.py b/patchwork/tests/test_parser.py
index 0bf7158..0edbd87 100644
--- a/patchwork/tests/test_parser.py
+++ b/patchwork/tests/test_parser.py
@@ -421,17 +421,20 @@ class SeriesCorrelationTest(TestCase):
         msgids = [make_msgid()]
         project = create_project()
         series_v1 = create_series(project=project)
-        create_series_reference(msgid=msgids[0], series=series_v1)
+        create_series_reference(msgid=msgids[0], series=series_v1,
+                                project=project)
 
         # ...and three patches
         for i in range(3):
             msgids.append(make_msgid())
-            create_series_reference(msgid=msgids[-1], series=series_v1)
+            create_series_reference(msgid=msgids[-1], series=series_v1,
+                                    project=project)
 
         # now create a new series with "cover letter"
         msgids.append(make_msgid())
         series_v2 = create_series(project=project)
-        ref_v2 = create_series_reference(msgid=msgids[-1], series=series_v2)
+        ref_v2 = create_series_reference(msgid=msgids[-1], series=series_v2,
+                                         project=project)
 
         # ...and the "first patch" of this new series
         msgid = make_msgid()
diff --git a/patchwork/tests/utils.py b/patchwork/tests/utils.py
index 91bcbe1..5e6a1b1 100644
--- a/patchwork/tests/utils.py
+++ b/patchwork/tests/utils.py
@@ -283,8 +283,12 @@ def create_series(**kwargs):
 
 def create_series_reference(**kwargs):
     """Create 'SeriesReference' object."""
+    project = kwargs.pop('project', create_project())
+    series = kwargs.pop('series', create_series(project=project))
+
     values = {
-        'series': create_series() if 'series' not in kwargs else None,
+        'series': series,
+        'project': project,
         'msgid': make_msgid(),
     }
     values.update(**kwargs)