Django: executing UPDATE query always returns rowcount 0 - sql-server

Question

I'm new to programming and I'm not sure, whether the problem is in me or in the Django code. I call link method from my view and update field MatchId on Record model. Database is SQL Server 2017.
My view:
class RecordViewSet(viewsets.ModelViewSet):
"""
API for everything that has to do with Records.
Additionally we provide an extra `link` action.
"""
queryset = Record.objects.all().order_by("Id")
serializer_class = RecordSerializer
permission_classes = [permissions.IsAuthenticated]
#action(methods=["post"], detail=False)
def link(self, request, *args, **kwargs):
idToMatch = request.POST.getlist("Id")
recordsToMatch = Record.objects.filter(Id__in=idToMatch)
lastMatchId = Record.objects.latest("MatchId").MatchId
matchedSuccesfully = recordsToMatch.update(MatchId=lastMatchId + 1)
if matchedSuccesfully > 1:
return Response(data=matchedSuccesfully, status=status.HTTP_200_OK)
else:
return Response(data=matchedSuccesfully, status=status.HTTP_404_NOT_FOUND)
For some reason matchedSuccessfully always returns zero. Relevant Django code:
def execute_sql(self, result_type):
"""
Execute the specified update. Return the number of rows affected by
the primary update query. The "primary update query" is the first
non-empty query that is executed. Row counts for any subsequent,
related queries are not available.
"""
cursor = super().execute_sql(result_type)
try:
rows = cursor.rowcount if cursor else 0
is_empty = cursor is None
finally:
if cursor:
cursor.close()
for query in self.query.get_related_updates():
aux_rows = query.get_compiler(self.using).execute_sql(result_type)
if is_empty and aux_rows:
rows = aux_rows
is_empty = False
return rows
I rewrote execute_sql as follows:
def execute_sql(self, result_type):
"""
Execute the specified update. Return the number of rows affected by
the primary update query. The "primary update query" is the first
non-empty query that is executed. Row counts for any subsequent,
related queries are not available.
"""
cursor = super().execute_sql(result_type)
try:
if cursor:
cursor.execute("select ##rowcount")
rows = cursor.fetchall()[0][0]
else:
rows = 0
is_empty = cursor is None
finally:
if cursor:
cursor.close()
for query in self.query.get_related_updates():
aux_rows = query.get_compiler(self.using).execute_sql(result_type)
if is_empty and aux_rows:
rows = aux_rows
is_empty = False
return rows
and now it works, but I'm unsure if there is a more elegant way to resolve this since now I have to ship this exact code everywhere. Source code at:
https://github.com/django/django/blob/main/django/db/models/sql/compiler.py

Answer 1

I've faced the same issue and came to the same point in django's depths.
In my case — the problem was in trigger configured for UPDATE.
It should have return ##ROWCOUNT as a result, but in my case it didn't.
Btw, the thing I did (due to restriction on editing triggers) — overrided save method in base model for such models to force_update=True:
class BaseModel(models.Model):
def save(self, force_insert=False, force_update=False, using=None, update_fields=None):
if self._state.adding:
super().save(force_insert=force_insert, force_update=force_update, using=using, update_fields=update_fields)
else:
try:
super().save(force_insert=force_insert, force_update=True, using=using, update_fields=update_fields)
except DatabaseError as e:
if str(e) == 'Forced update did not affect any rows.':
pass
else:
raise e
class Meta:
managed = False
abstract = True