Friday, September 10, 2010

Deleted rows available in a transaction

I am facing a very peculiar problem that even when I delete some rows,
I can just get them back again in same transaction.

Edit:
I have created a sample app to test it out, so that I can be sure that
none of my code is culprit.

I created a testapp with following code

**models.py**

import uuid
from django.db import models

class TestTable(models.Model):
id = models.CharField(max_length=36, primary_key=True)
name = models.CharField(max_length=50)

@classmethod
def get_row(cls, name):
return TestTable(id=str(uuid.uuid4()), name=name)

def __unicode__(self):
return u"%s[%s]"%(self.name, self.id)

**views.py**

import traceback
import time
from django.db import transaction
from django.http import HttpResponse

from testapp.models import TestTable

@transaction.commit_manually
def test_view(request):
time.sleep(1)
out = []
try:
# delete 3 rows
for row in TestTable.objects.all()[:3]:
ID=row.id
out.append("deleting %s"%row)
row.delete()
# check fi really deleted
try:
TestTable.objects.get(id=ID)
out.append("row not deleted?")
except TestTable.DoesNotExist,e:
out.append("row deleted.")

# create 5 rows
for i in range(5):
row = TestTable.get_row("row %s"%i)
row.save()

except Exception,e:
out.append("Error:%s"%traceback.format_exc())
transaction.rollback()
else:
transaction.commit()

return HttpResponse('\n'.join(out), 'text/text'

**urls.py**

from django.conf.urls.defaults import *

urlpatterns = patterns('testapp.views', (r'^test_bug$',
'test_view')

I am running this under apache and mod_wsgi

**TestScript**

import urllib2
from multiprocessing import Process

def get_data():
r = urllib2.urlopen("http://localhost:81/timeapp/test/
test_bug")
print "---------"
print r.read()

if __name__ == "__main__":
for i in range(2):
p = Process(target=get_data)
p.start()

**Output:**

$ python test.py
---------
deleting row 1[3ad3a82e-830f-4540-8148-88479175ed5e]
row deleted.
deleting row 0[544462d1-8588-4a8c-a809-16a060054479]
row deleted.
deleting row 3[55d422f3-6c39-4c26-943a-1b4db498bf25]
row deleted.
---------
deleting row 1[3ad3a82e-830f-4540-8148-88479175ed5e]
row not deleted?
deleting row 0[544462d1-8588-4a8c-a809-16a060054479]
row not deleted?
deleting row 3[55d422f3-6c39-4c26-943a-1b4db498bf25]
row not deleted?

So my question is how come deleted row is again retrievable by
TestTable.objects.get, also even if I sleep more in second call so
that first call can commit code I still get deleted rows in second
call.

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