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Does django deleted row exist?

I had a very strange problem: even when I delete several lines, I can simply return them back to one transaction. I run this under apache and mod_wsgi, the database is mysql.

Edit: I created an example application to test it, so that I can be sure that none of my codes are the culprit.

I created testapp with the 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')

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()

Conclusion:

$ 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 why the deleted line is restored again with TestTable.objects.get, even if I sleep more in the second call so that the first call can make the code, I still get the deleted lines in the second call.

+3
4

, , , , , python-MySQL, MySQL. :

, , :

try:
    TestTable.objects.get(id=ID)
    out.append("row not deleted?")
except TestTable.DoesNotExist,e:
    out.append("row deleted.")

:

c = TestTable.objects.filter(id=ID).count()
if c:
    out.append("row not deleted?")
else:
    out.append("row deleted.")

.

-, Django . , MySQL (1 2 , ):

1 Query SET NAMES utf8
2 Query SET NAMES utf8
2 Query set autocommit=0
1 Query set autocommit=0
1 Query SELECT `testapp_testtable`.`id`, `testapp_testtable`.`name` FROM `testapp_testtable` LIMIT 3
2 Query SELECT `testapp_testtable`.`id`, `testapp_testtable`.`name` FROM `testapp_testtable` LIMIT 3
2 Query DELETE FROM `testapp_testtable` WHERE `id` IN ('32f027ff-c798-410b-8621-c2d47e2cfa7c')
1 Query DELETE FROM `testapp_testtable` WHERE `id` IN ('32f027ff-c798-410b-8621-c2d47e2cfa7c')
2 Query SELECT COUNT(*) FROM `testapp_testtable` WHERE `testapp_testtable`.`id` = '32f027ff-c798-410b-8621-c2d47e2cfa7c'
2 Query DELETE FROM `testapp_testtable` WHERE `id` IN ('3f693297-9993-4162-98c4-a9ca68232c75')
2 Query SELECT COUNT(*) FROM `testapp_testtable` WHERE `testapp_testtable`.`id` = '3f693297-9993-4162-98c4-a9ca68232c75'
2 Query DELETE FROM `testapp_testtable` WHERE `id` IN ('96f9a1f7-c818-4528-858f-4e85a93de5c3')
2 Query SELECT COUNT(*) FROM `testapp_testtable` WHERE `testapp_testtable`.`id` = '96f9a1f7-c818-4528-858f-4e85a93de5c3'
2 Query SELECT (1) AS `a` FROM `testapp_testtable` WHERE `testapp_testtable`.`id` = '035c90ba-82a6-4bdc-afe1-318382563017'  LIMIT 1
2 Query INSERT INTO `testapp_testtable` (`id`, `name`) VALUES ('035c90ba-82a6-4bdc-afe1-318382563017', 'row 0')
2 Query SELECT (1) AS `a` FROM `testapp_testtable` WHERE `testapp_testtable`.`id` = '15393978-4200-4b98-98e6-73636c39dd1c'  LIMIT 1
2 Query INSERT INTO `testapp_testtable` (`id`, `name`) VALUES ('15393978-4200-4b98-98e6-73636c39dd1c', 'row 1')
2 Query SELECT (1) AS `a` FROM `testapp_testtable` WHERE `testapp_testtable`.`id` = '22459ba2-18d5-4175-ac6b-2377ba63ecc7'  LIMIT 1
2 Query INSERT INTO `testapp_testtable` (`id`, `name`) VALUES ('22459ba2-18d5-4175-ac6b-2377ba63ecc7', 'row 2')
2 Query commit
2 Quit  
1 Query SELECT COUNT(*) FROM `testapp_testtable` WHERE `testapp_testtable`.`id` = '32f027ff-c798-410b-8621-c2d47e2cfa7c'
1 Query DELETE FROM `testapp_testtable` WHERE `id` IN ('3f693297-9993-4162-98c4-a9ca68232c75')
1 Query SELECT COUNT(*) FROM `testapp_testtable` WHERE `testapp_testtable`.`id` = '3f693297-9993-4162-98c4-a9ca68232c75'
1 Query DELETE FROM `testapp_testtable` WHERE `id` IN ('96f9a1f7-c818-4528-858f-4e85a93de5c3')
1 Query SELECT COUNT(*) FROM `testapp_testtable` WHERE `testapp_testtable`.`id` = '96f9a1f7-c818-4528-858f-4e85a93de5c3'
1 Query SELECT (1) AS `a` FROM `testapp_testtable` WHERE `testapp_testtable`.`id` = '6dc6e901-bebe-4f3b-98d1-c8c4a90d06df'  LIMIT 1
1 Query INSERT INTO `testapp_testtable` (`id`, `name`) VALUES ('6dc6e901-bebe-4f3b-98d1-c8c4a90d06df', 'row 0')
1 Query SELECT (1) AS `a` FROM `testapp_testtable` WHERE `testapp_testtable`.`id` = 'c335ccad-31c6-4ddd-bccd-578435cd6e7b'  LIMIT 1
1 Query INSERT INTO `testapp_testtable` (`id`, `name`) VALUES ('c335ccad-31c6-4ddd-bccd-578435cd6e7b', 'row 1')
1 Query SELECT (1) AS `a` FROM `testapp_testtable` WHERE `testapp_testtable`.`id` = '2c507629-a87e-48ec-b80d-2f758cd16c44'  LIMIT 1
1 Query INSERT INTO `testapp_testtable` (`id`, `name`) VALUES ('2c507629-a87e-48ec-b80d-2f758cd16c44', 'row 2')
1 Query commit
1 Quit

, , , , . , SQL django.db.models.sql.query , SELECT COUNT, DELETE , 1, 0. .

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  • Apache conf MaxClients ThreadsPerChild 1 ( ).
  • PostgreSQL ( , MySQL).
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You can also try adding some timestamps and a dump of used sql. Set DEBUG = True to settings.py, and then can look at your raw SQL queries .

# views.py
from django.db import connection

def test_view(request):
    connection.queries = []
    start_time = time.time()
    out = []
    out.append("%09.6f" % (time.time() % 100))  # something like 13.45678
    time.sleep(1)
    [...]
        # delete 3 rows
            [...]
            out.append("deleting %s"%row)
            out.append("%09.6f" % (time.time() % 100))
            [...]
            out.append("%d queries after the last delete" %d len(connection.queries))
        # create 5 rows
    [...]
    out.append("%09.6f total time spent" % (time.time() - start_time))
    out.append("%d queries TOTAL" %d len(connection.queries))
    # dump the actual queries if you are still digging.
    for q in connection.queries:
        out.append("%s\n----" % q)
0
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Source: https://habr.com/ru/post/1764108/

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