id summary reporter owner description type status component version severity resolution keywords cc stage has_patch needs_docs needs_tests needs_better_patch easy ui_ux 21956 Inconsistent behaviour of Q objects Debanshu Kundu nobody "Suppose we have a contact model with following definition: {{{ class Contact(models.Model): name = models.CharField() company_uid = models.IntegerField(null=True, blank=True) }}} Consider following two queries: `Contact.objects.filter(~(Q(name='ABC') | Q(company_uid=5)))` `Contact.objects.filter(~Q(name='ABC') & ~Q(company_uid=5))` These queries are exactly the same, right? Just used DeMorgan's law i.e ""not (A or B)"" is the same as ""(not A) and (not B)"". But the generated SQL of these queries says something else: `SELECT ""profiles_contact"".""id"", ""profiles_contact"".""name"", ""profiles_contact"".""company_uid"" FROM ""profiles_contact"" WHERE NOT ((""profiles_contact"".""name"" = ABC OR ""profiles_contact"".""company_uid"" = 5 ))` `SELECT ""profiles_contact"".""id"", ""profiles_contact"".""name"", ""profiles_contact"".""company_uid"" FROM ""profiles_contact"" WHERE (NOT (""profiles_contact"".""name"" = ABC ) AND NOT ((""profiles_contact"".""company_uid"" = 5 AND ""profiles_contact"".""company_uid"" IS NOT NULL)))` (The desired query is the one with `IS NOT NULL` condition) This issue only exists till version 1.5, it has been fixed in Django-1.6. There is already a closed bug (https://code.djangoproject.com/ticket/21192) which was similar to this one. The bug was closed stating that the issue has been fixed in Django-1.6 and changes required to back-patch the fixes to 1.5 are just too big. But I believe this issue is more severe than the issue stated the that bug, as it is a more general case and should be back-patched to 1.5 and older version too." Bug closed Database layer (models, ORM) 1.5 Normal wontfix Unreviewed 0 0 0 0 0 0