title: django.db OperationalError Example Code
category: page
slug: django-db-operationalerror-examples
sortorder: 500012920
toc: False
sidebartitle: django.db OperationalError
meta: Python code examples for the OperationalError exception class that is part of Django web framework's django.db package.


[OperationalError](https://github.com/django/django/blob/master/django/db/utils.py)
([documentation](https://docs.djangoproject.com/en/stable/ref/exceptions/#django.db.OperationalError))
is one of many possible 
[Python exceptions](https://docs.python.org/3/tutorial/errors.html)
thrown by the [Django](/django.html) [web framework](/web-frameworks.html)
when there is an issue that occurs in the [Django ORM](/django-orm.html).

Note that OperationalError can be imported either from `django.db` 
or `django.db.utils`.


## Example 1 from django-cms
[django-cms](https://github.com/divio/django-cms)
([project website](https://www.django-cms.org/en/)) is a Python-based
content management system (CMS) [library](https://pypi.org/project/django-cms/)
for use with Django web apps that is open sourced under the
[BSD 3-Clause "New"](https://github.com/divio/django-cms/blob/develop/LICENSE)
license.

[**django-cms / cms/admin / permissionadmin.py**](https://github.com/divio/django-cms/blob/develop/cms/admin/permissionadmin.py)

```python
# -*- coding: utf-8 -*-
from copy import deepcopy

from django.contrib import admin
from django.contrib.admin import site
from django.contrib.auth import get_user_model
from django.contrib.auth.admin import UserAdmin
from django.contrib.sites.models import Site
~~from django.db import OperationalError
from django.utils.translation import gettext_lazy as _

from cms.admin.forms import (GlobalPagePermissionAdminForm, 
                             PagePermissionInlineAdminForm, 
                             ViewRestrictionInlineAdminForm)
from cms.exceptions import NoPermissionsException
from cms.models import PagePermission, GlobalPagePermission
from cms.utils import permissions, page_permissions
from cms.utils.conf import get_cms_setting
from cms.utils.helpers import classproperty


PERMISSION_ADMIN_INLINES = []

user_model = get_user_model()
admin_class = UserAdmin
for model, admin_instance in site._registry.items():
    if model == user_model:
        admin_class = admin_instance.__class__


class TabularInline(admin.TabularInline):
    pass


class PagePermissionInlineAdmin(TabularInline):
    model = PagePermission
    # use special form, so we can override of user and group field
    form = PagePermissionInlineAdminForm
    classes = ['collapse', 'collapsed']
    extra = 0  # edit page load time boost
    show_with_view_permissions = False

    def has_change_permission(self, request, obj=None):
        if not obj:
            return False
        return page_permissions.user_can_change_page_permissions(
            request.user,
            page=obj,
            site=obj.node.site,
        )

    def has_add_permission(self, request, obj=None):
        return self.has_change_permission(request, obj)

    @classproperty
    def raw_id_fields(cls):
        # Dynamically set raw_id_fields based on settings
        threshold = get_cms_setting('RAW_ID_USERS')

        # Given a fresh django-cms install and a django settings 
        # with the CMS_RAW_ID_USERS = CMS_PERMISSION = True
        # django throws an OperationalError when running
        # ./manage migrate
        # because auth_user doesn't exists yet
~~        try:
~~            threshold = threshold and \
                get_user_model().objects.count() > threshold
~~        except OperationalError:
~~            threshold = False

        return ['user'] if threshold else []

    def get_queryset(self, request):
        """
        Queryset change, so user with global change permissions can 
        see all permissions. Otherwise user can see only permissions 
        for peoples which are under him (he can't see his permissions, 
        because this will lead to violation, when he can add more 
        power to himself)
        """
        site = Site.objects.get_current(request)

        try:
            # can see only permissions for users which are under 
            # him in tree
            qs = self.model.objects.subordinate_to_user(\
                 request.user, site)
        except NoPermissionsException:
            return self.model.objects.none()
        return qs.filter(can_view=self.show_with_view_permissions)

    def get_formset(self, request, obj=None, **kwargs):
        """
        Some fields may be excluded here. User can change only
        permissions which are available for him. E.g. if user does 
        not have can_publish flag, he can't change assign 
        can_publish permissions.
        """
        exclude = self.exclude or []
        if obj:
            user = request.user
            if not obj.has_add_permission(user):
                exclude.append('can_add')
            if not obj.has_delete_permission(user):
                exclude.append('can_delete')
            if not obj.has_publish_permission(user):
                exclude.append('can_publish')
            if not obj.has_advanced_settings_permission(user):
                exclude.append('can_change_advanced_settings')
            if not obj.has_move_page_permission(user):
                exclude.append('can_move_page')

        kwargs['exclude'] = exclude
        formset_cls = super(PagePermissionInlineAdmin, self).\
                        get_formset(request, obj=obj, **kwargs)
        qs = self.get_queryset(request)
        if obj is not None:
            qs = qs.filter(page=obj)
        formset_cls._queryset = qs
        return formset_cls


class ViewRestrictionInlineAdmin(PagePermissionInlineAdmin):
    extra = 0  # edit page load time boost
    form = ViewRestrictionInlineAdminForm
    verbose_name = _("View restriction")
    verbose_name_plural = _("View restrictions")
    show_with_view_permissions = True


class GlobalPagePermissionAdmin(admin.ModelAdmin):
    list_display = ['user', 'group', 'can_change', 'can_delete', 
                    'can_publish', 'can_change_permissions']
    list_filter = ['user', 'group', 'can_change', 'can_delete', 
                   'can_publish', 'can_change_permissions']

    form = GlobalPagePermissionAdminForm
    search_fields = []
    for field in admin_class.search_fields:
        search_fields.append("user__%s" % field)
    search_fields.append('group__name')

    list_display.append('can_change_advanced_settings')
    list_filter.append('can_change_advanced_settings')

~~    def get_list_filter(self, request):
~~        threshold = get_cms_setting('RAW_ID_USERS')
~~        try:
~~            threshold = threshold and \
~~              get_user_model().objects.count() > threshold
~~        except OperationalError:
~~            threshold = False
        filter_copy = deepcopy(self.list_filter)
        if threshold:
            filter_copy.remove('user')
        return filter_copy

    def has_add_permission(self, request):
        site = Site.objects.get_current(request)
        return permissions.\
            user_can_add_global_permissions(request.user, site)

    def has_change_permission(self, request, obj=None):
        site = Site.objects.get_current(request)
        return permissions.\
            user_can_change_global_permissions(request.user, site)

    def has_delete_permission(self, request, obj=None):
        site = Site.objects.get_current(request)
        return permissions.\
            user_can_delete_global_permissions(request.user, site)

    @classproperty
    def raw_id_fields(cls):
        # Dynamically set raw_id_fields based on settings
        threshold = get_cms_setting('RAW_ID_USERS')

        # Given a fresh django-cms install and a django settings
        # with the CMS_RAW_ID_USERS = CMS_PERMISSION = True
        # django throws an OperationalError when running
        # ./manage migrate
        # because auth_user doesn't exists yet
~~        try:
~~            threshold = threshold and get_user_model().\
~~                        objects.count() > threshold
~~        except OperationalError:
~~            threshold = False

        return ['user'] if threshold else []


if get_cms_setting('PERMISSION'):
    admin.site.register(GlobalPagePermission, 
                        GlobalPagePermissionAdmin)
    PERMISSION_ADMIN_INLINES.extend([
        ViewRestrictionInlineAdmin,
        PagePermissionInlineAdmin,
    ])
```


