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Fixed #19173 -- Made EmptyQuerySet a marker class only 

The guarantee that no queries will be made when accessing results is
done by new EmptyWhere class which is used for query.where and having.

Thanks to Simon Charette for reviewing and valuable suggestions.
This commit is contained in:
Anssi Kääriäinen 2012-10-24 00:04:37 +03:00
parent a843539af2
commit a2396a4c8f
11 changed files with 96 additions and 177 deletions
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4
django/contrib/auth/models.py
View File

@ -473,8 +473,8 @@ class AnonymousUser(object):
is_staff = False
is_active = False
is_superuser = False
_groups = EmptyManager()
_user_permissions = EmptyManager()
_groups = EmptyManager(Group)
_user_permissions = EmptyManager(Permission)
def __init__(self):
pass

8
django/db/models/manager.py
View File

@ -1,6 +1,6 @@
import copy
from django.db import router
from django.db.models.query import QuerySet, EmptyQuerySet, insert_query, RawQuerySet
from django.db.models.query import QuerySet, insert_query, RawQuerySet
from django.db.models import signals
from django.db.models.fields import FieldDoesNotExist
@ -113,7 +113,7 @@ class Manager(object):
#######################
def get_empty_query_set(self):
return EmptyQuerySet(self.model, using=self._db)
return QuerySet(self.model, using=self._db).none()
def get_query_set(self):
"""Returns a new QuerySet object. Subclasses can override this method
@ -258,5 +258,9 @@ class SwappedManagerDescriptor(object):
class EmptyManager(Manager):
def __init__(self, model):
super(EmptyManager, self).__init__()
self.model = model
def get_query_set(self):
return self.get_empty_query_set()

159
django/db/models/query.py
View File

@ -35,7 +35,6 @@ class QuerySet(object):
"""
def __init__(self, model=None, query=None, using=None):
self.model = model
# EmptyQuerySet instantiates QuerySet with model as None
self._db = using
self.query = query or sql.Query(self.model)
self._result_cache = None
@ -217,7 +216,9 @@ class QuerySet(object):
def __and__(self, other):
self._merge_sanity_check(other)
if isinstance(other, EmptyQuerySet):
return other._clone()
return other
if isinstance(self, EmptyQuerySet):
return self
combined = self._clone()
combined._merge_known_related_objects(other)
combined.query.combine(other.query, sql.AND)
@ -225,9 +226,11 @@ class QuerySet(object):
def __or__(self, other):
self._merge_sanity_check(other)
combined = self._clone()
if isinstance(self, EmptyQuerySet):
return other
if isinstance(other, EmptyQuerySet):
return combined
return self
combined = self._clone()
combined._merge_known_related_objects(other)
combined.query.combine(other.query, sql.OR)
return combined
@ -632,7 +635,9 @@ class QuerySet(object):
"""
Returns an empty QuerySet.
"""
return self._clone(klass=EmptyQuerySet)
clone = self._clone()
clone.query.set_empty()
return clone
##################################################################
# PUBLIC METHODS THAT ALTER ATTRIBUTES AND RETURN A NEW QUERYSET #
@ -981,6 +986,18 @@ class QuerySet(object):
# empty" result.
value_annotation = True
class InstanceCheckMeta(type):
def __instancecheck__(self, instance):
return instance.query.is_empty()
class EmptyQuerySet(six.with_metaclass(InstanceCheckMeta), object):
"""
Marker class usable for checking if a queryset is empty by .none():
isinstance(qs.none(), EmptyQuerySet) -> True
"""
def __init__(self, *args, **kwargs):
raise TypeError("EmptyQuerySet can't be instantiated")
class ValuesQuerySet(QuerySet):
def __init__(self, *args, **kwargs):
@ -1180,138 +1197,6 @@ class DateQuerySet(QuerySet):
return c
class EmptyQuerySet(QuerySet):
def __init__(self, model=None, query=None, using=None):
super(EmptyQuerySet, self).__init__(model, query, using)
self._result_cache = []
def __and__(self, other):
return self._clone()
def __or__(self, other):
return other._clone()
def count(self):
return 0
def delete(self):
pass
def _clone(self, klass=None, setup=False, **kwargs):
c = super(EmptyQuerySet, self)._clone(klass, setup=setup, **kwargs)
c._result_cache = []
return c
def iterator(self):
# This slightly odd construction is because we need an empty generator
# (it raises StopIteration immediately).
yield next(iter([]))
def all(self):
"""
Always returns EmptyQuerySet.
"""
return self
def filter(self, *args, **kwargs):
"""
Always returns EmptyQuerySet.
"""
return self
def exclude(self, *args, **kwargs):
"""
Always returns EmptyQuerySet.
"""
return self
def complex_filter(self, filter_obj):
"""
Always returns EmptyQuerySet.
"""
return self
def select_related(self, *fields, **kwargs):
"""
Always returns EmptyQuerySet.
"""
return self
def annotate(self, *args, **kwargs):
"""
Always returns EmptyQuerySet.
"""
return self
def order_by(self, *field_names):
"""
Always returns EmptyQuerySet.
"""
return self
def distinct(self, fields=None):
"""
Always returns EmptyQuerySet.
"""
return self
def extra(self, select=None, where=None, params=None, tables=None,
order_by=None, select_params=None):
"""
Always returns EmptyQuerySet.
"""
assert self.query.can_filter(), \
"Cannot change a query once a slice has been taken"
return self
def reverse(self):
"""
Always returns EmptyQuerySet.
"""
return self
def defer(self, *fields):
"""
Always returns EmptyQuerySet.
"""
return self
def only(self, *fields):
"""
Always returns EmptyQuerySet.
"""
return self
def update(self, **kwargs):
"""
Don't update anything.
"""
return 0
def aggregate(self, *args, **kwargs):
"""
Return a dict mapping the aggregate names to None
"""
for arg in args:
kwargs[arg.default_alias] = arg
return dict([(key, None) for key in kwargs])
def values(self, *fields):
"""
Always returns EmptyQuerySet.
"""
return self
def values_list(self, *fields, **kwargs):
"""
Always returns EmptyQuerySet.
"""
return self
# EmptyQuerySet is always an empty result in where-clauses (and similar
# situations).
value_annotation = False
def get_klass_info(klass, max_depth=0, cur_depth=0, requested=None,
only_load=None, from_parent=None):
"""

9
django/db/models/sql/query.py
View File

@ -25,7 +25,7 @@ from django.db.models.sql.constants import (QUERY_TERMS, ORDER_DIR, SINGLE,
from django.db.models.sql.datastructures import EmptyResultSet, Empty, MultiJoin
from django.db.models.sql.expressions import SQLEvaluator
from django.db.models.sql.where import (WhereNode, Constraint, EverythingNode,
ExtraWhere, AND, OR)
ExtraWhere, AND, OR, EmptyWhere)
from django.core.exceptions import FieldError
__all__ = ['Query', 'RawQuery']
@ -1511,6 +1511,13 @@ class Query(object):
self.add_filter(('%s__isnull' % trimmed_prefix, False), negate=True,
can_reuse=can_reuse)
def set_empty(self):
self.where = EmptyWhere()
self.having = EmptyWhere()
def is_empty(self):
return isinstance(self.where, EmptyWhere) or isinstance(self.having, EmptyWhere)
def set_limits(self, low=None, high=None):
"""
Adjusts the limits on the rows retrieved. We use low/high to set these,

8
django/db/models/sql/where.py
View File

@ -272,6 +272,14 @@ class WhereNode(tree.Node):
if hasattr(child[3], 'relabel_aliases'):
child[3].relabel_aliases(change_map)
class EmptyWhere(WhereNode):
def add(self, data, connector):
return
def as_sql(self, qn=None, connection=None):
raise EmptyResultSet
class EverythingNode(object):
"""
A node that matches everything.

10
docs/ref/models/querysets.txt
View File

@ -593,15 +593,17 @@ none
.. method:: none()
Returns an ``EmptyQuerySet`` — a ``QuerySet`` subclass that always evaluates to
an empty list. This can be used in cases where you know that you should return
an empty result set and your caller is expecting a ``QuerySet`` object (instead
of returning an empty list, for example.)
Calling none() will create a queryset that never returns any objects and no
query will be executed when accessing the results. A qs.none() queryset
is an instance of ``EmptyQuerySet``.
Examples::
>>> Entry.objects.none()
[]
>>> from django.db.models.query import EmptyQuerySet
>>> isinstance(Entry.objects.none(), EmptyQuerySet)
True
all
~~~

5
docs/releases/1.6.txt
View File

@ -31,6 +31,11 @@ Minor features
Backwards incompatible changes in 1.6
=====================================
* The ``django.db.models.query.EmptyQuerySet`` can't be instantiated any more -
it is only usable as a marker class for checking if
:meth:`~django.db.models.query.QuerySet.none` has been called:
``isinstance(qs.none(), EmptyQuerySet)``
.. warning::
In addition to the changes outlined in this section, be sure to review the

7
tests/modeltests/basic/tests.py
View File

@ -4,6 +4,7 @@ from datetime import datetime
from django.core.exceptions import ObjectDoesNotExist, MultipleObjectsReturned
from django.db.models.fields import Field, FieldDoesNotExist
from django.db.models.query import EmptyQuerySet
from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
from django.utils import six
from django.utils.translation import ugettext_lazy
@ -639,3 +640,9 @@ class ModelTest(TestCase):
Article.objects.bulk_create([Article(headline=lazy, pub_date=datetime.now())])
article = Article.objects.get()
self.assertEqual(article.headline, notlazy)
def test_emptyqs(self):
# Can't be instantiated
with self.assertRaises(TypeError):
EmptyQuerySet()
self.assertTrue(isinstance(Article.objects.none(), EmptyQuerySet))

2
tests/modeltests/get_object_or_404/tests.py
View File

@ -53,7 +53,7 @@ class GetObjectOr404Tests(TestCase):
get_object_or_404, Author.objects.all()
)
# Using an EmptyQuerySet raises a Http404 error.
# Using an empty QuerySet raises a Http404 error.
self.assertRaises(Http404,
get_object_or_404, Article.objects.none(), title__contains="Run"
)

2
tests/modeltests/lookup/tests.py
View File

@ -436,7 +436,7 @@ class LookupTests(TestCase):
])
def test_none(self):
# none() returns an EmptyQuerySet that behaves like any other QuerySet object
# none() returns a QuerySet that behaves like any other QuerySet object
self.assertQuerysetEqual(Article.objects.none(), [])
self.assertQuerysetEqual(
Article.objects.none().filter(headline__startswith='Article'), [])

59
tests/regressiontests/queries/tests.py
View File

@ -9,7 +9,7 @@ from django.conf import settings
from django.core.exceptions import FieldError
from django.db import DatabaseError, connection, connections, DEFAULT_DB_ALIAS
from django.db.models import Count, F, Q
from django.db.models.query import ITER_CHUNK_SIZE, EmptyQuerySet
from django.db.models.query import ITER_CHUNK_SIZE
from django.db.models.sql.where import WhereNode, EverythingNode, NothingNode
from django.db.models.sql.datastructures import EmptyResultSet
from django.test import TestCase, skipUnlessDBFeature
@ -663,31 +663,32 @@ class Queries1Tests(BaseQuerysetTest):
Item.objects.filter(created__in=[self.time1, self.time2]),
['<Item: one>', '<Item: two>']
)
def test_ticket7235(self):
# An EmptyQuerySet should not raise exceptions if it is filtered.
q = EmptyQuerySet()
self.assertQuerysetEqual(q.all(), [])
self.assertQuerysetEqual(q.filter(x=10), [])
self.assertQuerysetEqual(q.exclude(y=3), [])
self.assertQuerysetEqual(q.complex_filter({'pk': 1}), [])
self.assertQuerysetEqual(q.select_related('spam', 'eggs'), [])
self.assertQuerysetEqual(q.annotate(Count('eggs')), [])
self.assertQuerysetEqual(q.order_by('-pub_date', 'headline'), [])
self.assertQuerysetEqual(q.distinct(), [])
self.assertQuerysetEqual(
q.extra(select={'is_recent': "pub_date > '2006-01-01'"}),
[]
)
q.query.low_mark = 1
self.assertRaisesMessage(
AssertionError,
'Cannot change a query once a slice has been taken',
q.extra, select={'is_recent': "pub_date > '2006-01-01'"}
)
self.assertQuerysetEqual(q.reverse(), [])
self.assertQuerysetEqual(q.defer('spam', 'eggs'), [])
self.assertQuerysetEqual(q.only('spam', 'eggs'), [])
Eaten.objects.create(meal='m')
q = Eaten.objects.none()
with self.assertNumQueries(0):
self.assertQuerysetEqual(q.all(), [])
self.assertQuerysetEqual(q.filter(meal='m'), [])
self.assertQuerysetEqual(q.exclude(meal='m'), [])
self.assertQuerysetEqual(q.complex_filter({'pk': 1}), [])
self.assertQuerysetEqual(q.select_related('food'), [])
self.assertQuerysetEqual(q.annotate(Count('food')), [])
self.assertQuerysetEqual(q.order_by('meal', 'food'), [])
self.assertQuerysetEqual(q.distinct(), [])
self.assertQuerysetEqual(
q.extra(select={'foo': "1"}),
[]
)
q.query.low_mark = 1
self.assertRaisesMessage(
AssertionError,
'Cannot change a query once a slice has been taken',
q.extra, select={'foo': "1"}
)
self.assertQuerysetEqual(q.reverse(), [])
self.assertQuerysetEqual(q.defer('meal'), [])
self.assertQuerysetEqual(q.only('meal'), [])
def test_ticket7791(self):
# There were "issues" when ordering and distinct-ing on fields related
@ -1935,8 +1936,8 @@ class CloneTests(TestCase):
class EmptyQuerySetTests(TestCase):
def test_emptyqueryset_values(self):
# #14366 -- Calling .values() on an EmptyQuerySet and then cloning that
# should not cause an error"
# #14366 -- Calling .values() on an empty QuerySet and then cloning
# that should not cause an error
self.assertQuerysetEqual(
Number.objects.none().values('num').order_by('num'), []
)
@ -1952,9 +1953,9 @@ class EmptyQuerySetTests(TestCase):
)
def test_ticket_19151(self):
# #19151 -- Calling .values() or .values_list() on an EmptyQuerySet
# should return EmptyQuerySet and not cause an error.
q = EmptyQuerySet()
# #19151 -- Calling .values() or .values_list() on an empty QuerySet
# should return an empty QuerySet and not cause an error.
q = Author.objects.none()
self.assertQuerysetEqual(q.values(), [])
self.assertQuerysetEqual(q.values_list(), [])