Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Browse files

Fixed #3283 -- Added support for empty QuerySets via none() method. T…

…hanks for the patch, medhat

git-svn-id: http://code.djangoproject.com/svn/django/trunk@4394 bcc190cf-cafb-0310-a4f2-bffc1f526a37
  • Loading branch information...
commit 13280259a8f3ce8c462dc4b484efc922d60666de 1 parent 31bdd8d
@adrianholovaty adrianholovaty authored
View
8 django/db/models/manager.py
@@ -1,4 +1,4 @@
-from django.db.models.query import QuerySet
+from django.db.models.query import QuerySet, EmptyQuerySet
from django.dispatch import dispatcher
from django.db.models import signals
from django.db.models.fields import FieldDoesNotExist
@@ -41,12 +41,18 @@ def contribute_to_class(self, model, name):
#######################
# PROXIES TO QUERYSET #
#######################
+
+ def get_empty_query_set(self):
+ return EmptyQuerySet(self.model)
def get_query_set(self):
"""Returns a new QuerySet object. Subclasses can override this method
to easily customise the behaviour of the Manager.
"""
return QuerySet(self.model)
+
+ def none(self):
+ return self.get_empty_query_set()
def all(self):
return self.get_query_set()
View
75 django/db/models/query.py
@@ -25,6 +25,9 @@
# Larger values are slightly faster at the expense of more storage space.
GET_ITERATOR_CHUNK_SIZE = 100
+class EmptyResultSet(Exception):
+ pass
+
####################
# HELPER FUNCTIONS #
####################
@@ -168,7 +171,12 @@ def iterator(self):
extra_select = self._select.items()
cursor = connection.cursor()
- select, sql, params = self._get_sql_clause()
+
+ try:
+ select, sql, params = self._get_sql_clause()
+ except EmptyResultSet:
+ raise StopIteration
+
cursor.execute("SELECT " + (self._distinct and "DISTINCT " or "") + ",".join(select) + sql, params)
fill_cache = self._select_related
index_end = len(self.model._meta.fields)
@@ -192,7 +200,12 @@ def count(self):
counter._offset = None
counter._limit = None
counter._select_related = False
- select, sql, params = counter._get_sql_clause()
+
+ try:
+ select, sql, params = counter._get_sql_clause()
+ except EmptyResultSet:
+ return 0
+
cursor = connection.cursor()
if self._distinct:
id_col = "%s.%s" % (backend.quote_name(self.model._meta.db_table),
@@ -523,7 +536,12 @@ def iterator(self):
field_names = [f.attname for f in self.model._meta.fields]
cursor = connection.cursor()
- select, sql, params = self._get_sql_clause()
+
+ try:
+ select, sql, params = self._get_sql_clause()
+ except EmptyResultSet:
+ raise StopIteration
+
select = ['%s.%s' % (backend.quote_name(self.model._meta.db_table), backend.quote_name(c)) for c in columns]
cursor.execute("SELECT " + (self._distinct and "DISTINCT " or "") + ",".join(select) + sql, params)
while 1:
@@ -545,7 +563,12 @@ def iterator(self):
if self._field.null:
self._where.append('%s.%s IS NOT NULL' % \
(backend.quote_name(self.model._meta.db_table), backend.quote_name(self._field.column)))
- select, sql, params = self._get_sql_clause()
+
+ try:
+ select, sql, params = self._get_sql_clause()
+ except EmptyResultSet:
+ raise StopIteration
+
sql = 'SELECT %s %s GROUP BY 1 ORDER BY 1 %s' % \
(backend.get_date_trunc_sql(self._kind, '%s.%s' % (backend.quote_name(self.model._meta.db_table),
backend.quote_name(self._field.column))), sql, self._order)
@@ -562,6 +585,25 @@ def _clone(self, klass=None, **kwargs):
c._kind = self._kind
c._order = self._order
return c
+
+class EmptyQuerySet(QuerySet):
+ def __init__(self, model=None):
+ super(EmptyQuerySet, self).__init__(model)
+ self._result_cache = []
+
+ def iterator(self):
+ raise StopIteration
+
+ def count(self):
+ return 0
+
+ def delete(self):
+ pass
+
+ def _clone(self, klass=None, **kwargs):
+ c = super(EmptyQuerySet, self)._clone(klass, **kwargs)
+ c._result_cache = []
+ return c
class QOperator(object):
"Base class for QAnd and QOr"
@@ -571,10 +613,14 @@ def __init__(self, *args):
def get_sql(self, opts):
joins, where, params = SortedDict(), [], []
for val in self.args:
- joins2, where2, params2 = val.get_sql(opts)
- joins.update(joins2)
- where.extend(where2)
- params.extend(params2)
+ try:
+ joins2, where2, params2 = val.get_sql(opts)
+ joins.update(joins2)
+ where.extend(where2)
+ params.extend(params2)
+ except EmptyResultSet:
+ if not isinstance(self, QOr):
+ raise EmptyResultSet
if where:
return joins, ['(%s)' % self.operator.join(where)], params
return joins, [], params
@@ -628,8 +674,11 @@ def __init__(self, q):
self.q = q
def get_sql(self, opts):
- joins, where, params = self.q.get_sql(opts)
- where2 = ['(NOT (%s))' % " AND ".join(where)]
+ try:
+ joins, where, params = self.q.get_sql(opts)
+ where2 = ['(NOT (%s))' % " AND ".join(where)]
+ except EmptyResultSet:
+ return SortedDict(), [], []
return joins, where2, params
def get_where_clause(lookup_type, table_prefix, field_name, value):
@@ -645,11 +694,7 @@ def get_where_clause(lookup_type, table_prefix, field_name, value):
if in_string:
return '%s%s IN (%s)' % (table_prefix, field_name, in_string)
else:
- # Most backends do not accept an empty string inside the IN
- # expression, i.e. cannot do "WHERE ... IN ()". Since there are
- # also some backends that do not accept "WHERE false", we instead
- # use an expression that always evaluates to False.
- return '0=1'
+ raise EmptyResultSet
elif lookup_type == 'range':
return '%s%s BETWEEN %%s AND %%s' % (table_prefix, field_name)
elif lookup_type in ('year', 'month', 'day'):
View
15 docs/db-api.txt
@@ -525,6 +525,21 @@ Examples::
[datetime.datetime(2005, 3, 20), datetime.datetime(2005, 2, 20)]
>>> Entry.objects.filter(headline__contains='Lennon').dates('pub_date', 'day')
[datetime.datetime(2005, 3, 20)]
+
+``none()``
+~~~~~~~~~~
+
+**New in Django development version**
+
+Returns an ``EmptyQuerySet`` -- a ``QuerySet`` 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.)
+
+Examples::
+
+ >>> Entry.objects.none()
+ []
``select_related()``
~~~~~~~~~~~~~~~~~~~~
View
15 tests/modeltests/lookup/models.py
@@ -191,4 +191,19 @@ def __str__(self):
>>> Article.objects.filter(headline__contains='\\')
[<Article: Article with \ backslash>]
+# none() returns an EmptyQuerySet that behaves like any other QuerySet object
+>>> Article.objects.none()
+[]
+>>> Article.objects.none().filter(headline__startswith='Article')
+[]
+>>> Article.objects.none().count()
+0
+
+# using __in with an empty list should return an empty query set
+>>> Article.objects.filter(id__in=[])
+[]
+
+>>> Article.objects.exclude(id__in=[])
+[<Article: Article with \ backslash>, <Article: Article% with percent sign>, <Article: Article_ with underscore>, <Article: Article 5>, <Article: Article 6>, <Article: Article 4>, <Article: Article 2>, <Article: Article 3>, <Article: Article 7>, <Article: Article 1>]
+
"""}
Please sign in to comment.
Something went wrong with that request. Please try again.