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Made model fields comparable to other objects

Fixed #17851 -- Added __lt__ and @total_ordering to models.Field,
made sure these work correctly on other objects than Field, too.
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commit 5cbfb48b92cb26a335f9c8c0f79d3390290103e2 1 parent 1aae1cb
@charettes charettes authored akaariai committed
View
15 django/db/models/fields/__init__.py
@@ -12,7 +12,7 @@
from django.core import exceptions, validators
from django.utils.datastructures import DictWrapper
from django.utils.dateparse import parse_date, parse_datetime, parse_time
-from django.utils.functional import curry
+from django.utils.functional import curry, total_ordering
from django.utils.text import capfirst
from django.utils import timezone
from django.utils.translation import ugettext_lazy as _
@@ -45,6 +45,7 @@ class FieldDoesNotExist(Exception):
#
# getattr(obj, opts.pk.attname)
+@total_ordering
class Field(object):
"""Base class for all field types"""
@@ -118,9 +119,17 @@ def __init__(self, verbose_name=None, name=None, primary_key=False,
messages.update(error_messages or {})
self.error_messages = messages
- def __cmp__(self, other):
+ def __eq__(self, other):
+ # Needed for @total_ordering
+ if isinstance(other, Field):
+ return self.creation_counter == other.creation_counter
+ return NotImplemented
+
+ def __lt__(self, other):
# This is needed because bisect does not take a comparison function.
- return cmp(self.creation_counter, other.creation_counter)
+ if isinstance(other, Field):
+ return self.creation_counter < other.creation_counter
+ return NotImplemented
def __deepcopy__(self, memodict):
# We don't have to deepcopy very much here, since most things are not
View
32 django/utils/functional.py
@@ -310,3 +310,35 @@ def partition(predicate, values):
for item in values:
results[predicate(item)].append(item)
return results
+
+try:
+ from functools import total_ordering
+except ImportError:
+ # For Python < 2.7
+ # Code borrowed from python 2.7.3 stdlib
+ def total_ordering(cls):
+ """Class decorator that fills in missing ordering methods"""
+ convert = {
+ '__lt__': [('__gt__', lambda self, other: not (self < other or self == other)),
+ ('__le__', lambda self, other: self < other or self == other),
+ ('__ge__', lambda self, other: not self < other)],
+ '__le__': [('__ge__', lambda self, other: not self <= other or self == other),
+ ('__lt__', lambda self, other: self <= other and not self == other),
+ ('__gt__', lambda self, other: not self <= other)],
+ '__gt__': [('__lt__', lambda self, other: not (self > other or self == other)),
+ ('__ge__', lambda self, other: self > other or self == other),
+ ('__le__', lambda self, other: not self > other)],
+ '__ge__': [('__le__', lambda self, other: (not self >= other) or self == other),
+ ('__gt__', lambda self, other: self >= other and not self == other),
+ ('__lt__', lambda self, other: not self >= other)]
+ }
+ roots = set(dir(cls)) & set(convert)
+ if not roots:
+ raise ValueError('must define at least one ordering operation: < > <= >=')
+ root = max(roots) # prefer __lt__ to __le__ to __gt__ to __ge__
+ for opname, opfunc in convert[root]:
+ if opname not in roots:
+ opfunc.__name__ = opname
+ opfunc.__doc__ = getattr(int, opname).__doc__
+ setattr(cls, opname, opfunc)
+ return cls
View
18 tests/modeltests/basic/tests.py
@@ -3,7 +3,7 @@
from datetime import datetime
from django.core.exceptions import ObjectDoesNotExist
-from django.db.models.fields import FieldDoesNotExist
+from django.db.models.fields import Field, FieldDoesNotExist
from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
from django.utils.translation import ugettext_lazy
@@ -520,6 +520,22 @@ def test_hash_function(self):
s = set([a10, a11, a12])
self.assertTrue(Article.objects.get(headline='Article 11') in s)
+ def test_field_ordering(self):
+ """
+ Field instances have a `__lt__` comparison function to define an
+ ordering based on their creation. Prior to #17851 this ordering
+ comparison relied on the now unsupported `__cmp__` and was assuming
+ compared objects were both Field instances raising `AttributeError`
+ when it should have returned `NotImplemented`.
+ """
+ f1 = Field()
+ f2 = Field(auto_created=True)
+ f3 = Field()
+ self.assertTrue(f2 < f1)
+ self.assertTrue(f3 > f1)
+ self.assertFalse(f1 == None)
+ self.assertFalse(f2 in (None, 1, ''))
+
def test_extra_method_select_argument_with_dashes_and_values(self):
# The 'select' argument to extra() supports names with dashes in
# them, as long as you use values().

3 comments on commit 5cbfb48

@charettes
Collaborator

@akaariai I can't figure out why CI is failing... Re-ran full test suite and everything pass on sqlite3.

@charettes
Collaborator

Argh... I've got 2.7.3 on my machine. It looks like python 2.7 shipped with an incorrect implementation.

@charettes
Collaborator

Here's the python bug report.

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