python – 对Django Q对象执行逻辑异或

我想对 django.db.models.Q对象执行逻辑异或( XOR),使用 operator模块将模型字段的选择限制为外键的子集.我在Django 1.4.3和Python 2.7.2中这样做.我有这样的事情：

import operator

from django.conf import settings
from django.db import models
from django.db.models import Q
from django.contrib.auth.models import User,Group

def query_group_lkup(group_name):
    return Q(user__user__groups__name__exact=group_name)

class Book(models.Model):
    author = models.ForeignKey(
                 User,verbose_name=_("Author"),null=False,default='',related_name="%(app_label)s_%(class)s_author",# This would have provide an exclusive OR on the selected group name for User
                 limit_choices_to=reduce(
                     operator.xor,map(query_group_lkup,getattr(settings,'AUTHORIZED_AUTHORS',''))
                 )

AUTHORIZED_AUTHORS是现有组名的列表.

但这不起作用,因为Q对象不支持^运算符(仅来自docs的|和&运算符).来自stacktrace的消息(部分)如下：

File "/home/moi/.virtualenvs/venv/lib/python2.7/site-packages/django/db/models/loading.py",line 64,in _populate
    self.load_app(app_name,True)
  File "/home/moi/.virtualenvs/venv/lib/python2.7/site-packages/django/db/models/loading.py",line 88,in load_app
    models = import_module('.models',app_name)
  File "/home/moi/.virtualenvs/venv/lib/python2.7/site-packages/django/utils/importlib.py",line 35,in import_module
    __import__(name)
  File "/opt/dvpt/toto/apps/book/models.py",line 42,in <module>
    class Book(models.Model):
  File "/opt/dvpt/toto/apps/book/models.py",line 100,in Book
    map(query_group_lkup,''))
TypeError: unsupported operand type(s) for ^: 'Q' and 'Q'

因此,受到answer的启发,我试图为我的特定查找实现XOR.它不是很灵活,因为查找是硬编码的(我需要在query_xor的参数中使用kwargs,例如……).我最终做了这样的事情：

from django.conf import settings
from django.db import models
from django.db.models import Q
from django.db.models.query import EmptyQuerySet
from django.contrib.auth.models import User,Group

def query_xor_group(names_group):
    """Get a XOR of the queries that match the group names in names_group."""

    if not len(names_group):
        return EmptyQuerySet()
    elif len(names_group) == 1:
        return Q(user__user__groups__name__exact=names_group[0])

    q_chain_or = Q(user__user__groups__name__exact=names_group[0])
    q_chain_and = Q(user__user__groups__name__exact=names_group[0])

    for name in names_group[1:]:
        query = Q(user__user__groups__name__exact=name)
        q_chain_or |= query
        q_chain_and &= query

    return q_chain_or & ~q_chain_and

class Book(models.Model):
    author = models.ForeignKey(
                 User,verbose_name=_("author"),# This provides an exclusive OR on the SELECT group name for User
                 limit_choices_to=query_xor_group(getattr(settings,''))
                 )

它按我的意思工作,但我觉得我不是pythonic(尤其是query_xor_group方法).
这样做会有更好的(更直接的方式)吗？

基本上,我的问题可以被剥夺limit_choices_to部分,并总结为：

如何以Djangonic方式对一组django.db.models.Q对象进行按位异或？

解决方法

from django.db.models import Q

class QQ:
    def __xor__(self,other):    
        not_self = self.clone()
        not_other = other.clone()
        not_self.negate()
        not_other.negate()

        x = self & not_other
        y = not_self & other

        return x | y

Q.__bases__ += (QQ,)

在这之后我能够在filter()调用中进行Q(…)^ Q(…).

Foobar.objects.filter(Q(blah=1) ^ Q(bar=2))

这意味着原始尝试不再抛出不受支持的操作数异常.

limit_choices_to=reduce(
                     operator.xor,''))
                 )

在Python 2.7.5上测试Django 1.6.1

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