使用 Django Q F 对象构建复杂的查询

from django.db import models
 
class Question(models.Model):
    text = models.CharField(max_length=200)
    pub_date = models.DateTimeField('published_date')
 
    def __unicode__(self):
        return self.text

先在 settings.py 中进行设置：

TIME_ZONE = 'Asia/Shanghai'
 
LANGUAGE_CODE = 'zh-hans'

然后创建一些数据：

>>> Question.objects.create(
    text='what are you doing',
    pub_date=datetime.datetime(2015, 11, 7)
)
>>> Question.objects.create(
    text='what is wrong with you',
    pub_date=datetime.datetime(2014, 11, 7)
)
>>> Question.objects.create(
    text='who are you',
    pub_date=datetime.datetime(2015, 10, 7)
)
>>> Question.objects.create(
    text='who am i',
    pub_date=datetime.datetime(2014, 10, 7)
)
>>> Question.objects.all()
[<Question: what are you doing>, <Question: what is wrong with you>, <Question: who are you>, <Question: who am i>]

----------------------------------------------------------- AND -----------------------------------------------------------

将多个 Q 对象作为非关键字参数或使用 & 联结即可实现 AND 查询

>>> from django.db.models import Q
 
# Q(...)
>>> Question.objects.filter(Q(text__contains = 'you'))
[<Question: what are you doing>, <Question: what is wrong with you>, <Question: who are you>]
 
# Q(...), Q(...)
>>> Question.objects.filter(Q(text__contains = 'you'), Q(text__contains = 'what'))
[<Question: what are you doing>, <Question: what is wrong with you>]
 
# Q(...) & Q(...)
>>> Question.objects.filter(Q(text__contains = 'you') & Q(text__contains = 'what'))
[<Question: what are you doing>, <Question: what is wrong with you>]

----------------------------------------------------------- OR -----------------------------------------------------------

使用 | 联结两个 Q 对象即可实现 OR 查询：

# Q(...) | Q(...)
>>> Question.objects.filter(Q(text__contains = 'you') | Q(text__contains = 'who'))
[<Question: what are you doing>, <Question: what is wrong with you>, <Question: who are you>, <Question: who am i>]

----------------------------------------------------------- NOT -----------------------------------------------------------

使用 ~ 即可实现 NOT 查询：

 

# ~Q(...)
>>> Question.objects.filter(~Q(text__contains = 'you'))
[<Question: who am i>]

 

----------------------------------------------------------- 拓展 -----------------------------------------------------------

想按条件过滤掉某些数据，如何表示“不等于”这个概念呢？

 

>>> Question.objects.filter(text != '')

 

上面这种写法是错误的，正确的写法是：

# exclude
>>> Question.objects.exclude(text = '')
[<Question: what are you doing>, <Question: what is wrong with you>, <Question: who are you>, <Question: who am i>]
 
# ~Q(...)
>>> Question.objects.filter(~Q(text = ''))
[<Question: what are you doing>, <Question: what is wrong with you>, <Question: who are you>, <Question: who am i>]

Q 对象与关键字参数共用

Q 对象可以结合关键字参数一起传递给查询函数，不过需要注意的是要将Q 对象放在关键字参数的前面：

# Q(...), key=value
>>> Question.objects.filter(Q(text__contains = 'you'), text__contains = 'who')
[<Question: who are you>]

OR，AND，NOT 多条件自由组合

# (A OR B) AND C AND (NOT D)
>>> Question.objects.filter((Q(text__contains = 'you') | Q(text__contains = 'who')) & Q(text__contains = 'what') & ~Q(text__contains = 'are'))
[<Question: what is wrong with you>]

动态构建查询条件

比如定义了一个包含一些 Q 对象的列表，那么如何使用这个列表构建 AND 或 OR 查询呢？ 可以使用 operator 和 reduce：

>>> import operator
>>> q_list = [Q(text__contains = 'you'), Q(text__contains = 'who')]
 
# OR
>>> Question.objects.filter(reduce(operator.or_, q_list))
[<Question: what are you doing>, <Question: what is wrong with you>, <Question: who are you>, <Question: who am i>]
 
# AND
>>> Question.objects.filter(reduce(operator.and_, q_list))
[<Question: who are you>]

这个列表也可能是根据用户的输入来构建的，比如简单的搜索功能（搜索一个文章的标题或内容或作者包含某个关键字）：

q = request.GET.get('q', '').strip()
q_list = []
if q:
    for key in ['title__contains', 'content__contains', 'author__contains']:
        q_list.append(Q(**{key: q}))
    queryset = Entry.objects.filter(reduce(operator.or_, q_list))

1、all() ： 查询所有结果
2、filter()
3、get(**kwargs)
4、exclude(**kwargs)
5、value(*field)
6、values_list(*field)
7、order_by(*field)
8、reverse():
9、distinct():
10、count()
11、first():
12: last():
13: exists():