Django: 使用 Q 对象构建复杂的查询语句

django AND 查询¶OR 查询¶NOT 查询¶与关键字参数共用¶OR, AND, NOT 多条件查询¶动态构建查询条件¶参考资料¶

本文将讲述如何在 Django 项目中使用 Q 对象构建复杂的查询条件。 假设有如下的 model:

class Question(models.Model): question_text = models.CharField(max_length=200) pub_date = models.DateTimeField('date published')

然后我们创建了一些数据：

Question.objects.create( question_text='what are you doing', pub_date=datetime.datetime(2015, 11,7) ) Question.objects.create( question_text='what is wrong with you', pub_date=datetime.datetime(2014, 11, 7) ) Question.objects.create( question_text='who are you', pub_date=datetime.datetime(2015, 10, 7) ) Question.objects.create( question_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 查询¶

将多个 Q 对象作为非关键参数或使用 & 联结即可实现 AND 查询:

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

# Q(…), Q(…) >>> Question.objects.filter(Q(question_text__contains=‘you’), Q(question_text__contains=‘what’)) [<Question: what are you doing>, <Question: what is wrong with you>]

# Q(…) & Q(…) >>> Question.objects.filter(Q(question_text__contains=‘you’) & Q(question_text__contains=‘what’)) [<Question: what are you doing>, <Question: what is wrong with you>]

OR 查询¶

使用 | 联结两个 Q 对象即可实现 OR 查询:

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

NOT 查询¶

使用 ~Q(...) 客户实现 NOT 查询:

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

与关键字参数共用¶

记得要把 Q 对象放前面:

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

OR, AND, NOT 多条件查询¶

这几个条件可以自由组合使用:

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

动态构建查询条件¶

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

>>> lst = [Q(question_text__contains='you'), Q(question_text__contains='who')]

# OR >>> Question.objects.filter(reduce(operator.or_, lst)) [<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_, lst)) [<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名称包含某个关键字）:

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