标签：reduce bsp strip() price contains value nta text not
Django 提供 F() 来做这样的比较。F() 的实例可以在查询中引用字段，来比较同一个 model 实例中两个不同字段的值。
查询书id大于\小于价格的书籍
1 models.Book.objects.filter(id__gt=F("price")) 2 <QuerySet []> 3 4 models.Book.objects.filter(id__lt=F("price")) 5 <QuerySet [<Book: 书一>, <Book: 书二>, <Book: 书三>, <Book: 书四>, <Book: 书五>, <Book: 书六>]>
Django 支持 F() 对象之间以及 F() 对象和常数之间的加减乘除和取模的操作。
1 models.Book.objects.filter(id__lt=F("price")/2) 2 <QuerySet [<Book: 书一>, <Book: 书二>, <Book: 书三>, <Book: 书四>, <Book: 书五>]>
修改操作也可以使用F函数,比如将每一本书的价格提高30元
models.Book.objects.all().update(price=F("price")+30)
字符串使用Concat连接
from django.db.models.functions import Concat from django.db.models import Value models.Book.objects.update(title=Concat(F("title"),Value("("),Value("第"),Value(")")))
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>]
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>]
使用 ~Q(...) 客户实现 NOT 查询:
# ~Q(...) >>> Question.objects.filter(~Q(question_text__contains=‘you‘)) [<Question: who am i>]
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>]
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))
标签：reduce bsp strip() price contains value nta text not
原文地址：https://www.cnblogs.com/Stay-J/p/10349078.html
