Complex lookups with Q objects(Q對象的複雜查詢)
僅僅靠單一的關鍵字參數查詢已經很難滿足查詢要求。此時Django爲我們提供了Q查詢:
class Q
1、Q對象(django.db.models.Q)可以對關鍵字參數進行封裝,從而更好地應用多個查詢,下面是最簡單的例子:
from django.db.models import Q
from login.models import New #假設在我的login app的models.py下有New數據類
q1=New.objects.filter(Q(question__startswith='What'))
2、可以組合使用&,|操作符,當一個操作符是用於兩個Q的對象,它產生一個新的Q對象。
Q(question__startswith='Who') | Q(question__startswith='What')
3、Q對象可以用~操作符放在前面表示否定,也可允許否定與不否定形式的組合
Q(question__startswith='Who') | ~Q(pub_date__year=2005)
4、應用範圍:
Each lookup function that takes keyword-arguments (e.g. filter(), exclude(), get()) can also be passed one or more Q objects as positional (not-named) arguments. If you provide multiple Q object arguments to a lookup function, the arguments will be “AND”ed together. For example:
Poll.objects.get(
Q(question__startswith='Who'),
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6))
)
... roughly translates into the SQL:
SELECT * from polls WHERE question LIKE 'Who%'
AND (pub_date = '2005-05-02' OR pub_date = '2005-05-06')
5、Q對象可以與關鍵字參數查詢一起使用,不過一定要把Q對象放在關鍵字參數查詢的前面。
正確:
Poll.objects.get(
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6)),
question__startswith='Who')
錯誤:
Poll.objects.get(
question__startswith='Who',
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6)))
轉自:http://www.cnblogs.com/BeginMan/archive/2013/04/17/3026243.html