F object
The previous query used to compare the properties of an object with a constant value. How do the two properties compare? Answer: The use of F objects is defined in django.db.models.
The syntax is as follows:
F(属性名)
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Example: Query books with a reading volume greater than or equal to the review volume.
from django.db.models import F BookInfo.objects.filter(readcount__gt=F('commentcount')) <QuerySet [<BookInfo: 雪山飞狐>]>
You can use arithmetic operations on F objects.
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Example: Query books with a reading volume greater than 2 times the number of reviews.
BookInfo.objects.filter(readcount__gt=F('commentcount')*2) <QuerySet [<BookInfo: 雪山飞狐>]>
Q object
Multiple filters are called one by one to indicate logic and relationship, and the and keyword in the where part of the SQL statement.
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Example: Query books with a reading volume greater than 20 and a number less than 3.
BookInfo.objects.filter(readcount__gt=20,id__lt=3) <QuerySet [<BookInfo: 天龙八部>]>or
BookInfo.objects.filter(readcount__gt=20).filter(id__lt=3) <QuerySet [<BookInfo: 天龙八部>]>
If you need to implement a logical or or query, you need to use the Q () object combined with the | operator, and the Q object is defined in django.db.models.
The syntax is as follows:
Q(属性名__运算符=值)
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Example: Query books with a reading volume greater than 20 and rewrite them as Q objects as follows.
BookInfo.objects.filter(Q(readcount__gt=20))
Q objects can be connected with &, |, & represents logical AND, and | represents logical OR.
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Example: Querying books with a reading volume greater than 20 or a number less than 3 can only be implemented using Q objects
BookInfo.objects.filter(Q(readcount__gt=20)|Q(id__lt=3)) <QuerySet [<BookInfo: 射雕英雄传>, <BookInfo: 天龙八部>, <BookInfo: 雪山飞狐>]>
Before the Q object, you can use the ~ operator to indicate non-not.
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Example: Query books with a number not equal to 3.
BookInfo.objects.filter(~Q(id=3)) <QuerySet [<BookInfo: 射雕英雄传>, <BookInfo: 天龙八部>, <BookInfo: 雪山飞狐>]>
