Orm-f & Q object

1.F object

Modify the data without extracting the created object
without F object , According to the content of the previous course , We need to implement a like function ：
1. Create an object , And read the base number of likes
2. On the created object +1
3. Save the object back to the database .
It seems ok , But at the same time 100 Individuals create objects and like , The base number is 10,100 The individual saves the theory into the database at the same time after he likes it , that 100 The data saved by individuals are 10+1, Probably 100 After people like it , The result is 11. amount to 100 The data submitted by individuals to the database is 11.
and F Object directly wraps the value of the database , Use F Object is equivalent to submitting data to this field +=1, Using the lock of the database will 100 Connect individuals . No existence 100 The situation that an individual takes out the field value and saves it . amount to 100=F Personal operation +1

from django.db.models import F
def add_like(request,topic_id):
	topic = Topic.objects.get(id=topic_id)
	topic.like = F(' Like ') + 1
	topic.save()

In addition, you can compare database field values

from django.db.models import F
from bookstore.models import Book
books = Book.objects.filter(mark_price__gt=F('price'))
for book in books:
	print(book.title,' pricing :',book.price,' Present price ：',book.mark_price)

2.Q object

or | And & Not ~ Wait for the operation , quote django.db.models in
Such as

from django.db.models import Q
#  Search pricing and cost are less than 20 Yuan's book 
Book.objects.filter(Q(price__lt=20)|Q(mark_price__lt=20))