Django ORM (四) annotate,F,Q 查詢

annotate

可以通過計算查詢結果中每一個對象所關聯的對象集合，從而得出總計值(也可以是平均值或總和)，即為查詢集的每一項生成聚合。

from django.shortcuts import render, HttpResponse
from app01 import models
from  app01.models import Book,Author,Publisher
from django.db.models import Avg,Min,Sum,Max

def data_oper(req):
    # 查詢每個出版社書的總價
    obj = models.Book.objects.values("publisher__name").annotate(Sum("price"))
    print(obj)
    return HttpResponse("Hello world")

# 查詢 klvchen 出的書總價格
...
def data_oper(req):
    obj = Book.objects.filter(authors__name="klvchen").aggregate(Sum("price"))
    print(obj)
    return HttpResponse("Hello world")

F查詢

F 使用查詢條件的值,專門取對象中某列值的操作

from django.shortcuts import render, HttpResponse
from app01 import models
from  app01.models import Book,Author,Publisher
from django.db.models import Avg,Min,Sum,Max
from django.db.models import F

# 書籍的價格都加20
def data_oper(req):
    models.Book.objects.all().update(price=F("price")+20)
    return HttpResponse("Hello world")

Q 查詢

Q 構建搜索條件

from django.shortcuts import render, HttpResponse
from app01 import models
from  app01.models import Book,Author,Publisher
from django.db.models import Avg,Min,Sum,Max
from django.db.models import F,Q
from django.db.models import F,Q

# 查詢 book 表 id 為3的書名，這里書名是因為在 models.py 定義的 class Book 里面 __str__ 返回的是 title 字段
def data_oper(req):
    obj = models.Book.objects.filter(Q(id=3))[0]
    print(obj)
    return HttpResponse("Hello world")

.....
from django.db.models import F,Q

# 查詢 book 表 id為3或者 title 為 GO 的記錄
def data_oper(req):
    obj = models.Book.objects.filter(Q(id=3)|Q(title="GO"))
    print(obj)
    return HttpResponse("Hello world")

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

from django.db.models import F,Q

def data_oper(req):
    obj = models.Book.objects.filter(Q(price__gt=50)&(Q(id=3)|Q(title="php")), publisher_id=1)
    print(obj)
    return HttpResponse("Hello world")