聚合函數與F/Q表達式

聚合函數 取名： field + __ + 聚合函數名字 ，如：price__avg；可傳關鍵字參數修更名字：avg=Avg("price")；

aggregate：不會返回一個 QuerySet 對象，而是返回一個字典，key爲聚合函數的名字，value爲聚合函數執行結果；

annotate：返回一個 QuerySet 對象；

相同點：

1. 均可執行聚合函數；可在任何的‘QuerySet’對象上調用，所以只要返回了‘QuerySet’對象，便可進行鏈式調用，如 index5 中獲取年度銷售總額，可先過濾年份再求聚合函數；

不一樣點：

1.  aggregate 返回一個字典，字典中存儲聚合函數執行的結果；而 annotate 返回一個 QuerySet對象 ，並在查找的模型上添加一個聚合函數的屬性；
2.  aggregate 不會作分組，而 annotate 會使用 Group by 字句進行分組，只有調用該字句才能對每一條數據求聚合函數的值；

• 數據庫中的內容：

 

• models.py文件：

   1 from django.db import models
   2 
   3 class Author(models.Model):
   4     '''做者模型'''
   5     name = models.CharField(max_length=100)
   6     age = models.IntegerField()
   7     email = models.EmailField()
   8 
   9     class Meta:
  10         db_table = 'author'
  11 
  12 class Publisher(models.Model):
  13     '''出版社模型'''
  14     name = models.CharField(max_length=300)
  15 
  16     class Meta:
  17         db_table = 'publisher'
  18 
  19 class Book(models.Model):
  20     '''圖書模型'''
  21     name = models.CharField(max_length=300)
  22     pages = models.IntegerField()
  23     price = models.FloatField()
  24     rating = models.FloatField()
  25     author = models.ForeignKey(Author,on_delete=models.CASCADE)
  26     publisher = models.ForeignKey(Publisher,on_delete=models.CASCADE)
  27 
  28     class Meta:
  29         db_table = 'book'
  30 
  31 class Bookorder(models.Model):
  32     '''圖示訂單模型'''
  33     book = models.ForeignKey('Book',on_delete=models.CASCADE)
  34     price = models.FloatField()
  35     create_time = models.DateTimeField(auto_now_add=True,null=True)
  36 
  37     class Meta:
  38         db_table = 'book_order'

   

• views.py文件：

   1 from django.shortcuts import render
   2 from django.http import HttpResponse
   3 from .models import Author,Publisher,Book,Bookorder
   4 from django.db.models import Avg,Count,Max,Min,Sum
   5 from django.db import connection
   6 
   7 def index(request):
   8     # 獲取全部圖書訂價的平均價（使用aggregate）；Avg：平均值；
   9     result = Book.objects.aggregate(Avg('price'))
  10     print(result)
  11     print(connection.queries)
  12     return HttpResponse('index')
  13     # >>>{'price__avg': 97.25}
  14     # >>>{'price__avg': 97.25}
  15     # {'sql': 'SELECT AVG(`book`.`price`) AS `price__avg` FROM `book`'；
  16 
  17 def index2(requset):
  18     # 獲取每一本銷售的平均價格（使用annotate）；
  19     books = Book.objects.annotate(avg=Avg('bookorder__price'))
  20     for book in books:
  21         print("%s:%s" % (book.name,book.avg))
  22     print(connection.queries)
  23     return HttpResponse('index2')
  24     #三國演義:89.33333333333333
  25     # 水滸傳:93.5
  26     # 西遊記:None
  27     # 紅樓夢:None
  28     # `book_order` ON (`book`.`id` = `book_order`.`book_id`) GROUP BY `book`.`id` ORDER BY NULL'；
  29 
  30 def index3(request):
  31     # book 表中總共有多少本書；
  32     # Count：求某個數據的的個數；
  33     result = Book.objects.aggregate(nums=Count('id'))
  34     # author 表中總共有多少個不一樣的郵箱；
  35     # 使用‘distinct=True’剔除重複的值；
  36     results = Author.objects.aggregate(book_num=Count('email',distinct=True))
  37     
  38     # 統計每本書的銷量
  39     books = Book.objects.annotate(book_nums=Count('bookorder'))
  40     for book in books:
  41         print("%s:%s" % (book.name,book.book_nums))
  42     print(books)
  43     print(connection.queries)
  44     return HttpResponse("index3")
  45     # 三國演義:3
  46     # 水滸傳:2
  47     # 西遊記:0
  48     # 紅樓夢:0
  49 
  50 
  51 def index4(request):
  52     result = Author.objects.aggregate(max=Max('age'),min=Min('age'))
  53     # 每本圖書售賣前的最大及最小价格；
  54     books = Book.objects.annotate(max=Max("bookorder__price"),min=Min("bookorder__price"))
  55     for book in books:
  56         print("%s:%s:%s" % (book.name,book.max,book.min))
  57     print(connection.queries)
  58     return HttpResponse("index4")
  59 
  60     # 三國演義:95.0:85.0
  61     # 水滸傳:94.0:93.0
  62     # 西遊記:None:None
  63     # 紅樓夢:None:None
  64 
  65 
  66 def index5(request):
  67     # 求全部圖書的銷售總額；
  68     result = Book.objects.aggregate(total=Sum("price"))
  69     print(result)
  70     print(connection.queries)
  71     # {'total': 389.0}
  72     # {'sql': 'SELECT SUM(`book`.`price`) AS `total` FROM `book`', 'time': '0.001'}；
  73 
  74     # 求每一本圖書的銷售總額；
  75     books = Book.objects.annotate(total=Sum('bookorder__price'))
  76     for book in books:
  77         print("%s:%s" % (book.name,book.total))
  78     print(connection.queries)
  79     # 三國演義: 268.0
  80     # 水滸傳: 187.0
  81     # 西遊記: None
  82     # 紅樓夢: None
  83     
  84 
  85     # 求2018年度的銷售總額；
  86     result = Bookorder.objects.filter(create_time__year=2019).aggregate(total=Sum("price"))
  87     # 求2018年度每一本圖書的銷售總額；
  88     books = Book.objects.filter(bookorder__create_time__year=2019).annotate(total=Sum("bookorder__price"))
  89     for book in books:
  90         print("%s:%s" % (book.name,book.total)  )
  91     print(connection.queries)
  92     # 三國演義: 268.0
  93     # 水滸傳: 187.0
  94     # `book_order`.`create_time` BETWEEN '2019-01-01 00:00:00' AND '2019-12-31 23:59:59.999999' GROUP BY `book`.`id`

   

 

• F表達式：動態獲取某個字段上的值，不會真正到數據庫中查詢數據，只起一個標識的做用；

   1 def index6(requset):
   2     # 給每本書售價增長10元；update;
   3     Book.objects.update(price=F('price')+10)
   4     print(connection.queries[-1])
   5     # 'UPDATE `book` SET `price` = (`book`.`price` + 10)';
   6 
   7     # Author中name與email相同的內容；
   8     authors = Author.objects.filter(name=F('emile'))
   9     for author in authors:
  10         print("%s:%s" % (author.name,author.email))
  11     return HttpResponse('index6')

   

• Q表達式：包裹查詢條件，可在條件間進行多種操做：與 & 、或 | 、非 ~  等查詢操做；

   1 def index7(requset):
   2     # 一、獲取價格大於100，評分大於4.5的圖書；
   3     # books = Book.objects.filter(price__gte=100,rating=4.5)
   4     books = Book.objects.filter(Q(price__gte=100)&Q(rating__gte=4.5))
   5     for book in books:
   6         print("%s:%s:%s" % (book.name,book.price,book.rating))
   7         
   8     ---
   9 
  10     # 二、獲取價格低於100，或者評分低於4.5分的圖書；
  11     books = Book.objects.filter(Q(price__lt=100)|Q(rating__lt=4.5))
  12     for book in books:
  13         print("%s:%s:%s" % (book.name,book.price,book.rating))
  14        
  15     ---
  16  
  17     # 三、獲取價格大於100，而且圖書名字不包含「傳」字的圖書；
  18     books = Book.objects.filter(Q(price__gte=100)&~Q(name__icontains='傳'))
  19     for book in books:
  20         print("%s:%s:%s" % (book.name,book.price,book.rating))
  21     return HttpResponse('index7')