S20_DAY17--课堂笔记

基于对象查询（子查询）

      一对多 
      
                正向查询，按字段
          Book-------------------->Publish
              <---------------------
                反向查询,按表名小写_set:book_set
      
      
          obj=Book.objects.fliter(title="python").first()
          obj.publish
            
        
      多对多
      
                正向查询，按字段
          Book-------------------->Author
              <---------------------
              查询,按表名小写_set:book_set
      
      
     
          obj=Book.objects.fliter(title="python").first()
          obj.author.all()  #  [obj,....]

      
     一对一：
     
                正向查询，按字段
          Book-------------------->Author
              <---------------------
                查询,按表名小写

基于queryset查询

        
              正向查询，按字段
          A-------------------->B
          <---------------------
        查询,按表名小写

聚合和分组

        
  book   
    
    
    id   title    publish                       
     
    1     php       苹果        
        
    2     python    苹果      
    3     go        橘子

sql：  select publish,Count(*) from Book group by publish   
       
    #查询每一个出版社出版的书籍个数

    # ret=Publish.objects.all().annotate(c=Count("book")).values("name","c")
    # print(ret)


    # 查询每一个作者出版的书籍的平均价格
    ret=Author.objects.all().annotate(price_avg=Avg("book__price")).values("name","price_avg")
    print(ret)

    #查询每一本书籍名称以及作者的个数

    ret=Book.objects.all().annotate(c=Count("author")).values("title","c")
    print(ret)

    # 查询价格大于200的每一本书籍名称以及作者的个数
    ret = Book.objects.filter(price__gt=200).annotate(c=Count("author")).values("title", "c")
    print(ret)

F查询与Q查询


    # F
    from django.db.models import F,Q
    ret=Book.objects.filter(comment_num__gt=F("poll_num"))
    print(ret)
    ret=Book.objects.filter(comment_num__gt=F("read_num")*10)
    print(ret)
    Book.objects.all().update(price=F("price")+100)

    # Q
    ret=Book.objects.filter(title__startswith="java",price__gt=200)
    print(ret)
    ret = Book.objects.filter(Q(title__startswith="java")|~Q(price__lt=200))
    print(ret)

class Book(models.Model):

    title = models.CharField(max_length=32)
    publishDate = models.DateField()
    price = models.DecimalField(max_digits=5, decimal_places=2)   #  999.99

    # 创建一对多的关联字段    :    是与某个书籍对象关联的出版社对象(注意，只有一个对象)
    publish=models.ForeignKey("Publish")

    # 创建的多对多的关系
    authors=models.ManyToManyField("Author")

class Publish(models.Model):
    nid = models.AutoField(primary_key=True)
    name=models.CharField( max_length=32)
    email=models.EmailField()

class Author(models.Model):
    name=models.CharField(max_length=32)
    age=models.IntegerField()
    

class AuthorDetail(models.Model):
    addr=models.CharField(max_length=32)
    email=models.EmailField()
    author=models.OneToOneField("Author")