Django ORM操作练习

from django.db import models
# Create your models here.


class Author(models.Model):
    nid = models.AutoField(primary_key=True)
    name = models.CharField(max_length=32)
    age = models.IntegerField()

    # 与AuthorDetail建立一对一的关系
    authorDetail = models.OneToOneField(to="AuthorDetail", on_delete=models.CASCADE)


class AuthorDetail(models.Model):
    nid = models.AutoField(primary_key=True)
    birthday = models.DateField()
    telephone = models.BigIntegerField()
    addr = models.CharField(max_length=64)


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


class Book(models.Model):
    nid = models.AutoField(primary_key=True)
    title = models.CharField(max_length=32)
    publishDate = models.DateTimeField()
    price = models.DecimalField(max_digits=5, decimal_places=2)

    # 与Publish建立一对多的关系,外键字段建立在多的一方
    publish = models.ForeignKey(to="Publish", to_field="nid", on_delete=models.CASCADE)
    # 与Author表建立多对多的关系,ManyToManyField可以建在两个模型中的任意一个，自动创建第三张表
    authors = models.ManyToManyField(to=‘Author‘, )

    # 查询书籍名称是python的出版社名称，对象点字段的形式查询即可（obj.publish.name）
    ret = models.Book.objects.filter(title=‘python‘).first().publish.name
    print(ret)

# 查询出版社id为1的出版社，出版过哪些书籍。表名加__set
    ret = models.Publish.objects.filter(nid=1).first().book_set.values(‘title‘)
    print(ret)

    # 查询python这本书籍的出版社的邮箱：values(‘关联字段__字段‘)
    ret = models.Book.objects.filter(title=‘python‘).values(‘publish__email‘)
    print(ret)

　　ret = ret = models.Publish.objects.filter(book__title=‘python‘).values(‘email‘)
　　print(ret)

# 查询永丰出版社出版过的书籍名称：values(‘表名__字段‘)
    # 方法一：
    ret = models.Publish.objects.filter(name=‘永丰出版社‘).values(‘book__title‘)
    print(ret)

    # 方法二 
    ret = models.Book.objects.filter(publish__name=‘永丰出版社‘).values(‘title‘)
    print(ret)

from django.db.models import Count, Avg, Sum, Max, Min
    # 查询所有书籍的价格总和
    ret = models.Book.objects.aggregate(Sum(‘price‘))
    print(ret)

    # 查询永丰出版社的所有书籍的平均价格
    ret = models.Publish.objects.values(‘name‘).annotate(avg=Avg(‘book__price‘)).values(‘name‘, ‘avg‘).filter(name=‘永丰出版社‘)
    print(ret)

    # 查询书籍平均价格低于100的出版社：filter(‘字段名__lt‘)
    ret = models.Publish.objects.values(‘name‘).annotate(avg=Avg(‘book__price‘)).values(‘name‘, ‘avg‘).filter(avg__lt=100)
    print(ret)

    # 按照书籍平均价格对出版社进行排序
    ret = models.Publish.objects.values(‘name‘).annotate(avg=Avg(‘book__price‘)).values(‘name‘, ‘avg‘).order_by(‘avg‘)
    print(ret)