9 ORM-高阶补充（未完成）

https://www.cnblogs.com/alice-bj/p/9195846.html#_labelTop

https://www.cnblogs.com/yuanchenqi/articles/7570003.html

Queryset:

    切片操作   Book.objects.all()[:]
    迭代操作
         for obj in Book.objects.all():
             print(obj.属性)

    惰性查询
        ret=Book.objects.all()

        # for i in ret:
        #     print(i)
        #
        # Book.objects.create(title="java",publishDate="2012-12-12",price=,publish_id=)
        #
        # for i in ret:
        #     print(i)

    缓存机制

        # ret=Book.objects.all().exists()
        # if ret:
        #     print("OK")

        # ret=Book.objects.all().iterator()
        # print(type(ret))
        # for i in ret:
        #     print(i)
        # Book.objects.create(title="hello2",publishDate="2012-12-12",price=,publish_id=)
        #
        # for i in ret:
        #     print(i)