1 切片操作   Book.objects.all()[0:8]
   2 迭代操作   
         for obj in Book.objects.all():
             print(obj.屬性)
			 
   3 惰性查詢
        ret=Book.objects.all()

		# for i in ret:
		#     print(i)
		#
		# Book.objects.create(title="java",publishDate="2012-12-12",price=12,publish_id=1)
		#
		# for i in ret:
		#     print(i)
      
   4 快取機制
   
        # 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=12,publish_id=1)
		#
		# for i in ret:
		#     print(i)
   

modle：
    model_name=Book._meta.model_name
    app_label=Book._meta.app_label
    title=Book._meta.get_field("title")
	
    print(title)
    print(type(title))

    print(title.max_length)

    price=Book._meta.get_field("price")
    print(price)
    print(type(price))

    print(price.max_digits)