ORM和原生SQL的优缺点：
优点：
- 实现了代码与数据操作的解耦合
- 不需自己写原生sql, 提高开发效率
- 防止SQL注入, 通过对象操作的方式，默认就是防止sql注入的。
缺点：
- 牺牲性能， 对象到原生SQL势必会有转换消耗，对性能有一定的影响
- 复杂语句力不从心， 一些复杂的sql语句，用orm对象操作的方式很难实现，就还得用原生sql
Models模型：
Django 的models把数据库表结构映射成了一个个的类， 表里的每个字段就是类的属性。我们都知道数据库有很多字段类型，int,float,char等， Django的models类针对不同的字段也设置了不同的类属性。
AutoField #An IntegerField that automatically increments according to available IDs
BigAutoField #A 64-bit integer, guaranteed to fit numbers from 1 to 9223372036854775807.
BigIntegerField #-9223372036854775808 to 9223372036854775807
BinaryField #A field to store raw binary data. It only supports bytes assignment
BooleanField
CharField
DateField #e.g 2019-04-27
DateTimeField #e.g 2019-04-27 17:53:21
DecimalField
DurationField #storing periods of time ,e.g [DD] [HH:[MM:]]ss[.uuuuuu]"
EmailField
FileField #存储文件
FloatField
ImageField #Inherits all attributes and methods from FileField, but also validates that the uploaded object is a valid image.
IntegerField
GenericIPAddressField #IP地址，支持ipv4
NullBooleanField #Like a BooleanField, but allows NULL as one of the options
PositiveIntegerField #Like an IntegerField, but must be either positive or zero (0). Values from 0 to 2147483647
PositiveSmallIntegerField #only allows positive values from 0 to 32767
SlugField # A slug is a short label for something, containing only letters, numbers, underscores or hyphens.
SmallIntegerField
TextField #A large text field.
TimeField #A time, represented in Python by a datetime.time instance.
URLField
UUIDField
除了普通的表字段，针对外键也有映射
ForeignKey # 外键关联
ManyToManyField #多对多
OneToOneField # 1对1