用于页面上的选择框标签，需要先提供一个二维的二元元组，第一个元素表示存在数据库内真实的值，第二个表示页面上显示的具体内容。在浏览器页面上将显示第二个元素的值。需要结合default选项一起使用
    举例：
    方式一

    1. from django.db import models
    3. class Student(models.Model):
    4.     FRESHMAN = 'FR'
    5.     SOPHOMORE = 'SO'
    6.     JUNIOR = 'JR'
    7.     SENIOR = 'SR'
    8.     GRADUATE = 'GR'
    9.     YEAR_IN_SCHOOL_CHOICES = [
    10.         (FRESHMAN, 'Freshman'),
    11.         (SOPHOMORE, 'Sophomore'),
    12.         (JUNIOR, 'Junior'),
    13.         (SENIOR, 'Senior'),
    14.         (GRADUATE, 'Graduate'),
    15.     ]
    16.     year_in_school = models.CharField(max_length=2,choices=YEAR_IN_SCHOOL_CHOICES,
    17.                                       default=FRESHMAN,)
    19.     def is_upperclass(self):
    20.         return self.year_in_school in {self.JUNIOR, self.SENIOR}

    每次choices更改顺序时都会创建一个新迁移。
    方式二

    1. from django.utils.translation import gettext_lazy as _
    3. class Student(models.Model):
    5.     class YearInSchool(models.TextChoices):
    6.         FRESHMAN = 'FR', _('Freshman')
    7.         SOPHOMORE = 'SO', _('Sophomore')
    8.         JUNIOR = 'JR', _('Junior')
    9.         SENIOR = 'SR', _('Senior')
    10.         GRADUATE = 'GR', _('Graduate')
    12.     year_in_school = models.CharField(
    13.         max_length=2,
    14.         choices=YearInSchool.choices,
    15.         default=YearInSchool.FRESHMAN,
    16.     )
    18.     def is_upperclass(self):
    19.         return self.year_in_school in {
    20.             self.YearInSchool.JUNIOR,
    21.             self.YearInSchool.SENIOR,
    22.         }

    以内部类的方式定义choices字段选项值，该内部类需继承model.Choices、model.IntegerChoices或者IntegerChoices