class FixedCharField(models.Field):
  """
  自定义的 char 类型的字段类
  """
  def __init__(self, max_length, *args, **kwargs):
    self.max_length = max_length
    super(FixedCharField, self).__init__(max_length=max_length, *args, **kwargs)
 
  def db_type(self, connection):
    """
    限定生成数据库表的字段类型为 char，长度为 max_length 指定的值
    """
    return 'char(%s)' % self.max_length

from django.db import models 
class FixedCharField(models.Field):
  """
  自定义的 char 类型的字段类
  """
  def __init__(self, max_length, *args, **kwargs):
    self.max_length = max_length
    super(FixedCharField, self).__init__(max_length=max_length, *args, **kwargs)
 
  def db_type(self, connection):
    """
    限定生成数据库表的字段类型为 char，长度为 max_length 指定的值
    """
    return 'char(%s)' % self.max_length 
class Person(models.Model):
  id = models.AutoField(primary_key=True)  # 自增的 id 主键
  name = models.CharField(max_length=32)
  sex = FixedCharField(max_length=32, default="Man") # 使用上面自定义的char类型的字段
  age = models.IntegerField()
  birthday = models.DateField(auto_now_add=True)