django ORM 自定义字段

 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 Class(models.Model):
     id = models.AutoField(primary_key=True)
     title = models.CharField(max_length=25)
     # 使用自定义的char类型的字段
     cname = FixedCharField(max_length=25)