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)