# 创建一个自定义的字段

 class MycharField(models.Field):

     def __inif__(self, max_lenth, *args, **kwargs):

         super(MycharField, self).__init__(max_length=max_lenth, *args, **kwargs)

         self.length = max_lenth

     def db_type(self, connection):

         """

         限定生成数据库变得字段类型为char，长度为max_length指定的值

         :param connection:

         :return:

         """

         return 'char(%s)' % self.max_length