super（type，obj）：obj必须是type的实例或子类型

Question

我在一个小型Django应用程序上工作，并收到一条错误消息，告诉我super(type, obj): obj must be an instance or subtype of type。views.py引入函数后，我从文件中获取了它get_object_or_404。下面views.py提供的文件，

from django.shortcuts import render, get_object_or_404    
from django.http import HttpResponse, HttpResponseRedirect     
from django.views import View     
from .models import URL


# function based view 
def redirect_view(request, shortcode=None, *args, **kwargs):
    obj = get_object_or_404(URL, shortcode=shortcode)
    return HttpResponse("Hello World, the shortcode is {shortcode}".format(shortcode = obj.url))


# class based view 
class ShortenerView(View):

    def get(self, request, shortcode=None,  *args, **kwargs):
        obj = get_object_or_404(URL, shortcode=shortcode)
        return HttpResponse("Hello World 1, the shortcode is {shortcode}".format(shortcode = obj.url))

    def post(self, request, *args, **kwargs):
        return HttpResponse()

完整的错误消息在这里，

TypeError at /b/p6jzbp/
super(type, obj): obj must be an instance or subtype of type
Request Method: GET
Request URL:    http://127.0.0.1:8000/b/p6jzbp/
Django Version: 1.11
Exception Type: TypeError
Exception Value:    
super(type, obj): obj must be an instance or subtype of type
Exception Location: /Users/Chaklader/Documents/Projects/UrlShortener/src/shortener/models.py in all, line 18

该line 18中models.py是qs_main = super(URL, self).all(*args, **kwargs)和models.py文件是在这里，

#  will look for the "SHORTCODE_MAX" in the settings and 
#  if not found, will put the value of 15 there 
SHORTCODE_MAX = getattr(settings, "SHORTCODE_MAX", 15)



class UrlManager(models.Manager):

    def all(self, *args, **kwargs):
        qs_main = super(URL, self).all(*args, **kwargs)
        qs      = qs_main.filter(active = True)
        return qs

    def refresh_shortcodes(self, items = None):

        qs = URL.objects.filter(id__gte=1)
        new_codes = 0

        if items is not None and isinstance(items, int):
            qs = qs.order_by('-id')[:items]

        for q in qs:
            q.shortcode = create_shortcode(q)
            print (q.id, " ", q.shortcode)
            q.save()
            new_codes += 1

        return "# new codes created {id}".format(id = new_codes)


class URL(models.Model):

    url         =  models.CharField(max_length = 220, )
    shortcode   =  models.CharField(max_length = SHORTCODE_MAX, blank = True, unique = True)
    updated     =  models.DateTimeField(auto_now = True)
    timestamp   =  models.DateTimeField(auto_now_add = True)
    active      = models.BooleanField(default = True)

    objects = UrlManager()

    def save(self, *args, **kwargs):

        if self.shortcode is  None or self.shortcode == "":
            self.shortcode = create_shortcode(self)

        super(URL, self).save(*args, **kwargs)

    def __str__(self):
        return str(self.url)

    def __unicode__(self):
        return str(self.url)

    # class Meta:
    #   ordering = '-id'

有人可以向我解释错误的原因以及如何解决吗？如果需要，我愿意提供更多信息。

Answer 1

您应该super使用UrlManager类作为第一个参数而不是URL模型来调用。super不能使用不 相关的 类/类型进行调用：

从文档中

super(type[, object-or- type])：返回将方法调用委托给类型的父级或同级类的代理对象。

因此，您 无法 执行以下操作：

>>> class D:
...    pass
... 
>>> class C:
...    def __init__(self):
...        super(D, self).__init__()
... 
>>> C()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in __init__
TypeError: super(type, obj): obj must be an instance or subtype of type

你应该做：

qs_main = super(UrlManager, self).all(*args, **kwargs)

或在Python 3中：

qs_main = super().all(*args, **kwargs)