Unable to get repr for 無法讀取出mysql中的數據

D:\python_learn\meiduo_project\meiduo_mall\meiduo_mall\apps\goods\views.py:38: UnorderedObjectListWarning: Pagination may yield inconsistent results with an unordered object_list: <class 'goods.models.SKU'> QuerySet.
  paginator = Paginator(skus, 5)
ERROR exception 132 Internal Server Error: /list/115/1/
Traceback (most recent call last):
  File "D:\python_learn\meiduo_project\env\lib\site-packages\django\core\handlers\exception.py", line 41, in inner
    response = get_response(request)
  File "D:\python_learn\meiduo_project\env\lib\site-packages\django\core\handlers\base.py", line 187, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "D:\python_learn\meiduo_project\env\lib\site-packages\django\core\handlers\base.py", line 185, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "D:\python_learn\meiduo_project\env\lib\site-packages\django\views\generic\base.py", line 68, in view
    return self.dispatch(request, *args, **kwargs)
  File "D:\python_learn\meiduo_project\env\lib\site-packages\django\views\generic\base.py", line 88, in dispatch
    return handler(request, *args, **kwargs)
  File "D:\python_learn\meiduo_project\meiduo_mall\meiduo_mall\apps\goods\views.py", line 61, in get
    return render(request, 'list.html', context)
  File "D:\python_learn\meiduo_project\env\lib\site-packages\django\shortcuts.py", line 30, in render
    content = loader.render_to_string(template_name, context, request, using=using)
  File "D:\python_learn\meiduo_project\env\lib\site-packages\django\template\loader.py", line 68, in render_to_string
    return template.render(context, request)
  File "D:\python_learn\meiduo_project\env\lib\site-packages\django\template\backends\jinja2.py", line 81, in render
    return self.template.render(context)
  File "D:\python_learn\meiduo_project\env\lib\site-packages\jinja2\environment.py", line 1090, in render
    self.environment.handle_exception()
  File "D:\python_learn\meiduo_project\env\lib\site-packages\jinja2\environment.py", line 832, in handle_exception
    reraise(*rewrite_traceback_stack(source=source))
  File "D:\python_learn\meiduo_project\env\lib\site-packages\jinja2\_compat.py", line 28, in reraise
    raise value.with_traceback(tb)
  File "D:\python_learn\meiduo_project\meiduo_mall\meiduo_mall\templates\list.html", line 142, in top-level template code
    <a href="detail.html"><img src="{{ sku.default_image_url.url }}"></a>
  File "D:\python_learn\meiduo_project\env\lib\site-packages\jinja2\environment.py", line 471, in getattr
    return getattr(obj, attribute)
jinja2.exceptions.UndefinedError: 'goods.models.SKU object' has no attribute 'default_image_url'

問題：在mysql中查詢數據時，代碼如下：

1 skus = category.sku_set.filter(is_launched=True).order_by(sort_field)

skus 取不到數據，提示 skus: Unable to get repr for <class 'django.db.models.query.QuerySet'>

解決：

多方查找，是因為，原模型類中的

1 default_image_url = models.CharField(max_length=200, default='', null=True, blank=True, verbose_name='默認圖片')

遷移到數據庫中變成了default_image，此時如果把模型類中的default_image_url改成default_image，還會報錯 'str' object has no attribute 'url'

最終改成

1 default_image = models.ImageField(max_length=200, default='', null=True, blank=True, verbose_name='默認圖片')

解決問題！

總結：

1 目前所知只有模型類中的外鍵字段，mysql里會加上 _id，其余字段都是一一對應，不會改變的

2 ImageField 是用於保存圖像文件的字段，有url這個屬性，而CharField 沒有url 這個屬性

3 網上遇到這個問題的人很多，大部分解決辦法有兩個方向

　　1）因為__str__方法返回的有日期，需要轉成str

　　2）遷移模型類出錯，我遇到的錯誤屬於這個范疇