Django复杂模型对象的字符串表示形式（def __str __（self）：）

时间：2018-04-24 17:16:19

标签： python django django-models django-forms django-templates

我一直在使用str处理模型对象的人类可读名称已有一段时间了，但最近我遇到了一些似乎与此函数相关的奇怪崩溃和错误。

我有两个模型SensorAssignment和SnComplex，两者都与第三个模型RadioSn上的列具有OneToOne关系。 RadioSn是所有序列号的主池。 SnComplex是分配给客户的序列号列表，SensorAssignment处理分配给特定物理位置的客户序列号的元数据。

值得注意的是，这是我继承的遗留数据库。有些关系并不理想恕我直言。

以下是仅包含相关列的模型的简化版本。

RadioSn 

class RadioSn(models.Model):
    sn = models.AutoField(primary_key=True)
    role = models.ForeignKey('Roles', db_column='role', on_delete=models.DO_NOTHING)

    class Meta:
        managed = False
        db_table = 'radio_sn'
        ordering = ['sn']

    def __str__(self):
        return '%s -- %s' % (self.sn, self.role)

SnComplex 

class SnComplex(models.Model):
sn = models.OneToOneField(RadioSn, on_delete=models.DO_NOTHING, db_column='sn', primary_key=True)
complex = models.ForeignKey(Complex, on_delete=models.DO_NOTHING, db_column='complex')

class Meta:
    managed = False
    db_table = 'sn_complex'

SensorAssignment 

class SensorAssignment(models.Model):
unit = models.ForeignKey('Unit', on_delete=models.DO_NOTHING, db_column='unit')
sn = models.OneToOneField(RadioSn, on_delete=models.DO_NOTHING, db_column='sn')

class Meta:
    managed = False
    db_table = 'sensor_assignment'
    ordering = ['sn']

def __str__(self):
    return self.pk

这是我们开始遇到问题的地方。我使用form.ModelForm来处理SensorAssignment个对象的创建和维护。因此，对于字段sn，它创建一个html <select>，其中包含RadioSn个对象的选项，这些对象由上面描述的str格式表示（由int主键sn组成的字符串和外键role [错误命名恕我直言]）。

这非常有效（我确实将查询集限制为表单在视图上初始化时的相关选项，因此模型中不是all()个对象。）

Pic of it working

所以我应该可以为SnComplex做同样的事情，对吧？毕竟，每个模型在其各自的RadioSn列上与sn具有相同的关系，并且str对象的RadioSn表示在该模型上完成。

不，这就是我得到的。

Error The line that crashes it

如果我只是将RadioSn个对象表示为self.sn而不是连接self.sn和self.role，那么它适用于两种表单，但是如果我将它连接起来就会崩溃SnComplex 1}}形式。所有RadioSn个对象都有角色值。

任何想法是怎么回事？我们有一个RadioSn模型对象的字符串表示形式，导致SnComplex ModelForm模板渲染崩溃，但在其他地方的多个版本SensorAssignment ModelForm上工作正常。

请求SnComplex表单： 

class AddSensorForm(forms.ModelForm):
    class Meta:
        model = SnComplex
        fields = '__all__'

完整追溯： 

Request Method: GET
Request URL: http://127.0.0.1/complex/33/

Django Version: 2.0.4
Python Version: 3.6.1
Installed Applications:
['apps.dashboard',
 'rest_framework',
 'django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'apps.dashboard.templatetags.custom_filters',
 'widget_tweaks',
 'phonenumber_field',
 'pygal',
 'django_filters']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']


Template error:
In template C:\git\si-dash\apps\dashboard\templates\header.html, error at line 0
   Roles matching query does not exist.
   1 : {% load static %}
   2 : {% load widget_tweaks %}
   3 : {% load custom_filters %}
   4 : {% csrf_token %}
   5 : 
   6 : <!DOCTYPE html>
   7 : <html lang="en">
   8 : 
   9 : <head>
   10 :     <meta charset="utf-8">


Traceback:

File "C:\Python36\lib\site-packages\django\db\models\fields\related_descriptors.py" in __get__
  158.             rel_obj = self.field.get_cached_value(instance)

File "C:\Python36\lib\site-packages\django\db\models\fields\mixins.py" in get_cached_value
  13.             return instance._state.fields_cache[cache_name]

During handling of the above exception ('role'), another exception occurred:

File "C:\Python36\lib\site-packages\django\core\handlers\exception.py" in inner
  35.             response = get_response(request)

File "C:\Python36\lib\site-packages\django\core\handlers\base.py" in _get_response
  128.                 response = self.process_exception_by_middleware(e, request)

File "C:\Python36\lib\site-packages\django\core\handlers\base.py" in _get_response
  126.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "C:\Python36\lib\site-packages\django\contrib\auth\decorators.py" in _wrapped_view
  21.                 return view_func(request, *args, **kwargs)

File "C:\git\si-dash\apps\dashboard\views\complex.py" in complex
  179.     return render(request, 'design/complex.html', passed_data)

File "C:\Python36\lib\site-packages\django\shortcuts.py" in render
  36.     content = loader.render_to_string(template_name, context, request, using=using)

File "C:\Python36\lib\site-packages\django\template\loader.py" in render_to_string
  62.     return template.render(context, request)

File "C:\Python36\lib\site-packages\django\template\backends\django.py" in render
  61.             return self.template.render(context)

File "C:\Python36\lib\site-packages\django\template\base.py" in render
  175.                     return self._render(context)

File "C:\Python36\lib\site-packages\django\template\base.py" in _render
  167.         return self.nodelist.render(context)

File "C:\Python36\lib\site-packages\django\template\base.py" in render
  943.                 bit = node.render_annotated(context)

File "C:\Python36\lib\site-packages\django\template\base.py" in render_annotated
  910.             return self.render(context)

File "C:\Python36\lib\site-packages\django\template\loader_tags.py" in render
  155.             return compiled_parent._render(context)

File "C:\Python36\lib\site-packages\django\template\base.py" in _render
  167.         return self.nodelist.render(context)

File "C:\Python36\lib\site-packages\django\template\base.py" in render
  943.                 bit = node.render_annotated(context)

File "C:\Python36\lib\site-packages\django\template\base.py" in render_annotated
  910.             return self.render(context)

File "C:\Python36\lib\site-packages\django\template\loader_tags.py" in render
  67.                 result = block.nodelist.render(context)

File "C:\Python36\lib\site-packages\django\template\base.py" in render
  943.                 bit = node.render_annotated(context)

File "C:\Python36\lib\site-packages\django\template\base.py" in render_annotated
  910.             return self.render(context)

File "C:\Python36\lib\site-packages\django\template\defaulttags.py" in render
  314.                 return nodelist.render(context)

File "C:\Python36\lib\site-packages\django\template\base.py" in render
  943.                 bit = node.render_annotated(context)

File "C:\Python36\lib\site-packages\django\template\base.py" in render_annotated
  910.             return self.render(context)

File "C:\Python36\lib\site-packages\django\template\defaulttags.py" in render
  211.                     nodelist.append(node.render_annotated(context))

File "C:\Python36\lib\site-packages\django\template\base.py" in render_annotated
  910.             return self.render(context)

File "C:\Python36\lib\site-packages\widget_tweaks\templatetags\widget_tweaks.py" in render
  187.         return str(bounded_field)

File "C:\Python36\lib\site-packages\django\utils\html.py" in <lambda>
  380.     klass.__str__ = lambda self: mark_safe(klass_str(self))

File "C:\Python36\lib\site-packages\django\forms\boundfield.py" in __str__
  36.         return self.as_widget()

File "C:\Python36\lib\site-packages\widget_tweaks\templatetags\widget_tweaks.py" in as_widget
  31.         html = old_as_widget(widget, attrs, only_initial)

File "C:\Python36\lib\site-packages\widget_tweaks\templatetags\widget_tweaks.py" in as_widget
  31.         html = old_as_widget(widget, attrs, only_initial)

File "C:\Python36\lib\site-packages\widget_tweaks\templatetags\widget_tweaks.py" in as_widget
  31.         html = old_as_widget(widget, attrs, only_initial)

File "C:\Python36\lib\site-packages\django\forms\boundfield.py" in as_widget
  118.             **kwargs

File "C:\Python36\lib\site-packages\django\forms\widgets.py" in render
  234.         context = self.get_context(name, value, attrs)

File "C:\Python36\lib\site-packages\django\forms\widgets.py" in get_context
  677.         context = super().get_context(name, value, attrs)

File "C:\Python36\lib\site-packages\django\forms\widgets.py" in get_context
  637.         context['widget']['optgroups'] = self.optgroups(name, context['widget']['value'], attrs)

File "C:\Python36\lib\site-packages\django\forms\widgets.py" in optgroups
  585.         for index, (option_value, option_label) in enumerate(self.choices):

File "C:\Python36\lib\site-packages\django\forms\models.py" in __iter__
  1141.             yield self.choice(obj)

File "C:\Python36\lib\site-packages\django\forms\models.py" in choice
  1147.         return (self.field.prepare_value(obj), self.field.label_from_instance(obj))

File "C:\Python36\lib\site-packages\django\forms\models.py" in label_from_instance
  1213.         return str(obj)

File "C:\git\si-dash\apps\dashboard\models.py" in __str__
  728.         return '%s -- %s' % (self.sn, self.role)

File "C:\Python36\lib\site-packages\django\db\models\fields\related_descriptors.py" in __get__
  164.                 rel_obj = self.get_object(instance)

File "C:\Python36\lib\site-packages\django\db\models\fields\related_descriptors.py" in get_object
  139.         return qs.get(self.field.get_reverse_related_filter(instance))

File "C:\Python36\lib\site-packages\django\db\models\query.py" in get
  403.                 self.model._meta.object_name

Exception Type: DoesNotExist at /complex/33/
Exception Value: Roles matching query does not exist.

1 个答案:

答案 0 :(得分：0)

我正在审核您遇到的问题，我认为这可能是内部加入错误。我查看了DB（非django托管），并且看起来radio_sn.role未设置为外键。

鉴于特定传感器可能存在“坏”角色。它看起来有一个序列号的遗留记录，其角色表中不存在该角色，这是连接错误的根本原因和您获得的“无角色”错误。

我更正了这些记录，并将研究使radio_sn.role成为角色表的外键的步骤。

相关问题
最新问题