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Python Django模型对象的复杂字符串表示形式（def _str__（self）：）

python django django-models

Python Django模型对象的复杂字符串表示形式（def _str__（self）：）,python,django,django-models,django-forms,django-templates,Python,Django,Django Models,Django Forms,Django Templates,我已经用它来处理模型对象的可读名称有一段时间了，但最近我遇到了一些奇怪的崩溃和bug，它们似乎与这个函数有关 我有两种型号SensorAssignment和SnComplex，它们都与第三种型号RadioSn上的一列有一对一的关系无线电n是所有序列号的主池SnComplex是分配给客户的序列列表，SensorAssignment处理分配给特定物理位置的客户序列的元数据 需要注意的是，这是我继承的遗留数据库。有些关系并不理想 以下是模型的简化版本，仅包含相关列 收音机n class RadioSn

我已经用它来处理模型对象的可读名称有一段时间了，但最近我遇到了一些奇怪的崩溃和bug，它们似乎与这个函数有关

我有两种型号
SensorAssignment
和
SnComplex
，它们都与第三种型号
RadioSn
上的一列有一对一的关系<代码>无线电n是所有序列号的主池
SnComplex
是分配给客户的序列列表，
SensorAssignment
处理分配给特定物理位置的客户序列的元数据

需要注意的是，这是我继承的遗留数据库。有些关系并不理想

以下是模型的简化版本，仅包含相关列

收音机n

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'
传感器分配

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
这就是我们开始遇到我的问题的地方。我使用
form.ModelForm
来处理
SensorAssignment
对象的创建和维护。因此，对于
sn
字段，它创建了一个html
，其中包含
RadioSn
对象的选择，这些对象由上面描述的str格式表示（一个由int主键
sn
和外键
角色
[bad naming IMHO]组成的字符串）

这非常有效（我确实将查询集限制为视图上窗体初始化的相关选项，因此它不是模型中的
all（）
对象。）

所以我应该能够为
SnComplex
做同样的事情，对吗？毕竟，每个模型在各自的
sn
列上与
RadioSn
具有相同的关系，并且
str
表示
RadioSn
对象是在该模型上完成的

不，这是我得到的

如果我只是将
RadioSn
对象表示为
self.sn
，而不是将
self.sn
和
self.role
连接起来，它可以在两种形式上工作，但如果我将其连接起来，则会使
SnComplex
形式崩溃。所有
RadioSn
对象都有一个角色值

知道发生了什么事吗？我们有一个
RadioSn
模型对象的字符串表示，它在模板渲染上破坏了
SnComplex
ModelForm
，但在其他地方的多个版本
SensorAssignment
ModelForm
上运行良好

请求的复杂表单：

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

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.
完全回溯：

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

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.

请求方法：获取
请求URL:http://127.0.0.1/complex/33/
Django版本：2.0.4
Python版本：3.6.1
已安装的应用程序：
['apps.dashboard'，
“rest_框架”，
“django.contrib.admin”，
“django.contrib.auth”，
“django.contrib.contenttypes”，
“django.contrib.sessions”，
“django.contrib.messages”，
“django.contrib.staticfiles”，
'应用程序.仪表板.模板标签.自定义过滤器'，
“widget_调整”，
'电话号码\字段'，
“pygal”，
“django_过滤器”]
已安装的中间件：
['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.xframeoptions中间件']
模板错误：
在模板C:\git\si dash\apps\dashboard\templates\header.html中，第0行出现错误
角色匹配查询不存在。
1:{%load static%}
2:{%load widget_tweaks%}
3:{%load custom_filters%}
4:{%csrf_令牌%}
5 : 
6 : 
7 : 
8 : 
9 : 
10 :     
回溯：
get中的文件“C:\Python36\lib\site packages\django\db\models\fields\related\u descriptors.py”__
158rel_obj=self.field.get_缓存值（实例）
get\u cached\u值中的文件“C:\Python36\lib\site packages\django\db\models\fields\mixins.py”
13返回实例。\u state.fields\u缓存[cache\u name]
在处理上述异常（“角色”）期间，发生了另一个异常：
文件“C:\Python36\lib\site packages\django\core\handlers\exception.py”位于内部
35响应=获取响应（请求）
get响应中的文件“C:\Python36\lib\site packages\django\core\handlers\base.py”
128response=self.process\u异常\u由\u中间件（e，请求）
get响应中的文件“C:\Python36\lib\site packages\django\core\handlers\base.py”
126响应=包装的回调（请求，*回调参数，**回调参数）
视图中的文件“C:\Python36\lib\site packages\django\contrib\auth\decorators.py”
21返回视图功能（请求，*args，**kwargs）
复杂文件中的文件“C:\git\si dash\apps\dashboard\views\complex.py”
179返回呈现（请求'design/complex.html'，传递的_数据）
render中的文件“C:\Python36\lib\site packages\django\shortcuts.py”
36content=loader.render_to_string（模板名称、上下文、请求、using=using）
文件“C:\Python36\lib\site packages\django\template\loader.py”位于render\u to\u字符串中
62返回template.render（上下文、请求）
render中的文件“C:\Python36\lib\site packages\django\template\backends\django.py”
61返回self.template.render（上下文）
render中的文件“C:\Python36\lib\site packages\django\template\base.py”
175返回self.\u呈现（上下文）
文件“C:\Python36\lib\site packages\django\template\base.py”位于\u render中
167返回self.nodelist.render（上下文）
render中的文件“C:\Python36\lib\site packages\django\template\base.py”
943位=节点。带注释的渲染（上下文）
render_注释中的文件“C:\Python36\lib\site packages\django\template\base.py”
910返回self.render（上下文）
render中的文件“C:\Python36\lib\site packages\django\template\loader\u tags.py”
15