如何捕获此异常？
如何捕获此异常？
提问于 2014-10-09 11:54:45
这段代码在django/db/models/fields.py中，它创建/定义了一个异常？
class ReverseSingleRelatedObjectDescriptor(six.with_metaclass(RenameRelatedObjectDescriptorMethods)):
# This class provides the functionality that makes the related-object
# managers available as attributes on a model class, for fields that have
# a single "remote" value, on the class that defines the related field.
# In the example "choice.poll", the poll attribute is a
# ReverseSingleRelatedObjectDescriptor instance.
def __init__(self, field_with_rel):
self.field = field_with_rel
self.cache_name = self.field.get_cache_name()
@cached_property
def RelatedObjectDoesNotExist(self):
# The exception can't be created at initialization time since the
# related model might not be resolved yet; `rel.to` might still be
# a string model reference.
return type(
str('RelatedObjectDoesNotExist'),
(self.field.rel.to.DoesNotExist, AttributeError),
{}
)这是在django/db/model/field/related.py中，它引发了上面提到的异常：
def __get__(self, instance, instance_type=None):
if instance is None:
return self
try:
rel_obj = getattr(instance, self.cache_name)
except AttributeError:
val = self.field.get_local_related_value(instance)
if None in val:
rel_obj = None
else:
params = dict(
(rh_field.attname, getattr(instance, lh_field.attname))
for lh_field, rh_field in self.field.related_fields)
qs = self.get_queryset(instance=instance)
extra_filter = self.field.get_extra_descriptor_filter(instance)
if isinstance(extra_filter, dict):
params.update(extra_filter)
qs = qs.filter(**params)
else:
qs = qs.filter(extra_filter, **params)
# Assuming the database enforces foreign keys, this won't fail.
rel_obj = qs.get()
if not self.field.rel.multiple:
setattr(rel_obj, self.field.related.get_cache_name(), instance)
setattr(instance, self.cache_name, rel_obj)
if rel_obj is None and not self.field.null:
raise self.RelatedObjectDoesNotExist(
"%s has no %s." % (self.field.model.__name__, self.field.name)
)
else:
return rel_obj问题是这段代码：
try:
val = getattr(obj, attr_name)
except related.ReverseSingleRelatedObjectDescriptor.RelatedObjectDoesNotExist:
val = None # Does not catch the thrown exception
except Exception as foo:
print type(foo) # Catches here, not above不会捕捉到这个异常
>>>print type(foo)
<class 'django.db.models.fields.related.RelatedObjectDoesNotExist'>
>>>isinstance(foo, related.FieldDoesNotExist)
False和
except related.RelatedObjectDoesNotExist:引发一个AttributeError: 'module' object has no attribute 'RelatedObjectDoesNotExist'
>>>isinstance(foo, related.ReverseSingleRelatedObjectDescriptor.RelatedObjectDoesNotExist)
Traceback (most recent call last):
File "<string>", line 1, in <fragment>
TypeError: isinstance() arg 2 must be a class, type, or tuple of classes and types这可能就是为什么。
回答 4
Stack Overflow用户
发布于 2016-11-17 10:43:10
如果您不想导入相关的模型类，您可以：
except MyModel.related_field.RelatedObjectDoesNotExist:或
except my_model_instance._meta.model.related_field.RelatedObjectDoesNotExist:其中related_field是字段名称。
Stack Overflow用户
发布于 2017-03-16 05:58:31
要在一般情况下捕获此异常，可以这样做
from django.core.exceptions import ObjectDoesNotExist
try:
# Your code here
except ObjectDoesNotExist:
# Handle exceptionStack Overflow用户
发布于 2018-06-14 00:20:14
RelatedObjectDoesNotExist异常是在运行时动态创建的。下面是ForwardManyToOneDescriptor和ReverseOneToOneDescriptor描述符的相关代码片段：
@cached_property
def RelatedObjectDoesNotExist(self):
# The exception can't be created at initialization time since the
# related model might not be resolved yet; `self.field.model` might
# still be a string model reference.
return type(
'RelatedObjectDoesNotExist',
(self.field.remote_field.model.DoesNotExist, AttributeError),
{}
)所以异常继承自<model name>.DoesNotExist和AttributeError。实际上，此异常类型的完整MRO为：
[<class 'django.db.models.fields.related_descriptors.RelatedObjectDoesNotExist'>,
<class '<model module path>.DoesNotExist'>,
<class 'django.core.exceptions.ObjectDoesNotExist'>,
<class 'AttributeError'>,
<class 'Exception'>,
<class 'BaseException'>,
<class 'object'>]基本的要点是，您可以捕获<model name>.DoesNotExist、ObjectDoesNotExist (从django.core.exceptions导入)或AttributeError，任何在您的上下文中最有意义的东西。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/26270042
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