Django视图模板URL关联异常：访问model页触发UUID验证错误

问题背景 #

我有两个产品展示页面：main usage和main model，对应的视图代码如下：

def get_common_queryset():
    usage_queryset = Usage.objects.all()
    sub_usage_queryset = SubUsage.objects.all()
    main_model_queryset = MainModel.objects.all()
    pump_type_queryset = PumpType.objects.all()
    queryset_dictionary = {
        "usage_queryset": usage_queryset,
        "sub_usage_queryset": sub_usage_queryset,
        "main_model_queryset": main_model_queryset,
        "pump_type_queryset": pump_type_queryset,
    }
    return queryset_dictionary


def products_usage_main(request):
    queryset_dictionary = get_common_queryset()
    context = queryset_dictionary
    return render(request, "products/products_usage_main.html", context)


def products_model_main(request):
    queryset_dictionary = get_common_queryset()
    context = queryset_dictionary
    return render(request, "products/products_model_main.html", context)

get_common_queryset()用于提供公共查询集，两个视图仅渲染的模板不同。

URL配置：

urlpatterns = [
    path("application/", products_usage_main, name="products_usage_main"),
    path("model/", products_model_main, name="products_model_main"),
]

问题现象 #

点击/products/application/链接可正常访问，但点击/products/model/时抛出以下错误：

ValidationError at /products/model/
['“model” is not a valid UUID.']

错误追溯指向product_detail视图中的product = Product.objects.get(id=pk)行，该视图代码：

def product_detail(request, pk):
    product = Product.objects.get(id=pk)
    head_flow_dataset = HeadFlowDataSet.objects.filter(
        product=product
    ).order_by("flow")
    context_of_view = {
        "product": product,
        "head_flow_dataset_x": [],
        "head_flow_dataset_y": [],
    }
    for head_flow in head_flow_dataset:
        context_of_view["head_flow_dataset_x"].append(head_flow.flow)
        context_of_view["head_flow_dataset_y"].append(head_flow.head)
    queryset_dictionary = get_common_queryset()
    context = {
        **context_of_view,
        **queryset_dictionary,
    }
    return render(request, "products/product_detail.html", context)

完整错误回溯：

Internal Server Error: /products/model/
Traceback (most recent call last):
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\fields\__init__.py", line 2649, in to_python
    return uuid.UUID(**{input_form: value})
  File "C:\Users\Vahid Moradi\AppData\Local\Programs\Python\Python310\lib\uuid.py", line 177, in __init__
    raise ValueError('badly formed hexadecimal UUID string')
ValueError: badly formed hexadecimal UUID string

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\core\handlers\exception.py", line 55, in inner
    response = get_response(request)
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\core\handlers\base.py", line 197, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\products\views.py", line 152, in product_detail
    product = Product.objects.get(id=pk)
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\query.py", line 636, in get
    clone = self._chain() if self.query.combinator else self.filter(*args, **kwargs)
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\query.py", line 1420, in filter
    return self._filter_or_exclude(False, args, kwargs)
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\query.py", line 1438, in _filter_or_exclude
    clone._filter_or_exclude_inplace(negate, args, kwargs)
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\query.py", line 1445, in _filter_or_exclude_inplace
    self._query.add_q(Q(*args, **kwargs))
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\sql\query.py", line 1532, in add_q
    clause, _ = self._add_q(q_object, self.used_aliases)
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\sql\query.py", line 1562, in _add_q
    child_clause, needed_inner = self.build_filter(
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\sql\query.py", line 1478, in build_filter
    condition = self.build_lookup(lookups, col, value)
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\sql\query.py", line 1303, in build_lookup
    lookup = lookup_class(lhs, rhs)
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\lookups.py", line 27, in __init__
    self.rhs = self.get_prep_lookup()
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\lookups.py", line 341, in get_prep_lookup
    return super().get_prep_lookup()
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\lookups.py", line 85, in get_prep_lookup
    return self.lhs.output_field.get_prep_value(self.rhs)
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\fields\__init__.py", line 2633, in get_prep_value
    return self.to_python(value)
  File "D:\Projects\Navid Motor\Website\Django\NavidMotor.com\.venv\lib\site-packages\django\db\models\fields\__init__.py", line 2651, in to_python
    raise exceptions.ValidationError(
django.core.exceptions.ValidationError: ['“model” is not a valid UUID.']
[12/Dec/2022 11:22:53] "GET /products/model/ HTTP/1.1" 500 145337

原因分析 #

Django的URL路由是从上到下匹配的，问题出在product_detail的URL配置顺序上。假设你的product_detail路由是类似这样的：

path("<uuid:pk>/", product_detail, name="product_detail"),

如果这条路由放在了path("model/", ...)的前面，那么当访问/products/model/时，Django会把model当作UUID格式的pk参数传递给product_detail视图，但model显然不是合法的UUID，因此抛出验证错误。

而/products/application/能正常访问，是因为没有和它冲突的路由规则在前面匹配到。

解决方案 #

调整URL路由的顺序，把精确匹配的路由放在动态参数路由的前面，确保model/和application/先被匹配：

urlpatterns = [
    # 精确匹配的路由放在前面
    path("application/", products_usage_main, name="products_usage_main"),
    path("model/", products_model_main, name="products_model_main"),
    # 动态参数路由放在后面
    path("<uuid:pk>/", product_detail, name="product_detail"),
]

这样当访问/products/model/时，Django会优先匹配到products_model_main视图，而不是错误地进入product_detail视图。

内容的提问来源于stack exchange，提问作者Vahid