Django: Strange error with connection between view, template and url

Question

I have two main usage and main model pages, in which products from a specific usage or model are listed. I have the following views for these pages:

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)

Here we have a get_common_queryset() function, which you can read about the reason of it in this question. Then we have two simillar view functions, products_usage_main and product_model_main but with different templates.

In the urls.py I have following paths for these views:

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

In which, again, we can see that the two paths are similar with just different views.

And finally I have two separate templates for these two views, which their code is not needed or related to the problem I'm facing.

THE PROBLEM:

In my products page sidebar, I have two main links referencing /products/application/ and /products/model/, and when I click on the /products/application/, everything works just fine; but when /products/model/ is clicked, I get the following error:

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

And when I looked into the traceback error, It said that the problem raised from product_detail view and in line product = Product.objects.get(id=pk), which has NOTHING to do with these two pages and their views! Below is my product_detail view:

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)

Below I'm sending complete error traceback in case you need it:

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

Vahid · Accepted Answer · 2022-12-12 15:12:30Z

Inorder to solve this problem, I reviewed my other views, specially the product_detail view, and I tried to understand why this view should be the source of this problem.

In my products/urls.py I had a path to product_detail view, which was as below:

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

On the other hand model page url, as mentioned above, was as below:

    path("model/", products_model_main, name="products_model_main"),

So I guess that the simillarities between these two paths was the source of the problem, and when I changed path url of product_detal to path("product-detail/<str:pk>/, both pages worked just fine.

UPDATE: I found another solution and the main reason for this problem. After changing the product_detail path as mentioned above, it got me thinking about the reason for this problem, because, other than products/model/ I had another url with this structure, products/application/; so, why this problem only occured on model page? Then I checked my urls.py file throughly, and this was full paths in products.urls:

    path("application/", products_usage_main, name="products_usage_main"),
    path("<str:pk>/", product_detail, name="product_detail"),
    path(
        "application/single-application/<str:pk>",
        products_single_usage_list,
        name="products_single_usage_list",
    ),
    path("model/", products_model_main, name="products_model_main"),
    path(
        "application/single-application/sub-application/<str:pk>",
        products_sub_usage_list,
        name="products_sub_usage_list",
    ),
    path(
        "model/single-model/<str:pk>",
        products_single_model_list,
        name="products_single_model_list",
    ),
    path(
        "model/single-model/pump-type/<str:pk>",
        products_single_type_list,
        name="products_single_type_list",
    ),
]

As you can see the order of the urls, first url is products/application/ and the second one is products/<str:pk>; I think Django checks the urls in this order, and it expects the model in products/model/ to be the <str:pk> part in the second url. So, I changed the order of urls, and it just worked fine without any need to change the product_detail page url.

Final urls.py code:

urlpatterns = [
    path("application/", products_usage_main, name="products_usage_main"),
    path("model/", products_model_main, name="products_model_main"),
    path("<str:pk>/", product_detail, name="product_detail"),
    path(
        "application/single-application/<str:pk>",
        products_single_usage_list,
        name="products_single_usage_list",
    ),
    path(
        "application/single-application/sub-application/<str:pk>",
        products_sub_usage_list,
        name="products_sub_usage_list",
    ),
    path(
        "model/single-model/<str:pk>",
        products_single_model_list,
        name="products_single_model_list",
    ),
    path(
        "model/single-model/pump-type/<str:pk>",
        products_single_type_list,
        name="products_single_type_list",
    ),
]

I hope this answer would be helpfull for others who might encounter a problem like this.

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