urlpattern: first letter to generic class based view

[qvisty]

Hi all. I tried googling. Did not help. I hope you can.
I have a small project with an Article model. It has article.title and article.body.
I have tried making a url pattern for catching “A/” and making it go to a template that only shows all the objects, that begins with the letter a
I can’t figure out how to capture the A in the url and send it to my ListView (which will be filtered).
I tried filtering in both the view and the template.

I can get it working by hardcoding the “A” in my view, but I would like it to read my url and pass the first letter instead. Please help
Some of my code:
views.py

class ArticleListViewByLetter(LoginRequiredMixin, ListView):
    model = Article
    template_name = "article_list_filter.html"

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context["letter"] = "A"
        return context

the urlpatterns line for urls.py:

path(
        "<str:letter>/",
        ArticleListViewByLetter.as_view(),
        name="article_list_filter",
    ),

from my content block in my template file:

This is to test if I have access to the variable: {{ letter }}  (note: I do. It writes A)
{% for article in article_list %}

{% if article.title|first == letter %}

[qvisty]

I sort of got it working doing this in views:

class ArticleListViewByLetter(LoginRequiredMixin, ListView):
    model = Article
    template_name = "article_list_filter.html"

    def get_queryset(self):
        queryset = super(ArticleListViewByLetter, self).get_queryset()
        return Article.objects.filter(title__startswith=self.kwargs["letter"])

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context["letter"] = self.kwargs["letter"]
        return context

But at this point I am just copy pasting around without having a clear idea

[KenWhitesell]

First, you want to do the filtering in get_context_data, not in the template.

The URL parameters are stored within the self.kwargs dict in the view.

You want to override the get_queryset method, to add your filter to the queryset.

Winging this, but it should be something like:

def get_queryset(self):
    queryset = super().get_queryset()
    queryset = queryset.filter(title__startswith=self.kwargs['letter'])
    return queryset

and remove the conditional from the template.

[Edit: I see you almost got it. If you’re going to create the complete queryset within your method, there’s no need to call super - you’re discarding the return from the function, so there’s no need to call it.]

[qvisty]

Thank you Ken. I deleted my own try now and this is my views part now:

class ArticleListViewByLetter(LoginRequiredMixin, ListView):
    model = Article
    template_name = "article_list_filter.html"

    def get_queryset(self):
        queryset = super().get_queryset()
        queryset = queryset.filter(title__startswith=self.kwargs["letter"])
        return queryset

When I open http://127.0.0.1:8000/articles/A/ - nothing shows up. (I have two articles that begins with A)

And the line:
This is to test if I have access to the variable: {{ letter }}
Doesn’t output the variable letter

[KenWhitesell]

Probably the easiest thing to do is to throw a couple of print statements into get_queryset to see what’s happening with the query. (I’d print both self.kwargs[‘letter’] and queryset)

Also, can you post your template?

[qvisty]

my template is here:

{% extends "base.html" %}

{% block title %}Articles{% endblock title %}

{% block content %}
This is to test if I have access to the variable: {{ letter }}
{% for article in article_list %}
{% if article.title|first == letter %}
<p><a href="{% url 'article_detail' article.pk %}">
                {{ article.title }}</a> &middot;
    <em>by {{ article.author }}</em> | {{ article.date }}
<p>{{ article.body }}</p>
<a href="{% url 'article_edit' article.pk %}">Edit</a> |
<a href="{% url 'article_delete' article.pk %}">Delete</a>
<br />
{% endif %}
{% endfor %}
{% endblock content %}

I tried your print statement suggestions:
I opened http://127.0.0.1:8000/articles/A/
and got:

queryset from super().get_queryset():  <QuerySet [<Article: Jesper nye?>, <Article: ny admin artikel>, <Article: And>, <Article: Ananas>]>
queryset from queryset.filter(title__startswith=self.kwargs['letter']):  <QuerySet [<Article: And>, <Article: Ananas>]>
kwargs from self.kwargs['letter']:  A

[KenWhitesell]

Ok, since you’ve already limited your queryset to the articles you’re interested in, now you need to remove the if from your template (along with the corresponding endif).

[qvisty]

Yay! It works! Thank you.

[qvisty]

But now my view only uses the get_queryset, so I still have a bit of confusion about the

def get_queryset(self): 
def get_context_data(self, **kwargs):

Could you please explain the difference?

[KenWhitesell]

Before I can answer this appropriately, how familiar or comfortable are you with the Django generic Class-Based Views?
You’re obviously familiar enough to use them effectively - otherwise you wouldn’t have gotten to this point. So that leaves me a little unsure as to how I need to target my answer.

The quick answer is that the fundamental purpose of get_queryset in a ListView is to create the queryset being used to build the list to be rendered. The get_context_data is available to add other data to the context being rendered by the template.
Yes, you can create the queryset-to-be-rendered-in-the-list in get_context_data, but then your CBV is doing double work. The get_queryset method will still get called, and the base queryset will be created before being overwritten by the queryset created in get_context_data.

I’ll also refer you to two third-party sites that I found have helped my understanding tremendously -

• CCBV
• CBV diagrams

[qvisty]

Thank you so much! Perfect answer.

[qvisty]

I thought about it for a while and now I have one more question.

If I use the get_queryset to filter some data and still want to pass extra data via get_context_data I could do it like:

def get_queryset:
     some stuff to filter...

def get_context_data:
     some stuff to add to context 
     I wont use get_queryset here, as it will get called via get_queryset anyway

Did I get that right?

[KenWhitesell]

Yes, that’s basically it. (Ignoring the illegal syntax because I know you’re just expressing an idea and not demonstrating code.)

[qvisty]

Now I went back and fiddled some more. And something is still a little off. I will post my code below. But just to recap I’m trying to catch a urlpattern like “Articles/A” and it will go to a generic ListView page and show all the articles that starts with A.
I’m hoping to save the A to the context under the key “letter” vis str:letter in the urls.py url pattern and to test if it comes through - can be shown on the page in the template.
I am getting all the right articles from the dtb, but the variable wont show.
Snips from my code:
from the template file:

{% block title %}Articles{% endblock title %}
{% block content %}
This is to test if I have access to the variable: {{ letter }}
{% if letter %}
{{ letter }}
{% endif %}
<br>
This is to demonstrate get_context_data in the view. The time is now: {{ now }}
<br>
{% for article in article_list %}
<!-- Articles show up here - which works on my page-->

my line from urls.py (which I think is where I dont fully understand how to pass the string correctly):

urlpatterns = [
    path("<str:letter>/", ArticleListViewByLetter.as_view(),name="article_list_filter",),
]

views.py:

class ArticleListViewByLetter(LoginRequiredMixin, ListView):
    model = Article
    template_name = "article_list_filter.html"

    def get_queryset(self):
        queryset = super().get_queryset()
        queryset = queryset.filter(title__startswith=self.kwargs["letter"])
        return queryset

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context["now"] = timezone.now()
        return context

I hope you still want to help.
(And I hope people can learn from me exposing my ignorance.)

[KenWhitesell]

You still need to pass the letter through the context to the template to be rendered. You’re adding “now” to the context, you also need to add “letter”.

[qvisty]

I thought I allready did that in this part of the url path in urlpatterns?:

path("<str:letter>/",

[KenWhitesell]

That passes it from the url to the view. Now the view needs to provide it to the rendering engine to make it available to the template - that’s the purpose of the context.

[qvisty]

Yay! Now it works! You are awesome!
I added it, and now it works perfectly. (I hope).
My full view for documenting.

class ArticleListViewByLetter(LoginRequiredMixin, ListView):
    model = Article
    template_name = "article_list_filter.html"

    def get_queryset(self):
        queryset = super().get_queryset()
        queryset = queryset.filter(title__startswith=self.kwargs["letter"])
        return queryset

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context["now"] = timezone.now()
        context["letter"] = self.kwargs["letter"]
        return context

[qvisty]

Since I am still practicing and I get som much good help in here I will share this too.
I was thinking about class based vs. function based and I tried (and somewhat succeeded) in writing both.
Comments are welcome. (I refer back to my own posts and your answers here as my personale stack-overflow
Function-based:

def LetterPagesViewFunctionBased(request, letter):
    pages = Page.objects.filter(title__startswith=letter)
    context = {"letter": letter, 
               "page_list": pages}
    return render(request, "pages/pages_index.html", context)

Class-based:

class LetterPagesView(ListView):
    model = Page
    template_name = "pages/pages_index.html"
    def get_queryset(self):
        queryset = super().get_queryset()
        queryset = queryset.filter(title__startswith=self.kwargs["letter"])
        return queryset
    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context["letter"] = self.kwargs["letter"]
        return context

And for my testing purposes I had them both active with this little change in my
urls.py:

urlpatterns = [
 ...snip...
    path("pages/<str:letter>", LetterPagesView.as_view(), name="LetterPagesView"),
    path("pages/func/<str:letter>", LetterPagesViewFunctionBased, name="LetterPagesViewFunctionBased",
    ),
]

[axeljacobs]

Hi qvisty,

I’m also learing Django, in my little experience at this stage I’m almost always use function based view as there is less ‘magic’ in it. I do write more code but what’s happening in the view is more ‘explicit’.

I guess that with experience I will switch to Class based view as they are certainly more rapid to write.