Pagination for the objects returned in 'else' clause - django-models

Question

I have following model, where pagination works ok only if I don't filter by tags. As soon as I filter ads by tags, pagination doesn't work.
class AdListView(ListView):
paginate_by = 2
model = Ad
context_object_name = 'ads'
def get_context_data(self, **kwargs):
if self.request.GET.get('tags') is None:
context = super().get_context_data(**kwargs)
context.update(tags=Tag.objects.all())
return context
else:
tag_submitted = Tag.objects.get(name=self.request.GET.get('tags'))
ads_by_tag = tag_submitted.related_ads.all()
context = {
'ads': ads_by_tag
}
context.update(tags=Tag.objects.all())
return context
What needs to be done so that pagination works for both cases, with and without filter?
below are models.py and template
models.py
class Tag(BaseModel):
def __str__(self):
return str(self.name)
class Ad(BaseModel):
name = models.CharField(max_length=100)
description = models.TextField(max_length=500)
category = models.ForeignKey(Category, on_delete=models.CASCADE)
seller = models.ForeignKey(Seller, on_delete=models.CASCADE)
date_created = models.DateField(auto_now_add=True)
date_modified = models.DateField(auto_now=True)
tags = models.ManyToManyField(Tag, related_name='related_ads')
price = models.PositiveIntegerField(default=0)
archived = models.BooleanField(default=False)
def __str__(self):
return str(self.name)
class Meta:
ordering = ['-date_created']
template
{% block content %}
<div class="container">
<div class="row">
<div class="w-75">
<table class="table">
<thead>
<tr>
<th scope="col">#</th>
<th scope="col">Title</th>
</tr>
</thead>
<tbody>
{% for ad in ads %}
<tr>
<td>{{ forloop.counter }}</td>
<td> {{ ad.name }} </td>
</tr>
{% empty %}
<li>No ads yet.</li>
{% endfor %}
</tbody>
</table>
</div>
<div class="w-25">
<table class="table">
<thead>
<tr>
<th scope="col">Tags</th>
</tr>
</thead>
<tbody>
{% for tag in tags %}
<tr>
<td> {{ tag }} </td>
</tr>
{% empty %}
<li>No tags yet.</li>
{% endfor %}
</tbody>
</table>
</div>
</div>
<div class="row">
<div class="pagination">
<span class="step-links">
{% if page_obj.has_previous %}
« first
previous
{% endif %}
<span class="current">
Page {{ page_obj.number }} of {{ page_obj.paginator.num_pages }}.
</span>
{% if page_obj.has_next %}
next
last »
{% endif %}
</span>
</div>
</div>
</div>
{% endblock %}
so this is a project to learn django, so any other comments on how to improve the code also welcome.

Answer 1

You should not filter in the .get_context_data() [Django-doc]. In Django you pass the (possibly) filtered queryset in .get_queryset(…) [Django-doc]. Django will then paginate the queryset, and add it to the context. By overriding the item in the context, you now have removed the paginated queryset, and added a filtered queryset instead.
You thus provide the filtered queryset, and let Django do the proper pagination:
class AdListView(ListView):
paginate_by = 2
model = Ad
context_object_name = 'ads'
def get_search_querystring(self):
copy = self.request.GET.copy()
copy.pop(self.page_kwarg, None)
return copy.urlencode()
def get_queryset(self, *args, **kwargs):
qs = super().get_queryset(*args, **kwargs)
if 'tags' in self.request.GET:
return qs.filter(tags__name=self.request.GET['tags'])
return qs
def get_context_data(*args, **kwargs):
return super().get_context_data(*args, tags=Tag.objects.all(), **kwargs)
Another problem is the link in the template: by using ?page={{ page_obj.next_page_number }}, this will "drop" the query string [wiki] that contains the search query, and only use page as the only variable in the query string.
In the template we thus can use the URL as:
<a href="?page={{ page_obj.next_page_number }}&{{ view.get_search_queryset|safe }}">
the same should happen with the other pagination links.