CODEWITHSUNDEEP
pythondjango
Josh
Josh

Reputation: 285

Listing ForeignKey associated instances within template (queryset within a queryset)

I have a site which catalogs local hikes, and users can log that they have been on the hike. I have a search page which contains the hikes, and one of the fields I'm trying to display is a list of all the people who have been on the hike. I've got this figured out within the individual detail page of the hike, but can't figure out how to create a new queryset within the queryset which is printing the hikes, in order to display this info on a search page.

Here's some code:

models.py:

class Hike(models.Model):
    name = models.CharField(max_length=255, unique=True)
    slug = models.SlugField(unique=True)
    ...

class UserLog(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    hike = models.ForeignKey(Hike, on_delete=models.CASCADE)

views.py:

def hike_list(request):
    qs = Hike.objects.all()
    ... some other filters here
?-->users = UserLog.objects.filter(id=qs.id)

template:

{% for qs in qs %}
{{ hike.name }}{{ hike.other_details_and_stuff }}
?----> {% for users in hikes %}{{ user.name }}{% endfor %}
{% endfor %}

Here's the working code within the individual hike's detail page:

views.py:

def hike_detail (request, slug)
    users = UserLog.objects.filter(hike__slug=slug)

How do I call on the slug from each individual item in the queryset, then run a queryset on that?

Upvotes: 1

Views: 26

Answers (1)

user2390182
user2390182

Reputation: 73490

The easiest is to add a ManyToManyField to Hike:

class Hike(models.Model):
    ...
    users = models.ManyToManyField(User, through='app.UserLog')

If you have no extra fields in UserLog, you can even remove the UserLog model and the through parameter alltogether. In the template you can do:

{% for hike in qs %}
  {{ hike.name }}{{ hike.other_details_and_stuff }}
  {% for user in hike.users.all %}{{ user.name }}{% endfor %}
{% endfor %}

In order avoid too many queries, you should prefetch the users in the Hike query in the view:

qs = Hike.objects.all().prefetch_related('users')

Without the ManyToManyField, you could add a property and user the same template, but the prefetch clause could not be used that easily:

class Hike(models.Model):
    ...
    @property
    def users(self):
        return User.objects.filter(userlog__hike=self)

Upvotes: 1

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