Django reverse lookup of foreign keys

Question

I have a venue, this venue has many events happening there. My models look like this:

class Venue(models.Model):
    title = models.CharField(max_length=200)
    date_published = models.DateTimeField('published date',default=datetime.now, blank=True)
    venue_latitude = models.CharField(max_length=200)
    venue_longitude = models.CharField(max_length=200)
    venue_address = models.CharField(max_length=200)
    venue_city = models.CharField(max_length=200)
    venue_state = models.CharField(max_length=200)
    venue_country = models.CharField(max_length=200)
    description = models.TextField()
    def __unicode__(self):
        return u'%s' % (self.title)

class Event(models.Model):
    title = models.CharField(max_length=200)
    date_published = models.DateTimeField('published date',default=datetime.now, blank=True)
    date_start = models.DateTimeField('start date')
    date_end = models.DateTimeField('end date')
    def __unicode__(self):
        return self.title
    description = models.TextField()
    price = models.IntegerField(null=True, blank=True)
    venue = models.ForeignKey(Venue)

I'd like to display all the events that are happening at a certain venue. How can I do that? My current view looks like:

def detail(request, venue_id):
    venue = get_object_or_404(Venue, pk=venue_id)
    return render(request, 'venue-detail.html', {'venue': venue})

Malfunction

What module do these fields relate too description = models.TextField()? – Electrobiology

Actually, these two models are each in their own app, I just posted them together to explain the point :) – Malfunction

Answer 1

You can use events = venue.event_set to go the other way.

Note that venue.event_set is a manager object, like Event.objects, so you can call .all, .filter, .exclude and similar on it to get a queryset.

See the Django documentation

Seljuk

Great! THanks for that. However, If I want to iterate over the events (for i in events) I'm getting "'RelatedManager' object is not iterable" – Malfunction

How did you change it to QueryObject ? – Prophase

@Prophase venue.event_set.all() or venue.event_set.filter(), usually. – Rebhun

If anyone stills sees the error AttributeError: 'Foo' object has no attribute 'bar_set', you might want to check if related_name is set on the ForeignKey/OneToOneField/ManyToManyField of the child model (Bar) referencing the parent model (Foo). – Diandrous

Will this lookup be fast ? should he add foregin key to Venue ? will it make it faster ? – Hughett

Note that if a "related_name" has been set on the foreign key def, you do not need to append "_set". – Thibeault

Be aware that setting related_name="+" on the ForeignKey will cause this to not be possible (source). – Bireme

Answer 2

To those who have "'RelatedManager' object is not iterable"

Add all to retrieve the elements from the manager.

{% for area in world_areas.all %}

https://mcmap.net/q/168128/-39-relatedmanager-39-object-is-not-iterable-django (cannot add this in comment to the first answer)

Lubin

You just saved my day link. – Corcyra

I was about to create mess in my models before I found this :D – Disastrous

Answer 3

Go the other way round. Use Event model.

def detail(request, venue_id):
    venue = Event.objects.filter(venue__id=venue_id)
    return render(request, 'venue-detail.html', {'venue': venue})

PS: I have never used get_object_or_404(). Modify code accordingly.

Quaternity

So what can I use in my template to display the venue title and all the events happening at this venue? – Malfunction

in the template use {{ event.venue.title }} or as per your variables {{ venue.venue.title }} :) {% for i in venue %} {{ i.venue.title }} – Quaternity

I get that, but how do I display all the events happening at this venue? – Malfunction

the filter returns an array containing all the events that happen at the venue.loop over the array in the templates using the for – Quaternity

venue = Event.objects.filter(venue__id=venue_id) I think this expression will return QuerySet of Event object instead of Venue object. – Didactic

@Didactic read the question being asked. – Assembly

Answer 4

You can use venue.event_set.all() to get all the events that are happening at a certain venue as shown below:

def detail(request, venue_id):
    venue = get_object_or_404(Venue, pk=venue_id)
    events = venue.event_set.all() # Here
    return render(request, 'venue-detail.html', {'events': events})

Arvy