Django trying to add up values in the django template - django

Question

Hi Guys I am trying to figure this out but not having any luck.
So I am showing my events in the homepage which shows how many seats are available, once the user has made a booking I would like to minus that from the amount showing on the homepage.
But I am already stuck at adding all the values up for that event in the booking model to minus from that amount.
So this is what I have
model for events
class Events(models.Model):
ACTIVE = (('d', "Deactivated"), ('e', "Expired"), ('a', "Active"), ('b', "Drafts"),)
ALCOHOL = (('0','No bring own alcohol'),('1','There will be complimentary wine pairing'))
user = models.ForeignKey(User, on_delete=models.CASCADE)
title = models.CharField(max_length=50, blank=True, default='')
date = models.DateField()
time = models.TimeField()
price = models.CharField(max_length=240, blank=True, default='')
seats = models.IntegerField()
created_date = models.DateTimeField(auto_now_add=True)
modified_date = models.DateTimeField(auto_now=True)
model for bookings
class Bookings(models.Model):
OPTIONS_STATUS = (('y', "Yes"), ('n', "No"), ('p', "Pending"),)
user = models.ForeignKey(User, on_delete=models.CASCADE)
event = models.ForeignKey(Events, on_delete=models.CASCADE)
eventdate = models.DateField()
event_amount = models.CharField(max_length=50, blank=True, default='')
guests = models.IntegerField()
bookingstatus = models.CharField(max_length=50, default='p', blank=True, choices=OPTIONS_STATUS)
created_date = models.DateTimeField(auto_now_add=True)
modified_date = models.DateTimeField(auto_now=True)
my homepage how I get my data into a loop form the view
today = datetime.now().strftime('%Y-%m-%d')
events_list_data = Events.objects.filter(active='a').filter(Q(date__gte=today)|Q(date=today)).order_by('date')
How I am trying to show this in my template
{% for event_list in events_list_data %}
SHOW WHAT EVER DATA I AM SHOWING NOT NEEDED FOR HELP ON
{% for bookingguests in
event_list.bookings_set.all %}
{{ bookingguests.guests }}
{% endfor %}
Seats Left
{% endif %}

Answer 1

Generally, purpose of templates is not to implement logic. All the logic should go into your views. I would recommend you to do that in your views and either store it in a dict or a list and send it to front-end.
Once the user made a booking, if you want to modify the value on the HTML without reloading, you may need to use jQuery/javascript. Otherwise, if you are fine with reloading the page by rendering it again with calculations from the backend.
By using jQuery:
$("#balance-id").html(logic to get the balance)
By Calculating in views:
from django.db.models import Sum
user_balance = user.balance - events_data.aggregate(Sum('price'))
return render('path/to/template', {'events_list': events_list_object, 'user_balance':user_balance})
In the template:
{{user_balance}} seats left
Let me know in case of any questions.
Note: If you want to write some logic into your templates, use template tags. It can help you with whatever it can with its limited functionality.