如何计算来自 Django 中另一个模型的数据？

Question

I have 2 models and i want to count Foreignkey data, I am trying to count the number of records in related models, but I am unable to count the records, Please let me know how i can Count the data. I want to count this data after filter, I am filtering between 2 dates, it's giving me the current data of using model in filter,but i want to count related model data also using filter.

Here is my models.py file...

class Product(models.Model):
    name=models.CharField(max_length=225)
    customer=models.ForeignKey(Brand, related_name='product_customer',on_delete=models.CASCADE)
    user= models.ForeignKey(Supplement, related_name='product_user', on_delete=models.CASCADE)

created_at = models.DateTimeField(auto_now_add=True)

here is my views.py file...

def index(request):
data = Project.objects.all()
  if request.method == 'POST':
     v1= request.GET.get('created-at')
     if v1:
         v2 = v1.split(' - ')
         s1 = v2[0]
         s2 = v2[1]
         result = Product.objects.filter(created_at__range=[s1,s2])
return render(request, 'index.html' {'result':result})

here is my index.html file..

<p>{{result.count}} product</p>
<p>{{result.product_customer.count}} Customer</p>
<p>{{result.product_user.count}} User</p>

I want to display this data after filter, for product it's working perfect, but i want to display data for customer and user when user filter...

Answer 1

I believe the fastest way to do what you want is to use the annotate function that create new fields ...

result = Product.objects.filter(created_at__range=[s1,s2]).
        annotate(count_customers=Count('customer')).
        annotate(count_users=Count('user'))

... callable in the template:

<p>{{result.count}} product</p>
<p>{{result.count_customers}} Customer</p>
<p>{{result.count_users}} User</p>

Check the official docs for more infos