Multiply Django field values to get a total - django

Question

I have the following models:
class Supplier(models.Model):
name = models.CharField(max_length=200, null=True)
phone = models.CharField(max_length=200, null=True, blank=True)
email = models.CharField(max_length=200, null=True, blank=True)
date_created = models.DateTimeField(auto_now_add=True, null=True)
class Meta:
ordering = ('name',)
def __str__(self):
return self.name
class Order(models.Model):
supplier = models.ForeignKey(Supplier, on_delete=models.CASCADE)
date_created = models.DateTimeField(auto_now_add=True, null=True)
def __str__(self):
return self.supplier.name
#property
def total(self):
orderitems = self.product_set.all()
total = sum([item.get_total for item in products])
return total
class Product(models.Model):
description = models.CharField(max_length=30)
costprice = models.FloatField(null=True, max_length=99, blank=True)
retailprice = models.FloatField(null=True, max_length=99, blank=True)
barcode = models.CharField(
null=True, max_length=99, unique=True, blank=True)
supplier = models.ForeignKey(
Supplier, on_delete=models.CASCADE, default=5)
on_order = models.ForeignKey(
Order, on_delete=models.CASCADE, null=True, blank=True)
on_order_quantity = models.FloatField(null=True, blank=True)
class Meta:
ordering = ('description',)
def __str__(self):
return self.description
i've created an order object for a given supplier with two products, with different quantities and cost prices.
How do I multiply cost x qty and add up those values in order to reach a total order value?
this is my view
def PurchaseOrder(request, pk_order):
orders = Order.objects.get(id=pk_order)
products = Product.objects.filter(
on_order_id=pk_order).prefetch_related('on_order')
total_products = products.count()
supplier = Product.objects.filter(
on_order_id=pk_order).prefetch_related('on_order')
total_value = Product.objects.filter(
on_order_id=pk_order).aggregate(Sum('costprice'))
context = {
'supplier': supplier,
'products': products,
'orders': orders,
'total_products': total_products,
'total_value': total_value, }
return render(request, 'crmapp/purchase_order.html', context)
at the moment it returns this:
This is my html template
It looks like your post is mostly code; please add some more details.'
Well, I need to show my code
{% extends 'crmapp/base.html' %}
{% load static %}
{% block content %}
<div class='main-site>'>
<h4> Supplier: {{orders.supplier}}</h4>
<h5>Order Number: {{orders.id}}</h5>
<h5>Created on: {{orders.date_created | date:"d/m/Y"}}</h5>
<h6>Total Lines In Order: {{total_products}}</h6>
<button style='margin-bottom:10px' class='btn btn-primary' id="open-popup-1">Edit</button>
<button style='margin-bottom:10px' class='btn btn-success' href="" id="open-popup-1">Print/Export</button>
<input type="search" placeholder="Search any field..." class="form-control search-input" data-table="customers-list"/>
<table class="table table js-sort-table mt32 customers-list" id='myTable'>
<thead class="table" >
<tr>
<th class='header' onclick="sortTable(0)" scope="col">ID</th>
<th class='header' onclick="sortTable(1)" scope="col">Description</th>
<th class='header' onclick="sortTable(3)" scope="col">Order Quantity</th>
<th class='header' onclick="sortTable(2)" scope="col">Cost</th>
</tr>
</thead>
<tbody>
<tr>
{% for product in products %}
<td> {{product.id}}</td>
<td><h6><strong>{{product.description}}</strong></h6></td>
<td>{{product.on_order_quantity |floatformat:0}}</td>
<td>£{{product.costprice |floatformat:2}}</td>
</tr>
</tbody>
{% endfor %}
</table>
<div class='ordertotal'>
<h5>Order Value:</h5>
<h6><strong>{{total_value}}</strong></h6>
</div>
</div>
{% endblock %}

Answer 1

Use the property decorator for the costprice field in the Product Model?
class Product(models.Model):
# define other fields here
#property
def costprice(self):
"Returns retailprice * qty for each product."
return self.on_order_quantity * self.retailprice
Update:
There's clearly some misunderstanding. Therefore I'll try to provide more information.
First Question: "How do I multiply cost x qty"
The property decorator allows you to create fields, which behave like calculated read_only fields. (You don't need to initialize them)
#property
def cost_x_qty(self):
"Returns costprice multiplied by qty for each product."
return self.on_order_quantity * self.costprice
Second Question: "How do I add up those values in order to reach a total order value?"
You can use Aggregation to do this.
You can do the following in your view function:
def PurchaseOrder(request, pk_order):
# some code
grand_total = Product.objects.filter(
on_order_id=pk_order).aggregate(Sum('cost_x_qty'))
# add to context
context['grand_total'] = grand_total
return render(request, 'some_template.html', context)
you can use the grand_total in your template file like this:
{{grant_total}}
Hope that helps