I want to know how many orders are placed by each of the customer

Question

I am having the following models.py

from django.db import models

class Customer(models.Model):
    Person_Id=models.IntegerField()
    Person_Name=models.CharField(max_length=100)
    Address=models.CharField(max_length=500)
    Email=models.EmailField(null=False, default="")

    def __str__(self):
        return self.Person_Name

class Items(models.Model):
    Item_Code=models.IntegerField()
    Item_Name=models.CharField(max_length=200)

    def __str__(self):
        return self.Item_Name

class Orders(models.Model):
    Order_Id=models.ForeignKey(Customer, on_delete=models.CASCADE)
    Item_Name=models.ManyToManyField(Items)
    Order_date=models.DateField()
    Comment=models.CharField(max_length=1000, blank=True)

    def __str__(self):
        return str(self.Order_Id)

admin.py is as follow

from django.contrib import admin
from .models import Customer, Orders, Items

class CustomerDetails(admin.ModelAdmin):
    list_display = ('Person_Name', 'Address', 'Email','total','count')
    readonly_fields = ('total',)
    search_fields = ('Person_Name', 'Email')
    list_filter = ('Address',)
    ordering = ('-Person_Name',)

class OrderDetails(admin.ModelAdmin):
    filter_horizontal = ('Item_Name',)

admin.site.register(Customer, CustomerDetails)
admin.site.register(Items)
admin.site.register(Orders, OrderDetails)

Now, I want to know how many orders are placed by each customer. I know that reverse lookup of foreign keys would be used but I am not getting the proper way.

Answer 1

You can do

class Customer(models.Model):
    Person_Id=models.IntegerField()
    Person_Name=models.CharField(max_length=100)
    Address=models.CharField(max_length=500)
    Email=models.EmailField(null=False, default="")

    def __str__(self):
        return self.Person_Name
    @property
    def order_count(self):
        return Orders.objects.filter(Order_Id=self).count() # or self.orders_set.all().count()

and

class CustomerDetails(admin.ModelAdmin):
    list_display = ('Person_Name', 'Address', 'Email', 'order_count')