Django on dev notes

Dynamic aggregation fields in Django

Tue, 05 Sep 2023 09:33:01 +0000

In this article I will walk you through on how to create dynamic aggregation in Django. By dynamic aggregation I refer to the ability to define the resulting aggregation fields programmatically.

Aggregation is a powerful tool when working with data in Django. With it you can have your database summarize or convert data into the format you need.

Here’s an example of a basic Sum aggregation.

from django.db import models
from django.db.models import Sum

class Order(models.Model):
    total_price = models.DecimalField(max_digits=10, decimal_places=2)

# Calculate the total sum of all order prices
total_sum = Order.objects.aggregate(total=Sum('total_price'))['total']

print(f'Total sum of all order prices: {total_sum}')

We have a Order model with total price. If we want the total sum in some collection of orders (all orders in the example), we can use aggregate with Sum .

Use Model Manager to filter queryset by default

Tue, 18 Jan 2022 00:00:00 +0000

How can you filter a queryset by default so that no matter where you use the model, the filter will be applied?

This can be achieved by creating a custom Manager and overriding its get_queryset method.

For example, if we have a soft delete feature in our app implemented by adding a deleted column, we can force only returing non-deleted objects by creating a custom model manager which filters for deleted=false

Advanced Django queries

Tue, 27 Jul 2021 00:00:00 +0000

Django Framework comes with a powerful ORM and query capabilities built-in. If you’re only familiar with the basics of Djangos Query API, this article will introduce some more advanced queries and methods you can use.

In the examples, I’ll be using the following data models.

class Author(models.Model):
    nickname = models.CharField(max_length=20, null=True, blank=True)
    firstname = models.CharField(max_length=20)
    lastname = models.CharField(max_length=40)
    birth_date = models.DateField()


class Book(models.Model):
    author = models.ForeignKey(Author, related_name="books", on_delete=models.CASCADE)
    title = models.CharField(unique=True, max_length=100)
    category = models.CharField(max_length=50)
    published = models.DateField()
    price = models.DecimalField(decimal_places=2, max_digits=6)
    rating = models.IntegerField()

Filtering

Basic filtering in Django can be done using something called field lookups with the filter method. Field lookups consist of the field and a suffix defining the lookup type. If no suffix is defined, the default behavior is equivalent to using the exact suffix.

Customize Django admin with list_display property

Thu, 23 Jul 2020 23:32:01 +0000

One of the great “batteries included” features Django has, is the automatically generated admin panel. It provides a simple UI for creating, editing and deleting data defined with the Django ORM. In this article we are going to enable the admin user interface for a simple model and customize it from a simple list view to a more user friendly table like interface.

Lets say we have a simple model Item which has two fields nameand price.

Using django-registration for simple user registration

Fri, 05 Jul 2019 21:10:01 +0000

Recently I had to setup a web app with simple one step user registration. After some searching I came accross a Django library called django-registration which seemed like the best way to implement user registration. It features single step and two step registration flows, some simple views and simple installation and configuration. In this blog post I’m going to go over the steps needed to implement user registration in a Django app.