Webdev 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

Should you use React.FC to type your components?

Tue, 07 Dec 2021 00:00:00 +0000

TLDR: No. You should probably not.

const Dialog: React.FC = ({children}) => {
	return (
		...
	)
}

The consensus in the React community now seems to be that, you should avoid using React.FC because it causes the component to implicitly take children. This means the component will accept children, even if they’re not supposed to.

Let’s take a look at the pros and cons of React.FC.

Pros of React.FC

Excplicit return type

In addition to the children prop, React.FC declares an explicit return type for the component. The return type is ReactElement | null; and we will get a type error if we try to return something else from the component.

Why you should use the URL to store state in your application

Sun, 28 Nov 2021 00:00:00 +0000

It seems we have, in the web community, collectively forgotten the role of the URL in storing the state of our application. For good or bad, we’ve started developing websites like they are apps and forgotten one of the key elements of the web. I’ve seen (and built) applications where opening modals, searching, filtering, or navigating a wizard doesn’t change the URL. And this is wrong because it doesn’t fit the web paradigm.

What are HTTP cookies

Thu, 28 Oct 2021 00:00:00 +0000

A HTTP cookie is a small piece of data that a server sends to a user’s web browser. The browser may then store the cookie and send it back to the same server with later requests.

Cookies are used typically to tell if two HTTP requests come from the same browser/user. So for session management, tracking and to a lesser extent personalization

For general data storage on the client, there are more modern APIs.