Back
Feb 18, 2010

Business logic in models

In my recent project there was a lot of data business logic, so I had to organize this code somehow. In this article I'll describe a few hints on how to it.

Mixins

Simple business logic functions should in models or managers. When there's a lot of them, the can be split in mixins.

# logic.py
class EventLogic(object):
    def start(self):
        if self.condition():
            # ...


# models.py
class Event(models.Model, EventLogic):
    name = models.CharField()
    # ...

Custom exceptions

For business logic errors you should declare custom exception classes. It's not fun to understand what this specific IntegrityError means.

Generic views

When all logic is in model and can throw, say, BusinessLogicException, we can write views like this:

from django.contrib import messages


def event_action(requets, event_id, action):
    # event = get_object_or_404(...)
    try:
        getattr(event, action)(request.user)
    except BusinessLogicException, e:
        messages.warning(request, e.message)

    return redirect(request.POST.get('next') or event)

Subscribe for the news and updates

More thoughts
Feb 3, 2025Technology
Figma for Developers: What Dev Mode Offers and How to Use It

This article explores Figma’s Dev Mode, a tool that streamlines design-to-code translation by enabling precise inspection, automated code generation, and seamless integration with design systems.

Apr 11, 2024Technology
Test Analysis at the Feature Level

In the previous article, we learned about test analysis for a product in general, and now we are ready to go further and look at test analysis for specific features.

May 26, 2017Technology
Tutorial: Django User Registration and Authentication

In this beginners friends article I'll explain how to make authentication with Google account on your Django site and how to make authentication for you REST API.

Dec 1, 2016Technology
How to Use Django & PostgreSQL for Full Text Search

For any project there may be a need to use a database full-text search. We expect high speed and relevant results from this search. When we face such problem, we usually think about Solr, ElasticSearch, Sphinx, AWS CloudSearch, etc. But in this article we will talk about PostgreSQL. Starting from version 8.3, a full-text search support in PostgreSQL is available. Let's look at how it is implemented in the DBMS itself.

Nov 21, 2016Technology
Crawling FTP server with Scrapy

Welcome all who are reading this article. I was given a task of creating a parser (spider) with the Scrapy library and parsing FTP server with data. The parser had to find lists of files on the server and handle each file separately depending on the requirement to the parser.

Jun 25, 2011Technology
Ajax blocks in Django

Quite often we have to write paginated or filtered blocks of information on page. I created a decorator that would automate this process.