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.


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

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

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(...)
        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
Mar 18, 2024Technology
From boring to exciting: turn learning to code into an adventure

Tired of boring programming courses where you're forced to read thick textbooks and write code that's never used? Need a platform that makes learning fun and exciting? Then you're in the right place!

May 9, 2018Technology
How to Generate PDF Files in Python with Xhtml2pdf, WeasyPrint or Unoconv

Programmatic generation of PDF files is a frequent task when developing applications that can export reports, bills, or questionnaires. In this article, we will consider three common tools for creating PDFs, including their installation and converting principles.

Sep 22, 2016Technology
Angular Form Validation

In this article, we will describe some useful scripts and directives we use with angular form validation in our projects.

Oct 11, 2010Technology
Char search in Emacs as in Vim

In VIM there is a command for char search: f. After first use it can be repeated with ;. I like to navigate in line with it. You see that you need to go to bracket in a middle of a line - you press f( and one-two ; and you are there. There's no such command in Emacs, so I had to write my own. I've managed even to implement repetition with ;.

Jul 1, 2010Technology
Overriding QuerySet in Django

As you know, model managers can be overriden in Django. It's convenient to add custom filtration method.

Mar 6, 2010Technology
Ajax form validation

There was a task to submit form with ajax, with server side validation of course. Obvious solution is to do validation and return json with erros. I didn't like idea of writing separate view for validation and then inserting errors in form html on client side. Especially since I already had a generic template for django form with errors display. In this article I'll describe how I solved the task.