Writing a Django e- commerce framework OSCON 2012

Transcription

1 Writing a Django e- commerce framework OSCON 2012

2 Me David Winterbottom Tangent Labs, London Head of E- commerce team Python hacker commandlinefu.com, django- oscar

3 Synopsis Motivation Oscar - what problem does it solve? Design decisions - customisation techniques E- commerce tips/advice

4 Motivation

5 Tangent Labs 5 years of e- commerce projects PHP => Python / Django Lots of war stories

6 Books

7 Bookshop domain Millions of products ISBNs, BIC/BISAC categories, authors, publishers Automated feed- driven processing Catalogue Stock Rich data

8 Two tier structure Application tier - serves HTTP requests Processing tier: Download and import feeds Data cleaning and processing Periodic jobs for fulfilment

9 Variations New fulfilment partners Stock/availability logic Multiple payment partners Split- payment sources Multibuy offers, vouchers ebooks!

10 PHP framework Home- rolled web framework Customisation via include path overrides Lots of duplication Hard to upgrade

11 Nailvarnish

12 T- shirts

13 Digital music

14 Bar equipment

15 New requirements Product variations - colours, sizes etc New fulfilment processes: webservices / warehouses Per- customer prices

16 B2B Sales reps, customer hierarchies Tax rules Managed budgets Integration with enterprise partners

17 Original assumptions all broken Domains vary wildly Lots of work- arounds

18 Oscar

19 Requirements Lean - as few assumptions as possible Models domain without duplication without too much meta- data

20

21 Domain modelling Implementation deeply connected to core business concepts...where powerful new features unfold as corollaries to older features.

22

23 Lots of others Satchmo Lightning- Fast- Shop Satchless Django- shop Plata, Mamona, Cartridge,...

24 Design decisions

25 Python Decimal support **kwargs Mixins

26

27 Web framework Well- thought out structure Templating, HTTP, security, caching,... Class- based views

28 Models Models drive the design Capture domain logic Foundation for rest of application

29 Eco- system Haystack (search) South (database migrations) Celery (job queue) Internal libraries

30 Customisation

31 settings.py DEBUG = True

32 settings.py AUTH_PROFILE_MODULE = customer.profile

33 Different approach Key idea: Having the same name/identifier as your parent Subclass and override

34 Templates

35

36 Replace TEMPLATE_LOADERS = ( 'django.template.loaders.filesystem.loader', 'django.template.loaders.app_directories.loader', ) TEMPLATE_DIRS = ( ) '/var/www/project/templates/',

37 Override TEMPLATE_LOADERS = ( 'django.template.loaders.filesystem.loader', 'django.template.loaders.app_directories.loader', ) TEMPLATE_DIRS = ( '/var/www/project/templates/' '/path/to/oscar/', ) parent of Oscar s template directory

38 Override # base.html {% extends 'templates/base.html' %} {% block scripts %} <script src="new.js" type="text/javascript"></script> {% endblock %}

39 Extend # base.html {% extends 'templates/base.html' %} {% block scripts %} <script src="new.js" type="text/javascript"></script> {{ block.super }} {% endblock %}

40 Recap Filename is the ID Use include- path trick to subclass parent Use blocks to provide hook points...but, don t go too far

41 Apps

42 Dynamic loading 1 from django.db.loading import get_model Line = get_model('basket', 'Line') INSTALLED_APPS = ( ) 'oscar.apps.basket'

43 Dynamic loading 1 from django.db.loading import get_model Line = get_model('basket', 'Line') INSTALLED_APPS = ( App label 'oscar.apps.basket' )

44 INSTALLED_APPS = ( 'oscar', 'oscar.apps.catalogue', 'oscar.apps.basket', 'oscar.apps.checkout', 'oscar.apps.order',... )

45 INSTALLED_APPS = ( 'oscar', 'oscar.apps.catalogue', 'myproject.basket', 'oscar.apps.checkout', Same app label as parent app 'oscar.apps.order',... )

46 # myproject/basket/models.py from django.db import models from oscar.apps.basket.abstract_models import \ AbstractLine class Line(AbstractLine): cost_centre = models.charfield(max_length=64) from oscar.apps.basket.models import *

47 INSTALLED_APPS = ( 'oscar', templatetags management commands 'oscar.apps.catalogue', 'oscar.apps.basket', 'oscar.apps.checkout', 'oscar.apps.order',... )

48 Recap App label is the ID Models can overridden and extended

49 Dynamic loading 2 from oscar.core.loading import get_class OrderCreator = get_class('order.utils', 'OrderCreator')

50 # order/utils.py from oscar.apps.order.utils import OrderCreator as \ CoreOrderCreator class OrderCreator(CoreOrderCreator): def allocate_stock(self, line): # Override/extend method...

51 Recap (App module, class name) is the ID Any class can be overridden or extended

52 Tips and advice

53 Log everything...except sensitive customer details.

54 Audit models

55 from django.db import models class NielsenDataFile(models.Model): filepath = models.charfield(max_length=128) PENDING, FAILED, PROCESSED = range(3) status = models.integerfield(default=pending) num_valid_records = models.integerfield() num_invalid_records = models.integerfield() date_downloaded = models.datetimefield(null=true) date_processed = models.datetimefield(null=true)

56 Monitor everything High and low thresholds It s always your fault when things go wrong

57 Service layers Avoid views talking to your models directly See Facade design pattern Anti- corruption layers

58 Generic vs bespoke If you re using a framework, you aren t doing good modelling Capture the domain correctly It s ok to throw away the framework

59 Summary Django is great for modelling complex domains Writing customisable django apps isn t easy Oscar s future: NoSQL - no more EAV

60 Image credits Books: Nail varnish: T-shirts: