Oscar and the Art of Transactional Django Applications

Oscar is a Django e-commerce framework designed for flexibility. Based on years of hard-earned experience, it employs a range of techniques that allow developers to customise any part of the core. In this way it can be used to build a diverse array of transactional applications. This talk will examine Oscar and the techniques it employs for deep customisation. Further, common patterns of robust e-commerce applications will be examined.

Transcript

1. oscar and the art of transactional django applications @codeinthehole David Winterbottom
3. Only special customers can see those products Sales reps can pay for multiple orders with one payment Sometimes you only pay tax on half a product!
7. + = +
9. E-commerce! • Products, baskets, orders, … • Everything can be customised • Could be added to your site
17. ❌ Tax ❌ Payment ❌ Shipping ❌ Fulfilment
19. Raison d'être • Make my life easier • Help Tangent be more efficient • Build complex, maintainable 
 e-commerce sites
20. My current platform is too slow My current platform won’t let me do X I hate my current platform!
21. Sweet spots • Marketplaces • Start-ups • B2B
23. product = Product.objects.get( upc=“9780981467306")
24. >>> product.price Decimal('22.60')
25. >>> strategy = selector.strategy(request) >>> info = strategy.fetch_for_product(
 product) >>> info.price.incl_tax
 Decimal(’22.60')
 >>> info.price.currency
 'GBP' >>> info.availability.message
 "In stock" >>> info.availability.is_available_to_buy
 True
26. Pluggable strategies • Multi-currency, multi-territory shops • Pluggable tax calculations • Per-customer pricing • …
27. Customisation
28. AUTH_USER_MODEL = ‘myapp.MyUser’ Replace user model 㱺
29. from django.db.models.loading import get_model Replace ANY model 㱺 class Meta: abstract = True +
30. from oscar.core.loading import get_class OrderCreator = get_class( 'order.utils', 'OrderCreator') Replace any CLASS 㱺
31. ⑂ ✍
32. URLS and views
33. from django.conf.urls import patterns, include from django.contrib import admin admin.autodiscover() urlpatterns = patterns('', (r'^admin/', include(admin.site.urls)), )
34. from django.conf.urls import patterns, include from django.contrib import admin admin.autodiscover() urlpatterns = patterns('', (r'^admin/', include(admin.site.urls)), )
35. class MyModelAdmin(admin.ModelAdmin): def get_urls(self): urls = super(MyModelAdmin, self).get_urls() my_urls = patterns('', (r'^my_view/$', self.my_view) ) return my_urls + urls
36. class MyModelAdmin(admin.ModelAdmin): def get_urls(self): urls = super(MyModelAdmin, self).get_urls() my_urls = patterns('', (r'^my_view/$', self.my_view) ) return my_urls + urls
37. from django.conf.urls import * from oscar.app import application urlpatterns = patterns('', url(r'', include(application.urls)) )
38. from django.conf.urls import * from oscar.app import application urlpatterns = patterns('', url(r'', include(application.urls)) )
39. from oscar.core.application import Application class Shop(Application): catalogue_app = get_class('catalogue.app', 'application') ... def get_urls(self): urls = [ url(r'^catalogue/', include(self.catalogue_app.urls)), ... ] return urls application = Shop()
40. from oscar.apps.checkout import app from . import views class CheckoutApplication(app.CheckoutApplication): # Replace a view class payment_details_view = views.PaymentDetailsView def get_urls(self): # Tinker with URLs etc ...
41. Oscar • For difficult e-commerce problems • Designed for flexibility • Anything can be customised • Customisation techniques drawn from Django itself
42. Lessons
43. Audit • “Why …?” • Log everything* • YPGNI • Audit models!
44. Audit models • An imported file • A request/response with 3rd party
45. from django.db import models class PartnerFeedFile(models.Model): filename = models.CharField(max_length=255) PENDING, PROCESSED, FAILED = ( 'Pending', 'Processed', 'Failed') STATUSES = ( (PENDING, PENDING), (PROCESSED, PROCESSED), (FAILED, FAILED), ) status = models.CharField( max_length=64, choices=STATUSES, default=PENDING) num_records = models.PositiveIntegerField() date_start_processing = models.DateTimeField(null=True) date_end_processing = models.DateTimeField(null=True)
47. from django.db import models class RequestResponse(models.Model): ... raw_request = models.TextField(max_length=512) raw_response = models.TextField(max_length=512) response_time = models.FloatField() date_created = models.DateTimeField( auto_now_add=True)
50. External transactions Digression:
51. DATABASES = { 'default': { ... 'ATOMIC_REQUESTS': True }, }
52. from django.db import transaction def external_api_call(request): # 1. Save something # 2. Make an API call and save audit # 3. Save something else
53. from django.db import transaction def external_api_call(request): Foo.objects.create(name="Before") with transaction.atomic(): # Make some external API call AuditModel.objects.create(...) Foo.objects.create(name="After")
54. DATABASES = { 'default': { ... 'ATOMIC_REQUESTS': True } } db = DATABASES['default'].copy() db['ATOMIC_REQUESTS'] = False DATABASE['autocommit'] = db
55. AuditModel.objects.using(‘autocommit’) \ .create(...)
56. Monitoring • 90% off all DVDs! • Application metrics • High and low thresholds
57. Tests? ✅ ✅ ✅ Docs? Metrics?
58. $ ./manage.py application_metric $name
59. Finance
62. Large (Django) projects
63. views.py
64. Boundaries • REST interface? • Never… • …modify a model field • …call save() dabapps.com/blog/django-models-and-encapsulation/
66. Pollution • Dirty/incomplete data • Anti-corruption layer • PAYMENT.dll
67. $ make project
68. CI examples github.com/tangentlabs /django-oscar /tangent-django-boilerplate
70. • github/django-oscar/django-oscar • v0.8, v1.0 • APIs • You?
71. @django_oscar @codeinthehole