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
   

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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!
   

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7. +
   =
   +
   

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9. E-commerce!
   • Products, baskets, orders, …
   • Everything can be customised
   • Could be added to your site
   

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17. ❌ Tax
    ❌ Payment
    ❌ Shipping
    ❌ Fulfilment
    
    

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19. Raison d'être
    • Make my life easier
    • Help Tangent be more efficient
    • Build complex, maintainable 

    e-commerce sites
    

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20. 
    My current platform is too slow
    My current platform won’t
    let me do X
    
    
    I hate my current platform!
    

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21. Sweet spots
    • Marketplaces
    • Start-ups
    • B2B
    

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23. product = Product.objects.get(
    upc=“9780981467306")
    

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24. >>> product.price
    Decimal('22.60')
    

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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
    

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26. Pluggable strategies
    • Multi-currency, multi-territory shops
    • Pluggable tax calculations
    • Per-customer pricing
    • …
    

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27. Customisation
    

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28. AUTH_USER_MODEL = ‘myapp.MyUser’
    Replace user model
    㱺
    

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29. from django.db.models.loading import get_model
    Replace ANY model
    㱺
    class Meta:
    abstract = True
    +
    

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30. from oscar.core.loading import get_class
    OrderCreator = get_class(
    'order.utils', 'OrderCreator')
    Replace any CLASS
    㱺
    

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31. ⑂ ✍
    

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32. URLS
    and
    views
    

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33. from django.conf.urls import patterns, include
    from django.contrib import admin
    admin.autodiscover()
    urlpatterns = patterns('',
    (r'^admin/', include(admin.site.urls)),
    )
    

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34. from django.conf.urls import patterns, include
    from django.contrib import admin
    admin.autodiscover()
    urlpatterns = patterns('',
    (r'^admin/', include(admin.site.urls)),
    )
    

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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
    

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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
    

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37. from django.conf.urls import *
    from oscar.app import application
    urlpatterns = patterns('',
    url(r'', include(application.urls))
    )
    

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38. from django.conf.urls import *
    from oscar.app import application
    urlpatterns = patterns('',
    url(r'', include(application.urls))
    )
    

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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()
    

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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
    ...
    

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41. Oscar
    • For difficult e-commerce problems
    • Designed for flexibility
    • Anything can be customised
    • Customisation techniques drawn
    from Django itself
    

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42. Lessons
    

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43. Audit
    • “Why …?”
    • Log everything*
    • YPGNI
    • Audit models!
    

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44. Audit models
    • An imported file
    • A request/response with 3rd party
    

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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)
    

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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)
    

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50. External
    transactions
    Digression:
    

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51. DATABASES = {
    'default': {
    ...
    'ATOMIC_REQUESTS': True
    },
    }
    

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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
    

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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")
    

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54. DATABASES = {
    'default': {
    ...
    'ATOMIC_REQUESTS': True
    }
    }
    db = DATABASES['default'].copy()
    db['ATOMIC_REQUESTS'] = False
    DATABASE['autocommit'] = db
    

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55. AuditModel.objects.using(‘autocommit’) \
    .create(...)
    

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56. Monitoring
    • 90% off all DVDs!
    • Application metrics
    • High and low thresholds
    

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57. Tests?
    ✅
    ✅
    ✅
    Docs?
    Metrics?
    

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58. $ ./manage.py application_metric $name
    

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59. Finance
    

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62. Large (Django) projects
    

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63. views.py
    

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64. Boundaries
    • REST interface?
    • Never…
    • …modify a model field
    • …call save()
    dabapps.com/blog/django-models-and-encapsulation/
    

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66. Pollution
    • Dirty/incomplete data
    • Anti-corruption layer
    • PAYMENT.dll
    

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67. $ make project
    

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68. CI examples
    github.com/tangentlabs
    /django-oscar
    /tangent-django-boilerplate
    

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70. • github/django-oscar/django-oscar
    • v0.8, v1.0
    • APIs
    • You?
    

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71. @django_oscar
    @codeinthehole
    

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