Writing a Django e-commerce framework

From OSCON 2012. This presentation discusses the reasons for writing an e-commerce framework and details a number of techniques for customising Django apps.

Transcript

1. Writing  a  Django  
   e-­‐commerce  
   framework
   OSCON  2012
   Friday, 20 July 12
   

   View Slide

2. Me
   •David  Winterbottom  /  @codeinthehole
   •Tangent  Labs,  London
   •Head  of  E-­‐commerce  team
   •Python  hacker
   •commandlinefu.com,  django-­‐oscar
   Friday, 20 July 12
   

   View Slide

3. Synopsis
   •Motivation
   •Oscar  -­‐  what  problem  does  it  solve?
   •Design  decisions  -­‐  customisation  techniques
   •E-­‐commerce  tips/advice
   Friday, 20 July 12
   

   View Slide

4. Motivation
   Friday, 20 July 12
   

   View Slide

5. •5  years  of  e-­‐commerce  projects
   •PHP  =>  Python  /  Django
   •Lots  of  war  stories
   Tangent  Labs
   Friday, 20 July 12
   

   View Slide

6. Books
   Friday, 20 July 12
   

   View Slide

7. Bookshop  domain
   •Millions  of  products
   •ISBNs,  BIC/BISAC  categories,  authors,  publishers
   •Automated  feed-­‐driven  processing
   •Catalogue
   •Stock
   •Rich  data
   Friday, 20 July 12
   

   View Slide

8. Two  tier  structure
   •Application  tier  -­‐  serves  HTTP  requests
   •Processing  tier:
   •Download  and  import  feeds
   •Data  cleaning  and  processing
   •Periodic  jobs  for  fulfilment
   Friday, 20 July 12
   

   View Slide

9. Variations
   •New  fulfilment  partners
   •Stock/availability  logic
   •Multiple  payment  partners
   •Split-­‐payment  sources
   •Multibuy  offers,  vouchers
   •eBooks!
   Friday, 20 July 12
   

   View Slide

10. PHP  framework
    •Home-­‐rolled  web  framework
    •Customisation  via  include  path  overrides
    •Lots  of  duplication
    •Hard  to  upgrade
    Friday, 20 July 12
    

    View Slide

11. Nailvarnish
    Friday, 20 July 12
    

    View Slide

12. T-­‐shirts
    Friday, 20 July 12
    

    View Slide

13. Digital  music
    Friday, 20 July 12
    

    View Slide

14. Bar  equipment
    Friday, 20 July 12
    

    View Slide

15. New  requirements
    •Product  variations  -­‐  colours,  sizes  etc
    •New  fulfilment  processes:  
    •webservices  /  warehouses
    •Per-­‐customer  prices
    Friday, 20 July 12
    

    View Slide

16. B2B
    •Sales  reps,  customer  hierarchies
    •Tax  rules
    •Managed  budgets
    •Integration  with  “enterprise”  partners
    Friday, 20 July 12
    

    View Slide

17. •Original  assumptions  all  broken
    •Domains  vary  wildly
    •Lots  of  work-­‐arounds
    Friday, 20 July 12
    

    View Slide

18. Oscar
    Friday, 20 July 12
    

    View Slide

19. Requirements
    •Lean  -­‐  as  few  assumptions  as  possible
    •Models  domain  
    •without  duplication
    •without  too  much  meta-­‐data
    Friday, 20 July 12
    

    View Slide

20. Friday, 20 July 12
    

    View Slide

21. Domain  modelling
    •Implementation  deeply  
    connected  to  core  business  
    concepts
    •“...where  powerful  new  
    features  unfold  as  corollaries  to  
    older  features.”
    Friday, 20 July 12
    

    View Slide

22. Friday, 20 July 12
    

    View Slide

23. Lots  of  others
    •Satchmo  
    •Lightning-­‐Fast-­‐Shop
    •Satchless
    •Django-­‐shop
    •Plata,  Mamona,  Cartridge,  ...
    •http://djangopackages.com/grids/g/ecommerce/
    Friday, 20 July 12
    

    View Slide

24. Design  decisions
    Friday, 20 July 12
    

    View Slide

25. Python
    •Decimal  support
    •**kwargs
    •Mixins
    Friday, 20 July 12
    

    View Slide

26. Friday, 20 July 12
    

    View Slide

27. Web  framework
    •Well-­‐thought  out  structure
    •Templating,  HTTP,  security,  caching,  ...
    •Class-­‐based  views
    Friday, 20 July 12
    

    View Slide

28. Models
    •Models  drive  the  design
    •Capture  domain  logic
    •Foundation  for  rest  of  application
    Friday, 20 July 12
    

    View Slide

29. Eco-­‐system
    •Haystack  (search)
    •South  (database  migrations)
    •Celery  (job  queue)
    •Internal  libraries
    Friday, 20 July 12
    

    View Slide

30. Customisation
    Friday, 20 July 12
    

    View Slide

31. DEBUG = True
    settings.py
    Friday, 20 July 12
    

    View Slide

32. AUTH_PROFILE_MODULE =
    ‘customer.Profile’
    settings.py
    Friday, 20 July 12
    

    View Slide

33. Different  approach
    •Key  idea:
    •Having  the  same  name/identifier  as  your  parent  
    •Subclass  and  override
    Friday, 20 July 12
    

    View Slide

34.  Templates
    Friday, 20 July 12
    

    View Slide

35. Friday, 20 July 12
    

    View Slide

36. TEMPLATE_LOADERS = (
    'django.template.loaders.filesystem.Loader',
    'django.template.loaders.app_directories.Loader',
    )
    TEMPLATE_DIRS = (
    '/var/www/project/templates/',
    )
    Replace
    Friday, 20 July 12
    

    View Slide

37. TEMPLATE_LOADERS = (
    'django.template.loaders.filesystem.Loader',
    'django.template.loaders.app_directories.Loader',
    )
    TEMPLATE_DIRS = (
    '/var/www/project/templates/'
    '/path/to/oscar/',
    )
    Override
    parent  of  Oscar’s  
    template  directory
    Friday, 20 July 12
    

    View Slide

38. # base.html
    {% extends 'templates/base.html' %}
    {% block scripts %}
    
    {% endblock %}
    Override
    Friday, 20 July 12
    

    View Slide

39. # base.html
    {% extends 'templates/base.html' %}
    {% block scripts %}
    
    {{ block.super }}
    {% endblock %}
    Extend
    Friday, 20 July 12
    

    View Slide

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
    Friday, 20 July 12
    

    View Slide

41. Apps
    Friday, 20 July 12
    

    View Slide

42. from django.db.loading import get_model
    Line = get_model('basket', 'Line')
    Dynamic  loading  1
    INSTALLED_APPS = (
    'oscar.apps.basket'
    )
    Friday, 20 July 12
    

    View Slide

43. from django.db.loading import get_model
    Line = get_model('basket', 'Line')
    Dynamic  loading  1
    INSTALLED_APPS = (
    'oscar.apps.basket'
    )
    ‘App  label’
    Friday, 20 July 12
    

    View Slide

44. INSTALLED_APPS = (
    'oscar',
    'oscar.apps.catalogue',
    'oscar.apps.basket',
    'oscar.apps.checkout',
    'oscar.apps.order',
    ...
    )
    Friday, 20 July 12
    

    View Slide

45. INSTALLED_APPS = (
    'oscar',
    'oscar.apps.catalogue',
    'myproject.basket',
    'oscar.apps.checkout',
    'oscar.apps.order',
    ...
    )
    Same  app  label  as  
    parent  app
    Friday, 20 July 12
    

    View Slide

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 *
    Friday, 20 July 12
    

    View Slide

47. INSTALLED_APPS = (
    'oscar',
    'oscar.apps.catalogue',
    'oscar.apps.basket',
    'oscar.apps.checkout',
    'oscar.apps.order',
    ...
    )
    templatetags
    management  commands
    Friday, 20 July 12
    

    View Slide

48. Recap
    •App  label    is  the  ID
    •Models  can  overridden  and  extended
    Friday, 20 July 12
    

    View Slide

49. from oscar.core.loading import get_class
    OrderCreator = get_class('order.utils', 'OrderCreator')
    Dynamic  loading  2
    Friday, 20 July 12
    

    View Slide

50. # order/utils.py
    from oscar.apps.order.utils import OrderCreator as \
    CoreOrderCreator
    class OrderCreator(CoreOrderCreator):
    def allocate_stock(self, line):
    # Override/extend method
    ...
    Friday, 20 July 12
    

    View Slide

51. Recap
    •(App  module,  class  name)    is  the  ID
    •Any  class  can  be  overridden  or  extended
    Friday, 20 July 12
    

    View Slide

52. Tips  and  advice
    Friday, 20 July 12
    

    View Slide

53. Log  everything
    ...except  sensitive  customer  details.
    Friday, 20 July 12
    

    View Slide

54. Audit  models
    Friday, 20 July 12
    

    View Slide

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)
    Friday, 20 July 12
    

    View Slide

56. •High  and  low  thresholds
    •It’s  always  your  fault  when  things  go  wrong
    Monitor  everything
    Friday, 20 July 12
    

    View Slide

57. Service  layers
    •Avoid  views  talking  to  your  models  directly
    •See  ‘Facade’  design  pattern
    •Anti-­‐corruption  layers
    Friday, 20 July 12
    

    View Slide

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
    Friday, 20 July 12
    

    View Slide

59. Summary
    •Django  is  great  for  modelling  complex  domains
    •Writing  customisable  django  apps  isn’t  easy
    •Oscar’s  future:  
    •NoSQL  -­‐  no  more  EAV
    Friday, 20 July 12
    

    View Slide

60. Image  credits
    Books:
    http://www.flickr.com/photos/th3ph17/3091294342/
    Nail varnish:
    http://www.flickr.com/photos/kqedquest/831547339/
    T-shirts:
    http://www.flickr.com/photos/blazerman/177165473/
    Friday, 20 July 12
    

    View Slide