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Writing a Django e-commerce framework David Winterbottom @codeinthehole
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Synopsis • Background / challenges • Why django / python • Customising django apps • E-commerce tips
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Background
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• 5 years of e-commerce projects • PHP / Python / Django • Lots of war stories
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Books
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Bookshop domain • Millions of products • ISBNs, BIC categories, authors, publishers • Automated feed-driven processing • Catalogue • Stock • Rich data
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Two tier structure • Application tier - serves HTTP requests • Processing tier • Download and import feeds • Data cleaning and processing
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More books
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Different... • Fulfilment partners • Stock logic • Payment partners • Multiple payment sources • Complicated offers • eBooks!
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PHP framework • Customisation via include path overrides • Lots of duplication • Hard to upgrade • Not-invented-here syndrome
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Nailvarnish
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T-shirts
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Digital music
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Bar equipment
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New requirements • Product variations - colours, sizes etc • New fulfilment processes • Pricing models
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B2B • Sales reps • Tax rules • Managed budgets • Integration with “enterprise” software
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• Original assumptions all broken • Domains vary wildly • Lots of work-arounds
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Requirements • Agnostic - few assumptions as possible • Models domain • without duplication • without too much meta-data
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EAV ENTITY ATTRIBUTE VALUE Product Weight 150 Order Cost centre ZPAN
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• Leather gloves
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Bendy bits
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Taxonomy
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Stock
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Shipping
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Payment
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and also...
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Nothing is sacred
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django-oscar • Django 1.3 • Experience of last 5 years baked into models • Lean core • Different customisation path
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Lots of others • Satchmo • Lightning-Fast-Shop • Satchless • Django-shop • Plata, Mamona, Cartridge, ... • http://djangopackages.com/grids/g/ecommerce/
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Decimals
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kwargs
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Shipping calculator
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PHP
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Python
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Web framework • Well-thought out structure • Templating, HTTP, caching, ... • Good test support • Security • Class-based views
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Models • Models drive the design • Capture domain logic • Foundation for rest of application
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Eco-system • Haystack (search) • South (database migrations) • Celery (job queue) • Internal libraries
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Customisation
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Techniques
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DEBUG = True settings.py
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AUTH_PROFILE_MODULE = ‘customer.Profile’ settings.py
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Key idea • Having the same name/identifier as your parent • Subclass and override
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Templates
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Django looks here first
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Views
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Oscar default
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urls.py
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oscar/app.py
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oscar/core/app.py
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oscar/apps/checkout/app.py
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Oscar project
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Replace application urls.py
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myproject/app.py Use different app instance
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myproject/checkout/app.py Use different view classes
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myproject/checkout/views.py Override and extend method
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Models
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Oscar default
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settings.py
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abstract_models.py
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models.py
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Oscar project
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replaces oscar app settings.py same ‘app label’
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add custom fields myproject/voucher/models.py import remaining models
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templatetags management commands fixtures settings.py
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Classes
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model name ‘app label’
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module path class name
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use same class name as in core
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Recap • Bit of a work-around... • ...but works well • Applicable to other django libraries
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Best practices
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Log everything ...except bankcard details.
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Audit models
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Monitor everything watch high and low thresholds
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SOA • Services make your life easier • Keep a layer in front of your models • Facade design pattern
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View
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View Models Database Load business objects
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View Service Models Database Load business objects Business logic here
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View Service Models Database Load business objects Business logic here
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View Service Models Database Load business objects Business logic here
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Rules of thumb • Keep views lean • Business logic in: • Models • Services • Validation logic in forms
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Danger
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Domain pollution • When integrating with a 3rd party... • they will try and push their shortcomings into your platform
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Anti-corruption layer Your platform Their platform Anti-corruption layer
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Summary • Django e-commerce is an emerging force • Customising django apps isn’t easy • Oscar’s future: • NoSQL • Table inheritance
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Image credits Books: http://www.flickr.com/photos/th3ph17/3091294342/ More books: http://www.flickr.com/photos/cheryl-j/3965942320/ Nail varnish: http://www.flickr.com/photos/greenzowie/5451402463/ Leather gloves: http://www.flickr.com/photos/theopenseas/175598276/ Lego shipping: http://www.flickr.com/photos/lydiashiningbrightly/5356210011/ Rubber gloves: http://www.flickr.com/photos/recyclethis/139373445/ Warehouse: http://www.flickr.com/photos/23748404@N00/15648677/ Taxonomy: http://www.flickr.com/photos/kqedquest/831547339/ T-shirts: http://www.flickr.com/photos/blazerman/177165473/