plone: event driven programming
DESCRIPTION
A talk I gave at the European Plone Symposium 2010 in Sorrento. Event Driven Programming in Plone - or how to extend Plone the lazy way Ever wanted to extend Plone somehow but not wanted to change the existing code for a product? Want to learn the easy way to extend Plone's functionality? Events! I will show you some examples of how to use Plone's event subscriber and workflow systems to extend Plone without having to change any existing products. Using a number of common Plone products and the events system to combine them you can come up with unlimited possibilities. I'll use examples from two websites I've been working on recently to show you how you can make authors have to pay (using GetPaid) to publish content on a site, and how to check the comments are not spam on your discussion board.TRANSCRIPT
Matt Hamilton
...or how to extend Plone the lazy way
Event Driven Programming in Plone
Matt HamiltonTechnical Director, Netsight
Matt Hamilton European Plone Symposium 2010, Sorrento
Who am I?
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- Matt Hamilton
- Technical Director of Netsight Internet Solutions
- A Plone ‘integrator’
@hammertoe
Matt Hamilton European Plone Symposium 2010, Sorrento
Who is this talk for?
- Integrators
- Those newish to Plone, they can assemble together a site from a number of products, but don't really want to alter them
- I consider myself 'experienced' but this was a bit of an epiphany for me
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Matt Hamilton European Plone Symposium 2010, Sorrento
What is the problem?
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?
Matt Hamilton European Plone Symposium 2010, Sorrento
What is the problem?
I want to change the functionality of an existing product, but don't want to change the guts of it.
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Matt Hamilton European Plone Symposium 2010, Sorrento
What is the problem?
Came from a real life problem. Developing Netsight's new website. Wanted to use plone.app.discussion, but needed to add spam checking on comments
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Matt Hamilton European Plone Symposium 2010, Sorrento
What is the problem?
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Matt Hamilton European Plone Symposium 2010, Sorrento
What is the problem?
plone.app.discussion has captcha support already, but I wanted to add Akismet support, but no easy extension point
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Matt Hamilton European Plone Symposium 2010, Sorrento
Admittedly, I could have offered to refactor the whole p.a.discussion code ;)
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Matt Hamilton European Plone Symposium 2010, Sorrento
Considered Approaches
- I could subclass the product and override it
➡ A lot of boiler-plate for small change
- I could use an adapter and adapt the behaviour
➡ No adapter lookup where I needed it
- I could 'just hack it in the original code'
➡ Yuck! Maintainability nightmare
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Matt Hamilton European Plone Symposium 2010, Sorrento 11
Eureka!
Matt Hamilton European Plone Symposium 2010, Sorrento
Eureka!
Use Events!
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Matt Hamilton European Plone Symposium 2010, Sorrento
Eureka!
- I realised I could leave p.a.discussion alone, and just listen for an event for when a comment is added and then check it for spam
- I can listen for an event from Plone and then do the behaviour afterwards
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Matt Hamilton European Plone Symposium 2010, Sorrento
Advantages
- Leave the existing code alone
- Work around lack of suitable extension point
- Very little boilerplate code
- All happens in same transaction still
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Matt Hamilton European Plone Symposium 2010, Sorrento
Zope's Event System
- Events
- Subscribers
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Matt Hamilton European Plone Symposium 2010, Sorrento
A Simple Event
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in configure.zcml:
<subscriber for=".interfaces.IMyObject .interfaces.IMyEvent" handler=".events.myEventHandler" />
in events.py:
def myEventHandler( object, event): object.doSomeThing()
Matt Hamilton European Plone Symposium 2010, Sorrento
Event Simpler Event
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in events.py:
from five import grokfrom interfaces import IMyObject, IMyEvent
@@grok.subscribe(IMyObject, IMyEvent)def myEventHandler( object, event): object.doSomeThing()
Matt Hamilton European Plone Symposium 2010, Sorrento
Example - Spam Checking
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in events.py:
from five import grokfrom plone.app.discussion.interfaces \ import ICommentfrom zope.lifecycleevent.interfaces \ import IObjectAddedEvent
@@grok.subscribe(IComment, IObjectAddedEvent)def checkForSpam( comment, event): wf = getToolByName(comment, 'portal_workflow') if is_spam(comment.text): wf.doActionFor(comment, ‘spam’)
Matt Hamilton European Plone Symposium 2010, Sorrento
Next Example - GetPaid
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GetPaid is an eCommerce add-on to Plone
➡ Allows you to mark any piece of content as ‘buyable’
Matt Hamilton European Plone Symposium 2010, Sorrento
PloneConf 2010 Registration
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User clicks ‘register’
User fills in ‘add attendee’ form, and hits submit
Event fired indicating object added to container
Event subscriber marks item as buyable, adds to shopping cart, and then redirects to cart view
Matt Hamilton European Plone Symposium 2010, Sorrento
GetPaid Example
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from Products.CMFCore.utils import getToolByNamefrom getpaid.core.interfaces import workflow_statesimport interfaces
def handlePaymentReceived( order, event ):
if event.destination !=workflow_states.order.finance.CHARGED: return for item in order.shopping_cart.values(): ob = item.resolve() workflow = getToolByName( ob, 'portal_workflow') state = workflow.getInfoFor( ob, 'review_state' ) if state == 'published': return workflow.doActionFor( ob, 'publish')
Matt Hamilton European Plone Symposium 2010, Sorrento
Other Ideas
- Whenever a Folder is created, add some default content to it
- When a Page is added, set some metadata fields
- When an Event is added, check that an expiry date has been set no more than 12 months in the future
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