VA DERS (Q: What does it say?) VA DERS VA DERS (A: Space - - PowerPoint PPT Presentation

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VA DERS (Q: What does it say?) VA DERS VA DERS (A: Space Invaders) am U us am U us (A: Ambiguous) convention configuration convention configuration (A: Convention over configuration) Welcome! A Grok T alk

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VA DERS

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(Q: What does it say?)

VA DERS

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VA DERS

(A: “Space Invaders”)

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am U us

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am U us

(A: “Ambiguous”)

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convention — configuration

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convention — configuration

(A: “Convention over configuration”)

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Welcome!

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A Grok T alk Brandon Craig Rhodes November 2007

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What's a convention?

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Conventions are traditionally extras.

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Conventions begin as

  • ptional practices to

keep code sane

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“We always capitalize the names of classes in the code we write for this department.”

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“If you have a class Foo, name its corresponding page template foo.pt.”

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“We're putting cover sheets

  • n all the TPS reports

before they go out.”

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What if ... ?

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What if your web framework used conventions rather than config files?

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A simple example:

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<html> <body> <h1>Title</h1> </body></html> index.pt <configure view=”index” class=”Index” template= “index.pt” /> app.config

View

“Index”

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<html> <body> <h1>Title</h1> </body></html> index.pt <configure view=”index” class=”Index” template= “index.pt” /> app.config

View

“Index”

A class you've written A page template you've written The configuration file you need to hook them up!

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Conventions are traditionally ignored by the computer

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But, what if ... ?

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What if the framework assumed, in the absence of

  • ther configuration, that

Index goes with index.pt?

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Result:

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<html> <body> <h1>Title</h1> </body></html> index.pt

View

“Index”

All explicit configuration has disapperaed

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Advantages Ensue!

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Advantages of CoC:

  • 1. Less repetition
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Advantages of CoC:

  • 1. Less repetition
  • 2. Conventions get used,

because they matter

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Advantages of CoC:

  • 1. Less repetition
  • 2. Conventions get used,

because they matter

  • 3. No loss of flexibility
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So, who does CoC?

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Actually a very old Computer Science concept

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Example: FORTRAN assumed, in the absence

  • f a declaration, that i

and j were integers, and that x and y were floating-point

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But when did it take off for web applications?

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2004

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Python frameworks: 2005 — Django, Turbogears 2006 — Pylons, Grok

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Q:

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Why talk about Grok?

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It's only a year old!

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Django and TurboGears are each two years old

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A:

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Because Grok is built atop Zope 3

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Zope 3 started in 2001, production release 2004

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Grok brings ease

  • f configuration to an

existing framework

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Zope 3 is more mature

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Zope 3 is powerful

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Zope 3 provides a powerful component framework

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But

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It requires configuration

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Raw Zope 3 requires you to use its Zope Configuration Markup Language (ZCML)

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<configure xmlns="http://namespaces.zope.org/zope" i18n_domain="zope" > <permission id="zope.Public" title="[public-permission] Public" description="Special permission indicating unconditional access. Public resources are always accessible." /> <utility component=".vocabulary.PermissionsVocabulary" name="Permissions" /> <utility component=".vocabulary.PermissionIdsVocabulary" name="Permission Ids" /> <include file="globalmodules.zcml" /> <include file="_protections.zcml" /> <utility provides=".interfaces.IAuthentication" component=".principalregistry.principalRegistry" />

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But not Grok!

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Grok is friendly

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More specifically

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Grok is a friendly cave man

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Grok wields a club

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In fact

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Grok wields a large club

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Grok uses his club to smash ZCML

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<configure xmlns="http://namespaces.zope.org/zope" i18n_domain="zope" > <permission id="zope.Public" title="[public-permission] Public" description="Special permission indicating unconditional access. Public resources are always accessible." /> <utility component=".vocabulary.PermissionsVocabulary" name="Permissions" /> <utility component=".vocabulary.PermissionIdsVocabulary" name="Permission Ids" /> <include file="globalmodules.zcml" /> <include file="_protections.zcml" /> <utility provides=".interfaces.IAuthentication" component=".principalregistry.principalRegistry" />

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Grok offers us his club

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So that our web apps can be configured using convention instead of XML

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Let's create a Grok instance!

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(Brandon, pause the slides, and show how to create a Grok instance. Name it “MyApp”.)

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The instance comes with a web page already displaying!

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What's the formula?

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Grok's Threefold Way

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Grok's Threefold Way

  • 1. An object at the URL
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Grok's Threefold Way

  • 1. An object at the URL
  • 2. A view for that object
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Grok's Threefold Way

  • 1. An object at the URL
  • 2. A view for that object
  • 3. A template for the view
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<html> <body> <h1>Title</h1> </body></html> index.pt <html><body> <h1>Welcome</h1> </body></html> http://.../index

View

“index”

Application Object

“MyApp”

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Let's add some more Python objects, more Grok Views, and more templates

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(Brandon, go add some models and further views to your application)

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<html>... <html>...</html> http://.../contents “index”

LOTR Application Object

“lotr” m m <html>... “contents” http://.../ <html>...</html>

Character

“Aragorn”

Battle

“Pelennor” <html>... “index” http://.../Aragorn/ <html>...</html> <html>... “index” http://.../Pelennor/ <html>...</html>

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Isn't that fun?

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Time for one more topic

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What should it be?

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There are several directions we could go

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I could show you how easy it is to process form data

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We could, in several seconds, have an XML-RPC interface to our models working

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We could explore how Zope can generate forms for you

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An illustration could be made of how our bare application logic itself benefits from being in a component framework

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But instead:

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We will look at the contract between a View and a Template

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And explore two forms that the contract can take

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Let's look back at our code...

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Our View classes are pretty anemic

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While our templates are out surfing our raw application objects!

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(Brandon, go show them your anemic View classes and your object-surfing templates)

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Let's call templates which surf the raw application objects “Muscular templates”

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Advantages of muscular templates:

  • 1. Quick
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Advantages of muscular templates:

  • 1. Quick
  • 2. Fast
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Advantages of muscular templates:

  • 1. Quick
  • 2. Fast
  • 3. Easy
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But...

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There are also disadvantages to muscular templates

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Disadvantages of muscular templates:

  • 1. Difficult to read
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Disadvantages of muscular templates:

  • 1. Difficult to read
  • 2. ... and thus, to audit
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Disadvantages of muscular templates:

  • 1. Difficult to read
  • 2. ... and thus, to audit
  • 3. They know your model
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The alternative:

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Muscular Views

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Let's return to our application's design

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And look at one

  • f its pages
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<html>... <html>...</html> http://.../contents “index”

LOTR Application Object

“lotr” m m <html>... “contents” http://.../ <html>...</html>

Character

“Aragorn”

Battle

“Pelennor” <html>... “index” http://.../Aragorn/ <html>...</html> <html>... “index” http://.../Pelennor/ <html>...</html>

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Character

“Aragorn” <html>... “index” http://.../Aragorn/ <html>...</html>

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The object and the view both have names in a traditional Zope page template...

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Character

“Aragorn” <html>... “index” http://.../Aragorn/ <html>...</html>

context

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Character

“Aragorn” <html>... “index” http://.../Aragorn/ <html>...</html>

context view

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But instead of using these default names, we can provide our own View namespace

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We do so by creating a namespace() method on

  • ur View
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(Brandon, go make your CharacterIndex View more muscular)

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What are the advantages of muscular Views?

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(Phrased differently: “Why on earth would you ever do that?!”)

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(Because, of course, we've added more code to our app without adding any new functionality!)

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Advantages:

  • 1. Your models can now evolve

without breaking your page templates

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Advantages:

  • 2. Page templates cannot

reveal data not delivered explicitly in namespace()

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Advantages:

  • 3. If you write some fake Views

returning static data from namespace(), your template writers can start work Day 1

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Advantages:

  • 4. Your Views are easy to test

(call namespace() and check result), templates are too (try them with static data)

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We'll conclude

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Grok

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Advantages:

  • 1. Easy, fun

2. 3. 4. 5.

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Advantages:

  • 1. Easy, fun
  • 2. Powerful framework

3. 4. 5.

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Advantages:

  • 1. Easy, fun
  • 2. Powerful framework
  • 3. Deploys with buildout

4. 5.

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Advantages:

  • 1. Easy, fun
  • 2. Powerful framework
  • 3. Deploys with buildout
  • 4. Shares code with Plone

5.

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Advantages:

  • 1. Easy, fun
  • 2. Powerful framework
  • 3. Deploys with buildout
  • 4. Shares code with Plone
  • 5. Vibrant community
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Of course, there are also disadvantages

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Disadvantages

  • 1. Not yet 1.0
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Disadvantages

  • 1. Not yet 1.0
  • 2. Security could be easier
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Disadvantages

  • 1. Not yet 1.0
  • 2. Security could be easier
  • 3. Online docs still weak

(buy PvW Zope 3 book!)

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Disadvantages

  • 1. Not yet 1.0
  • 2. Security could be easier
  • 3. Online docs still weak
  • 4. Community is 6h off
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Thank you! Any questions?