Rethinking the Reusable Apps

8/8/2019 Rethinking the Reusable Apps

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Rethinking the Reusable

Application ParadigmAlex Gaynor

Monday, September 6, 2010


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I work here.Monday, September 6, 2010


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I work with these guys.Monday, September 6, 2010


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We do a lot of this.Monday, September 6, 2010


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You have been sold alie!



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By this man!Monday, September 6, 2010


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The dangerous lie:

defmy_view(request, pk, template_name="my_app/my_page.html", form_class=MyForm,

redirect_url="/home/place/"):

# magical view stuff here return HttpResponse()

This does not, a reusable app, make.



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That doesnt mean its useless.

But it doesnt solve all the problems.What the hell are the problems were trying to solveanyways?



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Similar patterns across many sites (tagging, voting,commenting, etc.).

Write once, use everywhere.

No need to reinvent the wheel.

Why Reusable Apps?



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The problems.

Differing business logic.

Everyone wants comments, but can anonymous userscomment, is there a comment preview page?

Differing data storage

Does a forum belong to a group, does it need a slug? Docategories have an icon?



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The Solutions



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Class based views

See Ben Firshman at 2:20: Alternate ViewsSimple view functions dont provide entry points forchanging logic, besides what you create a parameter for.

Subclass to change the logic, e.g. the admin.



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django.contrib.admin

classArticleAdmin(admin.ModelAdmin):

defsave_model(self, request, obj, form, change):

obj.user = request.userobj.save()

Theres like 30 of these.



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Do Less

aka: reusable frameworksCreate a framework, so other people can write their buisnesslogic around it.

Example: badges.



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Badges

Can badges have multiple levels?How do you know if a user has received a given badge, at agiven level?

Can a user receive a badge more than once?



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The stuff everyone needs...

Templatetags for getting badge count or list of badges for auser.

Queueing of computations, when theyre expensive.

Persistence.



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brabeionclassPointsBadge(Badge):

slug ="points"

levels = [

"Bronze",

"Silver",

"Gold",

]events = [

"points_awarded",

]

multiple =False

defaward(self, user, **state):

points = user.profile.points

if points >10000:

return BadgeAwarded(level=3)

elif points >7500:


elif points >5000:




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Be flexible

You cant predict all the ways people want to use yoursoftware.

But you know what the common way is (probably whatever

you wanted to do in the first place).So provide a default, but let people swap it out.



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django-taggit

classEvent(models.Model):

title = models.CharField(max_length=100)

date = models.DateField()

tags = TaggableManager()

Common case: I want some tags on my stuff.



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Uncommon cases

Non-integer primary keys (IntegerField for the

GenericForeignKey, by default)

Per-user tags.

Official tags.Custom caching managers, or anything else.



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classEventTaggedItems(BaseTaggedItem):

event = models.ForeignKey("Event")

classEvent(models.Model):

title = models.CharField(max_length=100, primary_key=True)

date = models.DateField()

tags = TaggableManager(through=EventTaggedItems)

Swap out the intermediary model (also the Tag model)



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Custom backends

django-registration

django.core.cache

django.contrib.auth

django.core.files

django.contrib.sessions



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django-registrationclassSimpleBackend(object): defregister(self, request, **kwargs):

username, email, password = kwargs['username'], kwargs['email'], kwargs['password1']

User.objects.create_user(username, email, password)

# authenticate() always has to be called before login(), and

# will return the user we just created.

new_user = authenticate(username=username, password=password)

login(request, new_user)

signals.user_registered.send(sender=self.__class__,user=new_user,

request=request)

return new_user

defactivate(self, **kwargs):

raiseNotImplementedError

defregistration_allowed(self, request):

returngetattr(settings, 'REGISTRATION_OPEN', True)

defget_form_class(self, request):

return RegistrationForm

defpost_registration_redirect(self, request, user):

return (user.get_absolute_url(), (), {})

defpost_activation_redirect(self, request, user):

raiseNotImplementedError



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Libraries

Not everything is business logic

Tools for other people

e.g.: django.forms



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django-filtersclassProductFilterSet(django_filters.FilterSet):

classMeta:

model = Product

fields = ['name', 'price', 'manufacturer']

Create filters like the admins list_filter.Built on top of django.forms



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Other Tools

django-fixture-generator

Generate fixtures programatically.django-templatetag-sugar

A declarative API for creating templatetags.

django_compressor

Compress and combine static media (CSS + JS)



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When to ignore all ofthis



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Well defined problem spaces.

Extremely common use cases.

You just dont care about the 20% (internal apps?)



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user_messages

Internal Eldarion app

Allows user to send messages to other users.

Almost no customizability.

Only control is to enable multi-user messaging or not.

Dead simple to use.



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0 flexibility, 0 work

Add to INSTALLED_APPSAdd to urls.py

Write templates.

Done.



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Questions?

http://alexgaynor.net
http://alexgaynor.net/http://alexgaynor.net/http://alexgaynor.net/

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Rethinking the Reusable Apps