Powerful Generic Patterns With Django

POWERFUL GENERIC PATTERNSDjango's Content Types Framework

CONTENTTYPESAn application that can track all of the models installed in your Django-powered project, providing a high-level, generic interface for working with your models

SAY WHAT ?

CONTENTTYPES----------------------------------------| name | app_label | model || post | blogger | post || blog | blogger | Blog || like | likeable | Like |----------------------------------------

PROBLEMblog = Blog.objects.get( pk = 1 )posts = Post.objects.filter( blog = blog )features = Post.objects.filter( feature = True )

3+ URLs3+ view function3+ templates

PROBLEMblog = Blog.objects.get( pk = 1 )posts = Post.objects.filter( blog = blog )features = Post.objects.filter( feature = True )

{% for post in posts %}

{{ post.title }} {{ post.like_set.count }} likes

{% endfor %}

GENERIC VIEWS?

GENERIC VIEWS?

Take certain common idioms and patterns found in view development and abstract them so that you can quickly write common views of data without having to write too much code

GENERIC VIEWS?from django.views.generic import list_detail

def my_view( request ): return list_detail.object_list( queryset=Post.objects.all() )

NOT SO GENERIC VIEWSfrom django.views.generic import list_detail

def my_view( request ): return list_detail.object_list( queryset=Post.objects.all() )

NOT SO GENERIC VIEWS

NOT SO GENERIC VIEWS

• A Queryset• A Model + ID• A Model + Slug• A Model + Slug Field

To Use A Generic View You Need...

MORE PROBLEMSclass Post(models.Model): title = models.CharField() blog = models.ForeignKey( Blog ) body = models.TextField() slug = models.SlugField() likers = models.ForeignKey( User ) likes = models.IntegerField()

Blog

Post

Post LikesPost

Likers

MORE PROBLEMSclass Feature(models.Model): title = models.CharField() post = models.ForeignKey( Post )

likers = models.ForeignKey( User ) likes = models.IntegerField()

CONTENTTYPESAn application that can track all of the models installed in your Django-powered project, providing a high-level, generic interface for working with your models

CONTENTTYPESUse the ORM without knowing what kind of objects you might be working with.

CONTENTTYPESUse the ORM without knowing what kind of objects you might be working with.

EVER.

CONTENTTYPESYour Model

ContentType

Model A Model B Model C

GENERIC FOREIGNKEYfrom django.contrib.contenttypes.models import ContentType from django.contrib.contenttypes import generic

class Feature(models.Model): content_type = models.ForeignKey (ContentType) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey( 'content_type' ,'object_id' )

MAGIC BITS

class Feature(models.Model):

content_type = models.ForeignKey (ContentType)

object_id = models.PositiveIntegerField()

content_object = generic.GenericForeignKey( 'content_type' ,'object_id' )

GENERIC FOREIGNKEY>>> obj = Feature.objects.get( pk = 1 )>>> obj.content_object>>> <Post: Hello World>

>>> obj = Feature.objects.get( pk = 2 )>>> obj.content_object>>> <Blog: The Best Blog>

>>> obj = Feature.objects.get( pk = 3 )>>> obj.content_object>>> <Anything: Whatever You Want>

GENERIC FOREIGNKEY

GENERIC FOREIGNKEYclass Post(models.Model): title = models.CharField() blog = models.ForeignKey( Blog ) body = models.TextField() slug = models.SlugField()

class Like( models.Model ): content_type = models.ForeignKey( ContentType ) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey( ... ) likers = models.ManyToMany( User )

GOTCHA!

Models are NOT aware of their Content Type

MORE PROBLEMSclass Like( models.Model ): content_type = models.ForeignKey( ContentType ) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey( ... ) likers = models.ManyToMany( User )

MORE PROBLEMS

def like_view( request, object_id ): post = Post.objects.get( pk = object_id ) like = Like( object_id = post, ??? )

class Like( models.Model ): content_type = models.ForeignKey( ContentType ) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey( ... ) likers = models.ManyToMany( User )

GENERIC GEMSfrom django.contrib.contenttypes.models import ContentTypefrom django.contrib.auth.models import User

>>> type = ContentType.objects.get_for_model( User )>>> type>>> <ContentType: user >

>>> model = type.model_class()>>> model>>> <class: 'django.contrib.auth.models.User'>

GENERIC GEMS

PATTERN #1

PATTERN #1Self-Aware Model

SELF AWARE MODELclass SelfAwareModel(models.Model): def get_ct( self ): ''' Returns the Content Type for this instance''' return ContentType.objects.get_for_model(self)

def get_ct_id( self ): ''' Returns the id of the content type for this instance''' return self.get_ct().pk

def get_app_label( self ): return self.get_ct().app_label

def get_model_name( self ): return self.get_ct().model

class Meta: abstract = True






CACHED BY DJANGO






CACHED BY DJANGO

self.__class__._cache[self.db][key]

SELF AWARE EVERYTHINGclass Post( SelfAwareModel ): title = models.CharField() blog = models.ForeignKey( Blog ) body = models.TextField() slug = models.SlugField()




ALL MODELSSUBCLASSE

SELFAWAREMODEL



@permalink def get_absolute_url( self ): ...

>>> post = Post.objects.latest()>>> obj.get_ct()>>> <ContentType: post>



@permalink def get_absolute_url( self ): ...

>>> post = Post.objects.latest()>>> obj.get_ct()>>> <ContentType: post>

I KNOW MYCONTENT TYPE

HOORAY!

PATTERN #2REAL Generic Views

REAL GENERIC VIEW

def object_list( request, ct_id ... ): type = ContentType.objects.get( pk = ct_id ) model = type.model_class() obj_list = model._default_manager.all()

return render_to_response( ... )

REAL GENERIC VIEW

def object_detail( request, ct_id, obj_id, template=None ): type = ContentType.objects.get( pk = ct_id ) model = type.model_class() obj = model._default_manager.get( pk = ct_id )

if template is None: template = '%s_detail.html'%(type) return render_to_response( template )



REAL GENERIC VIEW

Might Want To Cache That



REAL GENERIC VIEW

Might Want To Cache That

• self.__class__._cache[self.db][key]• cPickle & noSQL DB ( Redis )

REAL GENERIC VIEWproject|| - likeables/|| - blog/ | |- templates/ | |- blog/ | -post_list.html | -post_detail.html | -urls.py|| - templates/| - object_list.html| - object_detail.html| - urls.py

MORE PROBLEMS

Blog

Post

Post LikesPost

Likers

MORE PROBLEMS

Blog

Post

Post LikersPost Likes

LESS PROBLEMSLIKE

ContentType

POST FEATURE ANYTHING

LIKE ANYTHING YOU WANT

NOT BAD, KID!

PATTERN #3Universal URLs

UNIVERSAL URLsurlpatterns = patterns( 'myproj.myapp', url( r'^(?P<slug>[-\w]+)/(?P<ct_id>\d+)/list/$', 'object_list', name='my_proj_content_list' ), url( r'^(?P<slug>[-\w]+)/(?P<ct_id>\d+)-(?P<obj_id>\d+)/$', 'object_detail', name="my_proj_content_detail" ), url( r'^(?P<slug>[-\w]+)/(?P<ct_id>\d+)-(?P<obj_id>\d+)/edit/$', 'object_edit', name="my_proj_content_edit" ) ...)

UNIVERSAL URLs/something-here/23/list/

/some-title/23-21/

/some-title/23-21/edit/

/some-title/23-21/delete/

/some-title/23-21/blah/

PATTERN #4Magic Forms

MAGIC FORMS

def edit_object( request, ct_id, obj_id ): obj = utils.get_object( ct_id, obj_id )

MAGIC FORMS


form = ???

MAGIC FORMS


form = ???

Can't predefine ModelForm when you don't know what model you're working with

MAGIC FORMS

MAGIC FORMSdef form_class_for( obj, includes=[] excludes=[] ): modelclass = obj.get_ct().model_class()

class _MagicForm(forms.ModelForm): ... class Meta: model= modelclass if includes: fields = includes if excludes: exclude = excludes

return _MagicForm



return _MagicForm

DON'T KNOW



return _MagicForm

DON'TCARE


class _MagicForm(forms.ModelForm): ... class Meta: model= modelclass

if includes: fields = includes if excludes: exclude = excludes

return _MagicForm PERFECTLYLEGAL

FULL CIRCLE


formclass = utils.get_form_for( obj )

form = formclass()

return render_to_response( ... {'form':form} )

FULL CIRCLE



form = formclass()


DON'T KNOW

FULL CIRCLE



form = formclass()


DON'TCARE

DEAD SIMPLE{% url my_proj_content_list ct_id=obj.get_ct_id %}

{% url my_proj_content_detail slug=obj.slug, ct_id=obj.get_ct_id, obj_id=obj.pk %}

{% url my_proj_content_edit slug=obj.slug, ct_id=obj.get_ct_id, obj_id=obj.pk %}

FOR THE WIN

SCALE IT OUT

1.Define A Model2.Sync DB3.Make A Template ( Maybe ? )4.Rinse 5.Repeate

PATTERNS RECAP

• Self Aware Models• Better Generic Views & utilities• Universial URLs• Magic Forms

PATTERNS RECAP

• Self Aware Models• Better Generic Views & utilities• Universial URLs• Magic Forms

You can perform CRUD ops and create any kind of relationship on any kind of object at anytime without programming for every situation.

Powerful Generic Patterns With Django

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