Notes On Django

Use virtual env -- easy to manage different python/django versions:

$ virtualenv  -p /usr/bin/python2.7  /opt/penv/p2
$ . /opt/penv/p2/bin/activate

Install django within virtual env :

$ pip freeze   # output is empty -- no additional modules.
$ pip install Django==1.6.10        # Latest GA is Django==1.7.5
$ pip install mysqlclient==1.3.6    
$ pip install djangorestframework==3.1.0
$ pip install django-rest-swagger   # Used for auto generation of /docs
$ pip freeze   # installed django modules is displayed.

Create new django project:

$ which django-admin.py
   /opt/penv/p2/bin/django-admin.py

$ django-admin.py startproject mysite

See Also: django-admin.py help
          django-admin.py help --commands
          django-admin.py help <command> 

(p2)/opt/python/django/tutorial/mysite $ls
db.sqlite3  manage.py  mysite 

$ ls mysite
settings.py  urls.py  wsgi.py  ...

The manage.py is a thin wrapper on top of django-admin.py -- makes it easy
to run django.

In simplest form, url(regex, func), invokes function on regex url match.

Signature:

patterns is a module function which returns a list. e.g []
patterns(prefix (e.g. 'myapp.views'), url-config1, url-config2, ...) 
             which returns List of RegexUrlPattern or RegexURLResolver ;

     RegexURLResolver(regex, urlconf_module, kwargs, app_name=app_name, namespace=namespace)     
     RegexURLPattern(regex, callback, default_args=None, name=None):       

url() returns RegexUrlResolver or RegexURLPattern; 
patterns() ultimately reduces them to list of RegexURLPattern.
url(regex, view, kwargs=None, name=None, prefix='') 
       where view =   (urlconf_module, app_name, namespace) | func | include('appname.urls') | urlconf_module (e.g. app.urls)
include('appname.urls') converts the string to imported module.

ViewClassName.as_view() just returns a dispatch function which invokes get() etc class methods.

restframework View class should have permission_classes defined (must) and have get(), post(), etc methods defined :

class MyView(APIView):
    permission_classes = (IsAuthenticated,)

    @staticmethod
    def post(self, request, format=None):

Why would you use ModelAdmin class ? Ans: To reorder fields or create fieldsets or limit the fields or to create related objects (whose foriegnkey points to this) :

class QuestionAdmin(admin.ModelAdmin):
    fields = ['pub_date', 'question_text']
    # OR ...
    fieldsets = [
            (None,               {'fields': ['question_text']}),
            ('Date information', {'fields': ['pub_date']}),
        ]
    # inlines = [ChoiceInline] 

admin.site.register(Question, QuestionAdmin)

How do you receive component URL parameters ? e.g. /polls/32/ ? :

url(r'^(?P<question_id>\d+)/$', views.detail, name='detail'), ...
def detail(request, question_id):
   ....

How do you pass the model to template and how do you render ? :

def index(request):
    latest_question_list = Question.objects.order_by('-pub_date')[:5]
    context = {'latest_question_list': latest_question_list}
    return render(request, 'polls/index.html', context)

#  polls/templates/polls/index.html

{% if latest_question_list %}
<ul>
{% for question in latest_question_list %}
    <li><a href="/polls/{{ question.id }}/">{{ question.question_text }}</a></li>
{% endfor %}
</ul>
{% else %}
    <p>No polls are available.</p>
{% endif %}

Use pycscope -i filelist.txt and :cs add /tmp/cscope.out from vim; cs find f for file or module. g for definition.

What is django generic views used for ? :

- To view given model details using template (generic.DetailView)
- To view list of objects returned by Queryset using template (generic.ListView)
- To render given template. (TemplateView.as_view(template_name="about.html"))
- Provides ability to customize the view using keyword args:
      class MyView(django.views.generic.View):
              maxcount = 1000
      MyView.as_view(maxcount=500)
- Tie given model to the view so that functions like  self.get_object() works using
  pk value provided in URL conf keyword.   e.g.: url(r'^author/(?P<pk>\d+)/interest/$', ...)
- 

Where is my raw JSON body string that has been Posted ? It is available as string using request.body of handler. The request.data is the Python object.

What is the use of viewset in restframework ?

What are some builtin Django db objects manipulation functions ?

• node = DocumentNode.objects.from_hash(version_slug=qp['version'],...) # Create object from keyname args.
• DocumentComment.objects.filter(node=node)
• DocumentComment.objects.filter(pk=10)
• project = Project.objects.get(slug=request.data['project']) # You can also lookup by other keys
• node.update_hash(new_hash, commit) # Update object using given hash. Optionally commit (True) immediately.
• Sprint.objects.order_by('end')

How to handle query parameters ?

Good example from https://github.com/rtfd/readthedocs.org/blob/master/readthedocs/comments/views.py :

class CommentViewSet(ModelViewSet):

   serializer_class = DocumentCommentSerializer
   permission_classes = [CommentModeratorOrReadOnly, permissions.IsAuthenticatedOrReadOnly]

   def get_queryset(self):
       qp = self.request.QUERY_PARAMS
       if qp.get('node'):
           try:
               node = DocumentNode.objects.from_hash(version_slug=qp['version'], page=qp['document_page'], ...)
               queryset = DocumentComment.objects.filter(node=node)

           except KeyError:
               raise ParseError('To get comments by node, you must also provide page, version, and project.')
           except DocumentNode.DoesNotExist:
               queryset = DocumentComment.objects.none()
       elif qp.get('project'):
           queryset = DocumentComment.objects.filter(node__project__slug=qp['project'])

       else:
           queryset = DocumentComment.objects.all()
       return queryset

If you have SQL, but you want to create models from them, use:

$ python manage.py inspectdb > models.py

In essense:

• Change your models (in models.py).
• Run python manage.py makemigrations appname to create migrations for those changes
• Run python manage.py migrate to apply those changes to the database.

See Also:

https://docs.djangoproject.com/en/1.7/topics/migrations/
https://realpython.com/blog/python/django-migrations-a-primer/
https://docs.djangoproject.com/en/1.7/howto/initial-data/

See https://docs.djangoproject.com/en/1.6/ref/models/relations/ to find how to access related objects.

See http://www.slideshare.net/road76/scaling-django

See https://github.com/disqus/django-db-utils

django-debug-toolbar :

$ pip install django-debug-toolbar # settings.py 
INSTALLED_APPS = ( debug_toolbar, ) 
MIDDLEWARE_CLASSES = ( debug_toolbar.middleware.DebugToolbarMiddleware, ) 
INTERNAL_IPS = (127.0.0.1,)

save() is not thread safe. Use update()

django-sentry log viewer.

For asynchronity, use celery protocol (client library) with RabbitMQ as message broker. Other message brokers are also supported.

Use apache2-mpm-worker (not prefork) for better scaling with mod_wsgi in daemon mode. (not embedded mode)

SQLAlchemy is ORM alternative to builtin Django ORM.

pip install djangorestframework==3.1.0 Gives you web browsable API. Add this to: your INSTALLED_APPS = ( ... 'rest_framework',)

Follow http://www.django-rest-framework.org/ steps.

See http://ngenworks.com/blog/how-django-rest-framework-changed-my-life/

Use https://github.com/marcgibbons/django-rest-swagger for auto doc generation:

pip install django-rest-swagger
INSTALLED_APPS = ( ...  'rest_framework_swagger', .. ) ; 
patterns = ('', ...  url(r'^docs/', include('rest_framework_swagger.urls')),)

Use 'DEFAULT_AUTHENTICATION_CLASSES': ( 'rest_framework.authentication.BasicAuthentication', )

Viewsets by default support list, create, retrieve, update, partial_update, destroy methods.

See http://stackoverflow.com/questions/18969798/adding-more-views-to-a-router-or-viewset-django-rest-framework

Viewsets support @link and @action annotation in 1.* versions; Django 2.4+ support @detail_route and @list_route