Einführung in Django

Was ist Django und wofür braucht man das?

made by Arne Schauf @asmaps

26.10.2014 - NetHack 2014

Attention please!

Vortrag unter:

http://asmaps.github.io/django-presentation/

Übersicht

Was ist Django?
Komponenten
Datenbank
Tools
Praxiseinsatz
Alternativen
Where to start?

Was ist Django?

Django Reinhardt

* 23.1.1910✝ 16.5.1953

The Web framework for perfectionists with deadlines. Django makes it easier to build better Web apps more quickly and with less code.

High-level Webdevelopment Framework
Python 2 & 3
DRY
BSD Lizenz
Version 1.7.1

MVT

Model, View, Template(, Controller)

Der Weg eines Requests

urls.py


from django.conf.urls import patterns, include, url

from django.contrib import admin
admin.autodiscover()

urlpatterns = patterns(
    '',
    url(r'^allauth/', include('allauth.urls')),
    url(r'^accounts/', include('accounts.urls')),
    url(r'^admin/', include(admin.site.urls)),
    url(r'^', include('main.urls')),
)

main/urls.py


from django.conf.urls import patterns, url
from django.views.generic import TemplateView
from main.views import (
    HomeView, HelpView, AboutView, ...)
...

urlpatterns = patterns(
    '',
    url(r'^$', HomeView.as_view(), name="home"),
    url(r'^about/$', AboutView.as_view(), name="about"),
    url(r'^legal/$',
        TemplateView.as_view(template_name='main/legal.html'),
        name="legal"),
    url(r'^help/$', HelpView.as_view(), name="help"),
    ...
)

Views

Function based views (FBV)


# urls.py

url(r'^evaluate/(?P<id>\d+)/$', 'main.views.evaluate'),


# views.py

@login_required
def evaluate(request, id):
    return render_to_response(
        'evaluate/evaluate.html',
        {
            'questionnaire' : Questionnaire.objects.get(id=id),
            'active'        : 'evaluate',
        },
        context_instance=RequestContext(request)
    )

Class based views (CBV)

komfortabler als FBV
Standard-Funktionalität wiederverwendbar
Vererbung
Generic Views
Tip: ccbv.co.uk

Beispiel TemplateView


# urls.py

url(r'^about/$', AboutView.as_view(), name="about"),


# views.py

from django.views.generic import TemplateView

class AboutView(TemplateView):
    template_name = "main/about.html"

Beispiel DetailView


# urls.py

url(r'^(?P<slug>[a-zA-Z0-9_\-]+)/$',
    HostDetailView.as_view(), name="info"),


# views.py

from django.views.generic import DetailView

class HostDetailView(DetailView):
    model = Host
    template_name = 'host/detail.html'

ORM & Models

Python to DB Mapping
Model = Tabelle
Datenvalidierung
Anlegen/Ändern/Löschen von Datensätzen
Kein "Raw-SQL"
Datenbank unabhängig
Vererbung

Model Beispiel


# models.py

from django.db import models

class Host(models.Model):
    subdomain = models.CharField(max_length=256, validators=[
        RegexValidator(
            regex=r'^(([a-z0-9][a-z0-9\-]*[a-z0-9])|[a-z0-9])$',
            message='Invalid subdomain: only a-z, 0-9 and - are allowed'
        ),
        domain_blacklist_validator])
    domain = models.ForeignKey(Domain)
    update_secret = models.CharField(max_length=256)
    comment = models.CharField(
        max_length=256, default='', blank=True, null=True)

Model Vererbung Beispiel


# models.py

from django.db import models

class BaseModel(models.Model):
    modified = models.DateTimeField(auto_now=True)
    created = models.DateTimeField(auto_now_add=True)

    class Meta:
        abstract = True

class Comment(BaseModel):
    comment = models.TextField()

class Value(BaseModel):
    value = models.IntegerField()

Forms & Validierung

Automatische Generierung von HTML <form>
"POST-Data to Python"
Datenvalidierung
Sicherheitsmechanismen

Form Beispiel


# forms.py

from django import forms

class BeginEndForm(forms.Form):
    begin = forms.DateField()
    end = forms.DateField()


# views.py

from django.views.generic import FormView

class CalcDayDifferenceView(FormView):
    form_class = BeginEndForm

    def form_valid(self, form):
        diff = form.cleaned_data['end'] - form.cleaned_data['begin']
        # do sth with the difference
        ...

Form Beispiel Template


{# calc_day_difference.html #}
...

    {% csrf_token %}
    {{ form }}
    

....

ModelForms

Forms aus Models generieren
Eingegebene Daten wieder in die DB speichern
Neue Datensätze erstellen

Model Form Beispiel


# models.py

from django.db import models

class Thing(models.Model):
    related_thing = models.ForeignKey('Thing', null=True, blank=True)
    name = models.CharField(max_length=255,
                            help_text='The name of the thing')


# views.py

from django.views.generic import CreateView
from .models import Thing

class CreateThingView(CreateView):
    model = Thing

Model Form Template


# thing_form.html

Create Thing

    
        {% csrf_token %}
        {{ form.as_table }}

Das Ergebnis

Admin Interface

Generiertes Web-Datenbank-Frontend
Anlegen, bearbeiten und löschen
Praktisch kein zusätzlicher Code

Admin Interface - Code


# admin.py

from django.contrib import admin
from things.models import Thing

admin.site.register(Thing)

Admin Interface - Login

Admin Interface - Übersicht

Admin Interface - Add Thing

Admin Interface - Things

Migrations

Automatisiertes anlegen der DB
Verfolgen von Änderungen an den Models/am Schema
kein Code oder SQL
Bis 1.7 nur über Third-Party-App "south"
Seit 1.7 in Django

asmaps:~/example_project > python manage.py makemigrations things
Migrations for 'things':
  0001_initial.py:
    - Create model Thing

asmaps:~/example_project > python manage.py migrate
Operations to perform:
  Apply all migrations: admin, things, contenttypes, auth, sessions
Running migrations:
  Applying contenttypes.0001_initial... OK
  Applying auth.0001_initial... OK
  Applying admin.0001_initial... OK
  Applying sessions.0001_initial... OK
  Applying things.0001_initial... OK