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? Willkommen & kurze Übersicht

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

Created with Raphaël 2.1.0

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