Building custom web administrators for geographic data driven websites with Django

Marc Compte

University of Girona (SIGTE)

Django

Talks @ GeoPython

by Paolo Melchiorre

in Room 2
on 23rd april @ 11:45

Maps with Django

by Megan Luisa White

in Room 1
on 23rd april @ 21:00

Cal ToxTrack

GeoDjango

Use case

Django

Django makes it easier to build better Web apps more quickly and with less code.e.

Django is a high-level Python Web framework that encourages rapid development and clean, pragmatic design. Built by experienced developers, it takes care of much of the hassle of Web development, so you can focus on writing your app without needing to reinvent the wheel. It’s free and open source.

What is it?

Django

Why Django?

Django

Features (some)

MVC paradigm
HTML Templates (jinja2 like)
Integrated web server
i18n and l10n ready
Caching & Logging

URL management (routing)
CLI custom commands
Backup&restore
Admin!!
Object-Relational Mapping!!

+ Loads of third-party modules

Django Admin

What is it?

It’s not just scaffolding – it’s the whole house.e.

It’s the backend templates, the views, forms, controllers and even some models out-of-the-box without typing a single line.

Django Admin

0 lines of code

$ pip install django
$ django-admin startproject demo
$ django-admin startapp app
$ python manage.py migrate
$ python manage.py createsuperuser
$ python manage.py runserver

Django Admin

0 lines of code

Django Admin

0 lines of code

Django Admin

Adding new models (tables)

Django Admin

Adding new models (tables)

$ python manage.py makemigrations

$ python manage.py migrate

Django Admin

Adding new models (tables)

Django Admin

Adding new models (tables)

Django Admin

Tune up with one-liners

Django Admin

Tune up with one-liners

Django Admin

Tune up with one-liners

Django Admin

Tune up with one-liners

Django Admin

Tune up with one-liners

Django Admin

Other tune-ups: inlines

Django Admin

Adding geometries

GeoDjango

django-geojson + django-leaflet

Spatial databases

Non-spatial databases

Django Admin

Adding geometries

	GeoDjango	GeoJSON+Leaflet
Database	Spatial	Non-spatial
Field	Geometry	JSON
Spatial operations	Included	Requires modules
ORM integration	Yes	No
Spatial indexing	Yes	No

Django Admin

Adding geometries as JSON fields

(env)$ pip install django-geojson jsonfields django-leaflet

Add geom field to model

Django Admin

Adding geometries as JSON fields

Add leaflet map widget to the ModelAdmin

Django Admin

Creating geometries from the admin

Django Admin

Legacy databases

(env)$ python manage.py inspectdb > app/models.py

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': 'my_db_name',
        'USER': 'my_user',
        'PASSWORD': 'my_password',
        'HOST': 'my_server',
        'PORT': '5432',
    }
}

settings.py

Django ORM

SQL is an English-like language

>>> from .models import ObjectA

>>> all_as = ObjectA.objects.all()

SELECT * FROM ObjectA;

>>> filtered = ObjectA.objects.filter(
...     a_string='Test'
... )

>>> filtered2 = ObjectA.objects.filter(
...     a_number__gte=10
... )

SELECT * FROM ObjectA WHERE ...;

Django ORM

>>> filtered = ObjectA.objects.filter(
...     objectb__field1='Test'
... )

SELECT ObjectA.* FROM ObjectA, ObjectB WHERE ObjectA.objectb = ObjectB.id AND ObjectB.field1 = 'Test';

Is SQL an English-like language?

Django ORM

>>> filtered = Publication.objects.select_related(
...     'country', 'country_state', 'city'
... ).values(
...     'id', 'title', 'country__country_name',
...     'countrystate__name', 'city__name'
... )

SELECT publication.id, publication.title, country.country_name, countrystate.name, city.name
FROM publication 
INNER JOIN country ON ( publication.country_id = country.id ) 
INNER JOIN countrystate ON ( publication.countrystate_id = countrystate.id ) 
INNER JOIN city ON ( publication.city_id = city.id );

This is not an Enligsh-like sentence any more

Django ORM

>>> filtered = Publication.objects.all()
>>> for item in filtered:
...     print(item.id, item.title, 
...           item.country.country_name, ...)

SELECT publication.id, publication.title, country.country_name, countrystate.name, city.name
FROM publication 
INNER JOIN country ON ( publication.country_id = country.id ) 
INNER JOIN countrystate ON ( publication.countrystate_id = countrystate.id ) 
INNER JOIN city ON ( publication.city_id = city.id );

Caveats

Django ORM

>>> filtered = ObjectA.objects.exclude(
...     a_string__contains='Test'
... )
>>> for item in filtered:
...     # do something
>>> filtered2 = filtered.filter(
...     a_number__gte=10, 
...     a_date__gte=date,

...     a_date__lte=another_date,
...     geom__intersects=geometry
... )

>>> for item in filtered2:
...     # do something

Reusing queries

Other benefits

Django ORM

Versatility

Why it is better

Security

Readability

Questions?

marc.compte@udg.edu

@marcompte