Django and architecture : how to share a "referencial" database between projects?

Question

I come today with a design/architecture question concerning Django.

I work on several websites (hosted on the same server) which individually need geographical data (states, towns, etc.). Each project contains apps, and each app may contain models with ForeignKey fields to Town or State.

In order to not repeat myself, I wan't to build a database to store these towns and states, and to use it through Django projects.

Django provides a straightforwards way to use several databases in the same project, declaring it in the settings.py file and writing routers classes to hold reading and writing stuff. But that way, impossible to use select_related statement like :

job = get_object_or_404(Jobs.objects.select_related('state__town'), user=user)

This behaviour is just natural to me (impossible to make joins between databases, from scratch)...

My questions :

• Is it a good idea to consider introducing dblinks (I don't think so...) and can Django handle it (I didn't find any docs for this part) ?
• How would you proceed, facing this situation ?

A quick and dirty solution would be to import all geo data (towns, states...) in each project database, but it's not DRY at all :( :

python manage.py loaddata geo.json

Another solution may be to build a separated "geo" app, which could "serve" (I don't know how) the data to other projects... Actually, I tried GeoDjango, but it seems to be really complex, and it probably won't answer my question !

Thank you very much in advance for your answers !

Answer 1

Depending upon how static this data is, the simplest way might be to just define these towns and states in Python once and then import this definition in all of your separate projects:

# locations.py
STATES = (('S1', 'State 1'), ('S2', 'State 2'))
TOWNS = (('T1', 'Town 1'), ('T2', 'Town 2'))

And then you can, instead of using a Foreign key use a charfield specifying the options kwarg:

# app/models.py
from django.db import models
import locations # its on the path somewhere!

class MyModel(models.Model):
    state = models.CharField(max_length=5, options=STATES)
    town = models.CharField(max_length=5, options=TOWNS)

This approach is not very easy to update, and it does not record the relationship between towns and states (i.e. A town is in one state), however it is dead simple.

Answer 2

You can create a database view to bring in the static data from the other database. Then your model can point to this database view. You can even create joins within the database view.