Dynamic database selection based on URL in Django

Question

Let's say the first page of the app has two links. Is it possible to pick the database depending on which link is clicked? The databases both have the same models, but different data. For example, let's say the application contains students for different colleges A and B. If link for A is clicked, then database for A is used which contains the students for college A. The entire application after this point should use database for college A.

I understand there are ways to work around this problem by just designing the databases differently, i.e. having a college field, and just filtering out students with the particular college affiliation. But I am hoping to find a solution using Django to just use two different databases.

There is a page in django docs that describes having multiple databases — vishes_shell
– vishes_shell, Commented Sep 22, 2016 at 17:18
Nothing on that page seems helpful, .using('default') is not a realistic solution. Is there another way to pick databases dynamically? — Harvinder
– Harvinder, Commented Sep 22, 2016 at 17:24
Have you looked at db routers? Only need to figure out how to pass user selection into the router. — serg
– serg, Commented Sep 23, 2016 at 2:25

vishes_shell · Accepted Answer · 2016-09-22 17:27:20Z

1

So you need to store the chosen database in session or smth and you can easily pick the database. From the docs

>>> # This will run on the 'default' database.
>>> Author.objects.all()

>>> # So will this.
>>> Author.objects.using('default').all()

>>> # This will run on the 'other' database.
>>> Author.objects.using('other').all()

edited Sep 22, 2016 at 17:27

answered Sep 22, 2016 at 17:21

vishes_shell

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5 Comments

Harvinder Over a year ago

Yeah, this is something along the lines of what I'm looking for, but is there an alternative to .using('default')? So basically another way to pick the database dynamically?

vishes_shell Over a year ago

@Harvinder why this method doesn't satisfy you? I mean, if this is in the docs it certainly a good choice.

vishes_shell Over a year ago

@Harvinder you can also use SQLAlchemy, but that another story and not compatible with django-models.

Harvinder Over a year ago

This method requires significant change to the code. If I rewrote the project this is a good choice but I was hoping for something that requires less code changes.

vishes_shell Over a year ago

@Harvinder then you need to specify more precisely what is the code that you have, the way you are trying to achieve, because the .using() method is pretty neat.

A. J. Parr · Accepted Answer · 2017-05-24 03:52:53Z

You could mix together Database Routers with this GlobalRequestMiddleware solution to create a database router which inspects the request to figure out which database to use.

class RequestDatabaseRouter(object):
  def db_for_read(self, model, **hints):
    request = GlobalRequestMiddleware.get_current_request()
    key = self.get_database_key(request)  # Implement get_database_key
    return key

There may be some way to inject the request into **hints, which I think would be preferable over the Middleware solution, however, I'm unaware how to at the moment. You may need to make sure the GlobalRequestMiddleware is called after the AuthenticationMiddleware otherwise you may not have the user on the request to inspect.

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