On Thu, Jan 28, 2010 at 10:41 AM, Chris Curvey <ccur...@gmail.com> wrote:
> Is there a way to use raw SQL with multiple databases? I thought it
> might be something like:
>
> from django.db import connection
> cursor = connection.cursor(using="mydb")
>
> but that complains about an unexpected keyword arg.
It is possible, but not like that.
There are a couple of ways to handle raw SQL over multiple databases,
depending on exactly what you want to do.
If you want to do a SELECT on a specific model, but with some
eccentric FROM/WHERE/HAVING clause that Django doesn't support, you
can use the new raw query method:
Author.objects.raw('SELECT id, name FROM library_authors WHERE ....')
To make this a query on a different database:
Author.objects.db_manager('mydb').raw('SELECT id, name FROM
library_authors WHERE ....')
The db_manager() clause gives you a version of the objects manager
that has been forced to use the 'mydb' database. Every manager
provides a raw() method that allows you to call raw sql, and return
model objects. So - this query will run your raw SQL on the mydb
database.
If you have a database router installed, you may not need the
db_manager() query. The raw() query will interrogate the master router
to find the appropriate read database; if your router is set up to
direct 'Author' read queries to 'mydb', the original
Author.objects.raw() query will operate on the mydb database
automagically.
If you want to do an UPDATE, INSERT, or some other SQL query, you need
to fall back to using a cursor as before. To access a multi-db cursor,
we haven't changed the connection interface - we've changed the way
you get a connection.
from django.db import connections
cursor = connections['mydb'].cursor()
cursor.execute('INSERT ....')
That is, the 'db.connection' object has been replaced with an index
called 'db.connections', keyed by database alias. Each of those
connections behaves as the single connection did in 1.1.
The old 'db.connection' object has been retained for backwards
compatibility, but it is assumed to be no more than an alias for:
connections['default']
I hope that clarifies things.
Yours,
Russ Magee %-)
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