Configure a rails app for multiple databases

Hello Rails community

I cannot seem to find via Google what I had hoped would be
a simple issue

On a single DB system (currently, postgres 8.1.4),
I have two databases, each containing multiple tables.

I would like to configure my app and database.yml to recognize
these two databases.

What is the corrrect config for the database.yml ?
Is it something like:

adapter: postgresql
database: database1, database2


Is there some trick involved with this kind of configuration ?

Presumably, I would have open two db connections within
the app, as a result of which, dereferencing the db off of
these would uniquely identify the respective database and its
tables. But of course, I hope it would be ActiveRecord keeping
track of these distinctions.
But then, maybe this is not so, and it is necessary to fully qualify
the accesses to elements of the tables.

Anyhow, could someone please point me to info and examples
of this nature of access ?

Of course, doing this kind of thing in ruby itself is simple - I’ve
done this for simultaneous access to MySql and postgres, as in
when I transfered tables from the one to the other.

Maurice Y.

Here’s a good link

Maurice -

Each of your models use the database connection defined in database.yml
unless otherwise specified. If you’re using two databases, make one
your primary and stick its information in database.yml. For all your
models which use THE OTHER database(s) you need to tell each of them to
use a different connection.

Check out:
in the section where it says “Connection to multiple databases in
different models”

You’ll need to plug the following into each model.rb file that uses the
secondary database(s):

:adapter => “mysql”,
:host => “localhost”,
:username => “myuser”,
:password => “mypass”,
:database => “somedatabase”


You’ll need to plug the following into each model.rb file that uses the
secondary database(s):

:adapter => “mysql”,
:host => “localhost”,
:username => “myuser”,
:password => “mypass”,
:database => “somedatabase”

You can make it a bit simpler… in database.yml put:

adapter: mysql
database: somedatabase
username: myuser
password: mypass
host: localhost

And then in your model put:

establish_connection “other_db”

In fact if you have a group of models that will use that table and
are logically connected (say all parts of a blog system or whatever) you
could do:

class BlogSystem < ActiveRecord::Base
establish_connection “other_db”

class Blog < BlogSystem

class BlogPost < BlogSystem


You don’t have to get all complicated and establish another connection
if it’s on the same server.
The way I’ve been doing it - I just have…3 models that are in a
separate database.

set_table_name ‘otherdb.tablename’

That’s all I have to do. It’s not really DRY, but you’re going to have
to specify which database to connect to in each model that doesn’t use
the default DB anyway. Anyone has a better way, I’d like to hear it.

Very nice. Very clean. Very DRY.

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