# Configure a rails app for multiple databases

**URL:** <https://www.ruby-forum.com/t/configure-a-rails-app-for-multiple-databases/76359>\
**Category:** Rails\
**Created:** [November 17, 2006, 9:41pm UTC](https://www.ruby-forum.com/t/configure-a-rails-app-for-multiple-databases/76359 "2006-11-17T21:41:25Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Maurice\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/aeb1de/32.png) [@Maurice\_Y](https://www.ruby-forum.com/u/Maurice_Y)\
**Post date:** [November 17, 2006, 9:41pm UTC](https://www.ruby-forum.com/t/configure-a-rails-app-for-multiple-databases/76359/1 "2006-11-17T21:41:25Z")

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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:

> production:  
> adapter: postgresql  
> database: database1, database2  
> etc.

??

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.

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**Author:** ![Maurice\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/aeb1de/32.png) [@Maurice\_Y](https://www.ruby-forum.com/u/Maurice_Y)\
**Post date:** [November 17, 2006, 9:56pm UTC](https://www.ruby-forum.com/t/configure-a-rails-app-for-multiple-databases/76359/2 "2006-11-17T21:56:33Z")

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Here’s a good link

[http://wiki.rubyonrails.com/rails/pages/HowtoUseMultipleDatabases](http://wiki.rubyonrails.com/rails/pages/HowtoUseMultipleDatabases)

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<div class="post-metadata">

**Author:** ![Maurice\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/aeb1de/32.png) [@Maurice\_Y](https://www.ruby-forum.com/u/Maurice_Y)\
**Post date:** [November 17, 2006, 10:02pm UTC](https://www.ruby-forum.com/t/configure-a-rails-app-for-multiple-databases/76359/3 "2006-11-17T22:02:10Z")

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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: [Peak Obsession](http://rails.rubyonrails.com/classes/ActiveRecord/Base.html)  
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):

ActiveRecord::Base.establish\_connection(  
:adapter =\> “mysql”,  
:host =\> “localhost”,  
:username =\> “myuser”,  
:password =\> “mypass”,  
:database =\> “somedatabase”  
)

Marc

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<div class="post-metadata">

**Author:** ![Maurice\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/aeb1de/32.png) [@Maurice\_Y](https://www.ruby-forum.com/u/Maurice_Y)\
**Post date:** [November 17, 2006, 10:15pm UTC](https://www.ruby-forum.com/t/configure-a-rails-app-for-multiple-databases/76359/4 "2006-11-17T22:15:30Z")

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> You’ll need to plug the following into each model.rb file that uses the  
> secondary database(s):
> 
> ActiveRecord::Base.establish\_connection(  
> :adapter =\> “mysql”,  
> :host =\> “localhost”,  
> :username =\> “myuser”,  
> :password =\> “mypass”,  
> :database =\> “somedatabase”  
> )

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

other\_db:  
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_  
they  
are logically connected (say all parts of a blog system or whatever) you  
could do:

class BlogSystem \< ActiveRecord::Base  
establish\_connection “other\_db”  
end

class Blog \< BlogSystem  
end

class BlogPost \< BlogSystem  
end

etc…

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<div class="post-metadata">

**Author:** ![Maurice\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/aeb1de/32.png) [@Maurice\_Y](https://www.ruby-forum.com/u/Maurice_Y)\
**Post date:** [November 17, 2006, 10:15pm UTC](https://www.ruby-forum.com/t/configure-a-rails-app-for-multiple-databases/76359/5 "2006-11-17T22:15:31Z")

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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.

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<div class="post-metadata">

**Author:** ![Maurice\_Y](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/aeb1de/32.png) [@Maurice\_Y](https://www.ruby-forum.com/u/Maurice_Y)\
**Post date:** [November 17, 2006, 10:19pm UTC](https://www.ruby-forum.com/t/configure-a-rails-app-for-multiple-databases/76359/6 "2006-11-17T22:19:31Z")

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Very nice. Very clean. Very DRY.