# Help! Rails database connection guru needed!

**URL:** <https://www.ruby-forum.com/t/help-rails-database-connection-guru-needed/52756>\
**Category:** Engines\
**Created:** [January 18, 2006, 6:33pm UTC](https://www.ruby-forum.com/t/help-rails-database-connection-guru-needed/52756 "2006-01-18T18:33:44Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![sayoyo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ba8739/32.png) [@sayoyo](https://www.ruby-forum.com/u/sayoyo)\
**Post date:** [January 18, 2006, 6:33pm UTC](https://www.ruby-forum.com/t/help-rails-database-connection-guru-needed/52756/1 "2006-01-18T18:33:44Z")

</div>

Hi,

I really need help to understand what is happening  
while Rails connect to a database,(we area actually  
using postgresql, so my example will be with  
postgresql) What I understand is Rails is able to  
connect to different DB. Actually, this is what we  
want,and we have made some tests, everything is juste  
fine. However, all these tests lead us to some  
important questions that we did find the answer from  
the documentation, So we hope the communauty can help  
us to answer those questions!!!

Question A- How rails disconnect the connection?  
As we can see in the source code :

Call stack for postgresql

1- any controller  
2- connectionspecification.establish\_connection  
3- ActiveRecord::base.postgresql\_connection(config)  
4- ConnectionAdapters::PostgreSQLAdapter.new(  
PGconn.connect(), logger )  
5- connection\_specification.establish\_connection  
@@defined\_connections[self] = spec

The connection is made while Rails calls  
PGconn.connect(), then the connection  
stored in @connection of the adapter class. while a  
request is send to the adapter,  
the adapter will sends the request to the database via  
its variable @connection.  
But where exactly the disconnection is done while we  
connect ourself to another  
database??? As we can see in the source code  
“remove\_connection”

connectionspecification  
def self.remove\_connection(klass=self)  
conn = @@defined\_connections[klass]  
@@defined\_connections.delete(klass)  
active\_connections[klass] = nil  
conn.config if conn  
end

bascially, it removes the “table-linked-class” from  
the class variable @@defined\_connection and  
@@active\_connections. Actually it does not do anything  
to disconnect the actually connection, So we wonder  
will it lead to a memory leak of the ruby-rails and  
the connected database??? Is there anything we miss  
that make us misunderstand the mecanism of connection  
and reconnection???

Question B  
inside the same methode of a controller, like:  
[www.myrails.com/mycontroller/mymethode1](http://www.myrails.com/mycontroller/mymethode1). It is  
possible  
to change the database, because the example give on  
the  
[Peak Obsession](http://wiki.rubyonrails.com/rails/pages/HowtoUseMultipleDatabases)  
the basic idea is to change the connection, while user  
change methode(link to a new page or something…) is  
it possible  
to change the database inside the same method? like

class mycontroller \< ApplicationController

def mymethode1  
# first connection  
ActiveRecord::base.establish\_connection(:adapter =\>  
“postgresql”,  
:host =\> “1.2.3.4”,  
:database =\> “db1”,  
:username =\> “user”,  
:password =\> “pwd”)

```
# do something here !!!!!

# second connection to anther database
ActiveRecord::base.establish_connection(:adapter =>

```

“postgresql”,  
:host =\> “1.2.3.5”,  
:database =\> “db2”,  
:username =\> “user”,  
:password =\> “pwd”)

```
# do something here agains !!!!!

# third connection to another database
ActiveRecord::base.establish_connection(:adapter =>

```

“postgresql”,  
:host =\> “1.2.3.6”,  
:database =\> “db3”,  
:username =\> “user”,  
:password =\> “pwd”)

```
# do something here agains !!!!!
    # then done

```

end

Can we do this??? If we have connection to three  
different databases, what Rails don exactly??? Does it  
have three connections inside somewhere or It  
disconnect the old one each time we make a new  
connection??? or there is other mecanism??? And how  
does it manange all this connection???

Thanks you very much and amy help will be very  
appreciated!!!

Saiho

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