[Catalyst] One App, multiple databases

Tomas Doran bobtfish at bobtfish.net
Fri Nov 21 00:03:37 GMT 2008

On 20 Nov 2008, at 14:51, Jose Luis Martinez wrote:

> Jonathan Rockway escribió:
>> * On Wed, Nov 19 2008, Jose Luis Martinez wrote:
>>>     my ($self, $c) = @_;
>>>     my $user_db = $c->lookup_the_users_db();
>>>     $self->{'dsn'} =~ s/#DATABASE#/$user_db/;
>>>     return $self;
>>> }
>> I am really surprised that this works at all.  When do you  
>> actually ever
>> connect to the database with the DSN in $self->{dsn}?  (I am also
>> surprised that the DBIC version works.)
> It looks like the models don't connect to the database until it is  
> first needed, so changing the properties with which they connect  
> lets me get away with it. I think the fact that I'm working with  
> app_server.pl -f helps me start each request without preestablished  
> db connection.
>> Anyway, mutating objects is wrong.  You should do things like this:
>>   package MyApp::Model::UsersDatabase;
>>   ...
>>       my ($self, $c) = @_;
>>       return $c->user->get_database($c->config->database_info);
>>   }
>> <snip>
>> The idea is that each user has his own database connection, stored in
>> the user object, and Catalyst just returns the right thing when  
>> you say
>> $c->model('UsersDatabase').  This is much easier to reason about.
> But I'll still have to change Model::DBI and/or Model::DBIC::Schema  
> connection information on the fly... how should I do this in a  
> clean way?

No, you don't.

In your application code, instead of saying $c->model('DB')->dbh,  
with the example above, you would say $c->model('UsersDatabase'), and  
that would return you the dbh which the user object had generated.

You then work with it in exactly the same way as if you were using  

This means that you have to re-implement the connection logic of  
Catalst::Model::DBI in your user class. The only tricky bit is the  
stay_connected function, which is 16 lines long.

I don't think the code police will break down your door if you pinch  
this function verbatim. ;)


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