Gantry::Docs::DBConn(3)

Name
Gantry::Docs::DBConn - how database connection info flows through Gantry

Intro
One of the problems with separating models from the rest of any application is how to inform the model of the database connection information. This document explains how that information makes its way to the model.

This document does not apply to DBIx::Class, which has a cleaner way of moving this information from conf to code. See Gantry::Plugins::DBIxClassConn for how Gantry works with dbic.

Environments (a.k.a. Engines)
Gantry supports plugable engines. Currently there are engines for CGI and mod_perl versions 1.3, and 2.0. Further, many gantry apps have scripts which also want to use the models. There is now a comprehensive solution for all of these.

  Scripts
The simplest environment is the script. A script has essentially three choices for where to obtain connection information: (1) hard coded in the script, (2) taken from the command line, (3) taken from a config file (which could be an apache conf).

Where the information comes from matters not to the gantry. Once you know where your information will come from, you have two options for passing it to the model.

If the information is known at compile time (i.e. it is hard coded), you may simply say:

    use Gantry::Utils::DBConnHelper::Script {
        dbconn => 'dbi:Pg:dbname=some_db;host=127.0.0.1',
        dbuser => 'someone',
        dbpass => 'super_secret',
    };

Note that the dbconn key must have the full dsn needed by the DBI's connect method. This is true for all environments.

If you must calculate the information do the above in two steps:

    use Gantry::Utils::DBConnHelper::Script;

    # pull in your information from command line or conf file

    Gantry::Utils::DBConnHelper::Script->set_db_conn_info(
        {
            dbconn => $dsn,
            dbuser => $dbuser,
            dbpass => $dbpass,
        }
    );

Note that in both cases you should pass a hash reference.

If you need to access models which inherit from Gantry::Utils::AuthCDBI (or one of its authentications cousins), you need to also call set_auth_db_conn_info on Gantry::Utils::DBConnHelper::Script. That call is the same as the one for set_db_conn_info, except that the hash keys are auth_dbconn, auth_dbuser, and auth_dbpass.

  mod_perl
Gantry is ready to help you with connection information. The normal approach is to use PerlSetVars in your httpd.conf:

    <Location />
        PerlSetVar dbconn dbi:Pg:dbname=some_db;host=127.0.0.1
        PerlSetVar dbuser someone
        PerlSetVar dbpass super_secret

        PerlSetVar auth_dbconn dbi:Pg:dbname=auth_db;host=127.0.0.1
        PerlSetVar auth_dbuser auth_user
        PerlSetVar auth_dbpass double_super_secret
    </Location>

  CGI
Note that gantry does user authentication, but only in the mod_perl environment at present. Even so, some of your models may inherit from an auth utils module. In that case, you need to provide the auth values below.

Gantry also helps CGI scripts. Simply include the dbconn, dbuser, and dbpass keys (and their auth counterparts, if needed) in the config section of the hash you pass to Gantry::Engine::CGI->new:

    my $cgi = Gantry::Engine::CGI->new( {
        locations => {
            '/' => 'App::Base',
            # ...
        },
        config => {
            # ...
            dbconn => 'dbi:Pg:dbname=some_db;host=127.0.0.1',
            dbuser => 'someone',
            dbpass => 'super_secret',
        }

Internals
So, how does the data flow? Of course, it depends slightly on the environment. Each has its own source of data and therefore its own scheme. But they all conform to a single API described here.

Let's start at the other end. When any gantry model wants to use a database, it calls db_Main. That method is responsible for returning a working dbh. Here is the db_Main from Gantry::Utils::CDBI (the others look strikingly similar):

    sub db_Main {
        my $dbh;

        my $helper = Gantry::Utils::DBConnHelper->get_subclass();

        $dbh       = $helper->get_dbh();

        if ( not $dbh ) {
            my $conn_info = $helper->get_conn_info();

            $db_options->{AutoCommit} = 0;

            $dbh = DBI->connect_cached(
                    $conn_info->{ 'dbconn' },
                    $conn_info->{ 'dbuser' },
                    $conn_info->{ 'dbpass' },
                    $db_options
                    );
            $helper->set_dbh( $dbh );
        }

        return $dbh;

    } # end db_Main

So, there is a base class Gantry::Utils::DBConnHelper which can return the subclass which assists the current model. That subclass responds to get_dbh with a cached handle if one is available (or undef if not). If the handle is true, it is returned directly. Otherwise, the if block asks the helper for the connection info as a hash reference. Then it uses that to connect to the database. Finally, it gives the helper subclass the newly minted connection handle for caching.

This completely separates the concerns of the modules. The model knows how to connect to a database, but relies completely on the helper to know what database connection info to supply AND for caching of connections, enabling each environment to cache in the most resonable way.

  Gantry::Util::DBConnHelper
The base class for all helpers is Gantry::Util::DBConnHelper. It is mostly a documentation module. It does have an import method so scripts with hard coded connection info can save a statement. Further, it has two class accessors: get_subclass and set_subclass. The former is called by the model, so it will know which class is actually providing the connection info for and caching of handles. The later is called by the subclasses of Gantry::Util::DBConnHelper.

  Subclasses of Gantry::Util::DBConnHelper
The easiest way to understand the subclasses of the connection helper is to see an example. The simplest example is the script helper. I'll show just the regular connection routines (since auth works the same with 'auth_' in front of 'db' in all variable names and hash keys).

    package Gantry::Utils::DBConnHelper::Script;
    use strict; use warnings;

    use base 'Gantry::Utils::DBConnHelper';

    Gantry::Utils::DBConnHelper->set_subclass(
        'Gantry::Utils::DBConnHelper::Script'
    );

    my $dbh;
    my $conn_info;

    sub get_dbh {
        return $dbh;
    }

    sub set_dbh {
        my $class = shift;
        $dbh      = shift;
    }

    sub get_conn_info {
        return $conn_info;
    }

    sub set_conn_info {
        my $class  = shift;
        $conn_info = shift;
    }

    1;

At the top of the script we see that the module's full name is Gantry::Utils::DBConnHelper::Script and that it inherits from Gantry::Utils::DBConnHelper.

The first thing it should do is register with the base class. There can only be one connection helper in a given environment, so it calls the class method set_subclass with its own name. Now the base module will tell db_Main that this is the subclass with the info and cache.

The remainder of the script implements the simplest possible scheme for storing connection information and cached database handles.

Remember that scripts call set_conn_info directly (Gantry::Engine::CGI does this in its constructor) or supply the info in a hash reference parameter to use. The other methods are called by db_Main as needed.

The other helpers work similarly with two differences. Obviously, they use different caching schemes (mod_perl helpers use pnotes). But, set_conn_info is also handled differently. Here's where they are:

    engine type   where set_conn_info is called
    -----------------------------------------------------------
    scripts       manually before database work begins
    CGI           Gantry::Engine::CGI->new
    mod_perl      not called, params are fished from dir_config
                  on every request

So, the Gantry::Utils::DBConnHelper subclasses for mod_perl engines fish their connection information directly from the set vars in their get_conn_info methods.

Auth Differences
If you use any model class which inherits from a module with Auth in the name, you need to supply the auth_* parameters in PerlSetVars (for mod_perl), as config hash keys (for CGI), or in a call to set_auth_conn_info (for self standing scripts).

Author
Phil Crow <philcrow2000@yahoo.com

Copyright and License
Copyright (c) 2006, Phil Crow.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.6 or, at your option, any later version of Perl 5 you may have available.