Detecting and Examining Databases 101

Arthur Axel fREW Schmidt

YAPC::NA

Orlando, Florida

2014 June 23, 16:00

(blah blah hiring blah)

Me

What's the problem?

sometimes you need to generate different SQL per DB
sometimes you need to just treat $dbh's differently

Why not $dbh->{Driver}->{Name}

Driver != Database
important (to me) example: ODBC

People do try this, way too often

What works?

Nested "re"detection
DBIC does this...but it's
- incomprehensible
- not extensible
- not reusable
- almost completely hardcoded

Solution: DBIx::Introspector

Faithful reimplementation of the DBIC algorithm
Complete initial configuration fits in 50LoC
Can add to or modify that configuration for just yourself

DBII in action

Details: new

DBIx::Introspector->new(drivers => '2013-12.01')

Details: decorate_driver_(un)connected

$dbii->decorate_driver_unconnected(
   Pg => 'concat_sql' => '? || ?',
)

$dbii->decorate_driver_connected(
   Pg => 'rdbms_version' => sub {
      my $dbh = shift;

      $dbh->selectcol_arrayref('SELECT VERSION()')->[0]
   },
)

Details: get

$dbii->get($dbh, $dsn, 'concat_sql')

my $dbh;
$dbii->get(sub { $dbh }, $dsn, 'concat_sql', {
   dbh_fallback_connect => sub {
      $dbh = DBI->connect(...)
   },
});

Links:

Slides: https://frioux.github.io/dbix-introspector-presentation/
Announcement

Details: Driver

name
parents
connected_options
unconnected_options
connected_determination_strategy
unconnected_determination_strategy

Details: Driver (DBI)

DBIx::Introspector::Driver->new({
   name => 'DBI',
   connected_determination_strategy => sub { $_[1]->{Driver}{Name} },
   unconnected_determination_strategy => sub {
      my $dsn = $_[1] || $ENV{DBI_DSN} || '';
      my ($driver) = $dsn =~ /dbi:([^:]+):/i;
      $driver ||= $ENV{DBI_DRIVER};
      return $driver
   },
})

Details: Driver (Mongo {made up example})

DBIx::Introspector::Driver->new({
   name => 'Mongo',
   parents => ['DBI'],
})

Details: add_driver

$dbii->add_driver({
   name => 'Mongo',
   parents => ['DBI'],
})

Details: replace_driver

$dbii->replace_driver({
   name => 'DBI',
   connected_determination_strategy => sub {
      $_[1]->{Driver}{Name}
         ? $_[1]->{Driver}{Name}
         : $_[1]->{Driver}{MegaDrive}
   },
   unconnected_determination_strategy => sub {
      my $dsn = $_[1] || $ENV{DBI_DSN} || '';
      my ($driver) = $dsn =~ /dbi:([^:]+):/i;
      $driver ||= $ENV{DBI_DRIVER};
      return $driver
   },
})