use MyApp::MySQLSchema ;
use MyApp::OracleSchema ;

our $schema_mysql = MyApp::MySQLSchema->connect( sub { # code that returns a DBI handle  } ) ;
our $schema_oracle = MyApp::OracleSchema->connect( sub { # code that returns another DBI handle  } ) ;

my $company = $schema_mysql->resultset('Company')->find($company_id) ; # get 1 row/object
my $widget = $company->find_related('widgets', $widget_id) ; # get 1 related row/object
my $parts = $widget->search_related('widget_parts', { in_stock => 1 }) ; # get all matching related rows/object
my $r = $widget->create_related('widget_part', { # create a row
  comments => $comments,
  creation_time => time(),
}) ;
$schema_mysql->txn_do( sub {
  $r->insert() ;
  $r->update() ;
}) ;