DBIx::Class join, prefetch

Over the last 15 years I've joined two database tables into a one-to-many relationship about a billion times. But I've never had any software let me loop the left table and right tables separately before. Turns out this magic has been in DBIx::Class for several years.

Runnable demo.

When table 'foo' is in a one-to-many relationship with table 'bar', you can:

my $foo_rs = $schema->resultset('Foo')->search(
   {},
   {
      join     => 'bars',
      prefetch => 'bars',
      order_by => 'me.id',
   }
);

while (my $foo = $foo_rs->next) {
   printf "%s\n", $foo->id;
   if (my $bar_rs = $foo->bars) {
      while (my $bar = $bar_rs->next) {
         printf "   %s\n", $bar->desc;
      }
   }
}

Output:

1
2
   aaa
   bbb
   ccc
3

Still one SQL statement against the database (fast!). Much prettier than ugly manual de-duping of redundant columns.