$rs = $db->resultset('Poem')->search({
    'user.name'     => 'tobyink',
    'comments.text' => { '!=' => 'bad' },   # DBIx handles this NOT
    'country.name'  => \'!= country_2.name' # literal SQL for this NOT
}, {
    prefetch => {
        artwork => [
            { artist   => 'country' },
            { comments => { user => 'country' } },
        ],                          # table aliased here to 'country_2'
    },
});