CakePHP2.3: Building complex conditional Model->find() options - mysql

Question

I'm not savvy with MySQL or databases generally, so here's a model of my data (table{cols}]) in order to make my question coherent:
Domains{id, name} Note: 'domains' here does not refer to web domains
Subdomains{id, domain_id, name}
Items{id, subdomain_id, name}
SubdomainsItems{id, subdomain_id, item_id} no domain_id column!
My Items Controller has a function, fetchWithin($domains, $subdomains) which, ultimately, should just execute one of two complexish find(). It's the complexish I can't get past.
Programmatically I can achieve this, but I'm quite certain the better way is by clever joins and the like. Alas, currently this is approach:
If $domainsis empty, do only steps 2&3, otherwise:
foreach($domains as $d): get all the rows of Subdomains where Subdomain.domain_id = Domains.id as $subdomains
foreach($subdomains as $s) : go get all the rows of SubdomainsItems where SubdomainsItems.subdomain_id = Subdomains.id as $item_ids
foreach($items_ids as $i): get all the rows of Items where Items.id = SubdomainsItems.items_id
This works, but I think this is obviating the power of a relational database and I'd like to understand how this should be done (ie. according to either Cakephp convention or simply by whatever MySQL statement would achieve this).
Help would be hugely appreciated, I try to learn the more complex aspects of SQL but it just goes right over my head. :S

Answer 1

Understanding the necessary query
With the structure described in the question the kind of query necessary is of the form:
SELECT
*
FROM
items
LEFT JOIN
subdomains ON (
items.subdomain_id = subdomains.id
)
LEFT JOIN
domains ON (
subdomains.domain_id = domains.id
)
WHERE
domains.name = "foo"
AND
subdomains.name IN ('some', 'list', 'of', 'subdomains');
Compared to the logic in the question this joins all three tables together and permits finding all items by domain name, or subdomain name (or any other criteria involving any or all three tables); Generally speaking if you want to find data in a db and use more than one query to get it - there's a more efficient way to do it.
Implementing the find call
There are a number of ways of creating such a query with Cake. The simplest, probably, is to use the join key and just specify the joins explicitly:
function fetchWithin($domains = null, $subdomains = null) {
$params = array(
'joins' => array(
array('table' => 'subdomains',
'alias' => 'Subdomain',
'type' => 'LEFT',
'conditions' => array(
'Subdomain.id = Item.subdomain_id',
)
),
array('table' => 'domains',
'alias' => 'Domain',
'type' => 'LEFT',
'conditions' => array(
'Domain.id = Subdomain.domain_id',
)
)
)
);
if ($domains) { // single value or an array
$params['conditions']['Domain.name'] = $domains;
}
if ($subdomains) { // single value or an array
$params['conditions']['Subdomain.name'] = $subdomains;
}
return $this->find('all', $params);
}