Cakephp - Finding records with no associated records - cakephp

Question

Ok, so I have this:
$user_id = AuthComponent::user('id');
$joins = [
['table' => 'subscriptions',
'alias' => 'Subscription',
'type' => 'INNER',
'conditions' => [
'Subscription.thread_id = Thread.id',
'Subscription.user_id = '.$user_id
]
]
];
$unsubscribed = $this->Thread->find('all',[
'contain' => [
'Subscription' => ['conditions' => ['Subscription.user_id' => $user_id]]
],
'joins' => $joins,
'fields' => ['name','modified'],
'limit' => 10
]);
debug($unsubscribed);
It basically finds all threads with a subscription attached to the current user.
What I really want though, is the negative result. Or in other words: all the threads that do not have a subscription by the current user?
Is there a way to make the conditions negative? Or something like that?

Answer 1

Assuming your relations are:
Thread hasMany Subscription
Subscription belongsTo Thread
Your SQL would be:
SELECT Thread.*
FROM threads AS Thread
LEFT JOIN subscriptions AS Subscription
ON Thread.id = Subscription.thread_id
AND Subscription.user_id = ##user_id##
WHERE Subscription.user_id IS NULL;
The key concept is that you need a LEFT JOIN, not an INNER JOIN. This SQL joins all threads to all of the user's subscriptions AND does not eliminate those thread rows which do not have a subscription (i.e., the purpose of the LEFT JOIN). Then only select records that don't have a subscription (as found in the WHERE clause)
Translating to Cakephp:
$user_id = AuthComponent::user('id');
$joins = [
['table' => 'subscriptions',
'alias' => 'Subscription',
'type' => 'LEFT',
'conditions' => [
'Subscription.thread_id = Thread.id',
'Subscription.user_id = '.$user_id
]
]
];
$unsubscribed = $this->Thread->find('all',[
'conditions' => ['Subscription.user_id' => null],
'joins' => $joins,
'fields' => ['name','modified'],
'limit' => 10
]);
debug($unsubscribed);