Caching in CakePHP based on a per-record expiry date - cakephp

Question

I've run into a bit of a dilemma with Cake 2.4's caching system and I was wondering if anyone can think of a simply solution.
I have made a function within a component which I use for connecting to an API to obtain data. I also want to to cache data in order to make it more efficient.
The problem is that exactly when the cache expires depends on a field in the $result array (from the API) called $result['expiry']. So, I've done this:
class ApiComponent extends Component {
public function getRecords($data) {
$cacheName = $data['Model'] . "_" . $data['action'];
// IMPOSSIBLE because we don't have $result:
// Cache::set(array('duration' => '+' . $result['expiry'] . ' days'));
$result = Cache::read($cacheName);
if (!$result) {
$result = $this->connect('getRecords',$data);
Cache::set(array('duration' => '+' . $result['expiry'] . ' days'));
Cache::write($cacheName, $result);
}
return $result;
}
public function connect($endpoint,$data) {
// Code for connecting to the API
}
}
The problem is that, for some reason, Cake needs me to specify the expiry for a write AND a read, despite the expiry timestamp being present in the cache file itself.
I've commended the necessary line as IMPOSSIBLE in my example above. According to the book, this is how it's supposed to work. Unfortunately it doesn't make much sense to me.
I understand having to set the expiry before a write but why do I need to set the expiry before a read when the cache file itself has a UNIX timestamp specifying exactly when the cache expires, based on what I did when I set the write.
Please note that accessing the API is only costing me 100ms so there wouldn't be any point saving the expiry to the database and accessing that every time unless I also cached the local database output but that seems like a truly bizzare thing to have to do: caching a cache expiry!

Answer 1

Theoretically you don't necessarily need the duration when reading from the cache. The reason for having it available on read, is to be able to invalidate the cache in case the duration changed ever since the data was cached.
https://github.com/cakephp/cakephp/commit/caa7bb621871706baf664b5e2e4f562353f3671f
Unfortunately there is no clean way of overcoming this auto-magic as a duration option value will be used no matter what, when not defining a custom one, the one from the default configuration will be used, and if that one is lower than the one used on write, then your cache is going to be invalidated prematurely.
A (kinda ugly) workaround would be to set an extraordinary high duration dummy value for the read operation, you're losing the auto-magic, but your cache is not going to be invalidated prematurely:
Cache::set(array('duration' => '+10 years'));
$result = Cache::read($cacheName);