Limitations

The current implementation of Cycle ORM includes multiple limitations.

#Filter by relations from external databases

It is currently not possible to automatically filter the selection based on values of related entities located in an external source. You must manually filter the selected result after loading all the data. Though, it is possible to use fetchData of Cycle\ORM\Select to avoid entity instantiation before the filtering.

Since you can provide any iterable source to the Cycle\ORM\Iterator you can create nested generator:

use Cycle\ORM;

function filterByExternal(ORM\Select $select, $value) {
    foreach($select->load('external')->fetchData() as $item) {
        if ($line['external']['value'] == $item) {
            yield $item;
        }
    }
}

// ...

foreach (new ORM\Iterator($orm, User::class, filterByExternal($select, $value)) as $user) {
    print_r($user);
}

The given approach will minimize the amount of allocated memory.

You can also use the load option of $select->load to pre-filter data.

#MyISAM

It is not reliable to use Cycle with MySQL MyISAM engine as it does not support transactions, which can guarantee the recovery from persisting errors. Use the InnoDB engine instead.

#Cascade = false

Please note that turning cascade option off completely disables relation store sequence. This makes uni-directional relations useless for persisting, only use this option if the relation is considered "read-only".