Can I use custom data in chained API calls?

[DaveFF]

I'm trying to do the following, to get events of certain types, and (if any) a Host participant that matches a contact in a contact reference custom field on the event:

Code: [Select]

// Get all event mobilisations, and the host participant that matches the school if any
$eventGetResult = civicrm_api('Event', 'get', array(
  'version'       => 3,
  'sequential'    => 1,
  'event_type_id' => array('IN' => $mobEventTypeIds),
  'api.Participant.get' => array(
    // 'event_id' => '$value.id' is implicit
    'participant_role_id' => PARTICIPANT_ROLE_ID_HOST,
    'contact_id'          => '$value.custom_104_id',
  ),
));
if (civicrm_error($eventGetResult)) {
  print_r($eventGetResult);
  die('Error getting events');
}

But I'm getting "Error in call to Participant_get : participant_contact_id is not a valid integer". I have checked that output makes sense (and the Event output includes the custom_104_id) if I don't include the contact_id line. So, in general can custom fields returned by an outer call be matched on by an inner call in a chained API?

[totten]

My recollection of chaining is a bit rusty, but I think that chaining relies heavily on support from the underlying API calls. In this snippet, it seems like the outer call to "Event.get" would need to return a field called "custom_104_id" for use by the chained call.

The notation "custom_123" is supported by the "Contact" API, but I don't think it's supported by Event API (or most other APIs). For other entities, one has to call CustomValue API. It might be possible to do a 3-step chain (Event.get => CustomValue.get => Contact.get), but I don't know anyone's tried that before.