update a field-collection from a computed field - drupal-7

Question

I'm able to retrieve the fields of the field collection attached to my content type, using codes like :
foreach ($entity->field_collection[LANGUAGE_NONE] as $line) {..}
or from an entity wrapper.
But I'm definitely unable to update the collection fields with values computed in the computed field, like I usually do with other CCK fields, like :
$entity->field_regular[LANGUAGE_NONE][0]['value'] = $value ;
then it is saved normally, as if I edited field_regular 'by hand'.
with collection this won't work (does nothing visible) :
$entity->field_collection[LANGUAGE_NONE][$key]['field_coll_field0'][LANGUAGE_NONE][0]['value'] = $value ;
// entity wrapper way
$coll = entity_load('field_collection_item', array($line['entity']->item_id));
$wcoll = entity_metadata_wrapper('field_collection_item', $coll[$key);
$wcoll->field_coll_field0->set($value) ;
any save() methods gives me a blank page (infinite cgi loop) :
entity_save('field_collection_item',$coll);
wcoll->save();
what should I know to programmatically save collection fields ?
thanks, Jerome

Answer 1

Please check Entity metadata wrappers doc page with simple example how to update a field collection, for example:
<?php
// Populate the fields.
$ewrapper = entity_metadata_wrapper('node', $node);
$ewrapper->field_lead_contact_name->set($contact_name);
$ewrapper->field_lead_contact_phone->set($contact_phone);
$ewrapper->field_lead_contact_email->set($contact_email);
// Create the collection entity and set it's "host".
$collection = entity_create('field_collection_item', array('field_name' => 'field_facilities_requested'));
$collection->setHostEntity('node', $node);
// Now define the collection parameters.
$cwrapper = entity_metadata_wrapper('field_collection_item', $collection);
$cwrapper->field_facility->set(intval($offset));
$cwrapper->save();
// Save.
$ewrapper->save();
?>
So probably you need to do as below:
try {
// Entity wrapper way.
$coll = entity_load('field_collection_item', array($line['entity']->item_id));
$wcoll = entity_metadata_wrapper('field_collection_item', $coll);
$wcoll->field_coll_field0 = $value;
$wcoll->save();
} catch (Exception $e) {
drupal_set_message(t('Error message: #error.',
array('#error' => $e->getMessage())), 'error');
watchdog_exception('MYMODULE', $e);
}
Adding try/catch should prevent you from having a blank page. However if you've still an issue, check watchdog logs or any errors in PHP log file.