Fetching Existing Users In Users Field Doesnt Work When entries.saveEntry Event Triggerred From Frontend

Question

As the title says, I can successfully return the "existing user IDs" from an entry field if the "entries.saveEntry" event is called after saving the entry from the CMS admin area; however, if I save an entry via a front-end form, the same code produces empty results.

I've used xDebug to verify that the objects are the same line by line; somehow the data isn't there for $users->ids() for front-end triggered events.

// get entry
$entry = craft()->entries->getEntryById($entryId); // elementType => "Entry"

// get ALL users related to entry
$users = craft()->elements->getCriteria(ElementType::User); // elementType => Craft\UserElementType
$users->status = null;
$users->relatedTo = [$entry]; // elementType => "Entry"
$userIds = $users->ids(); // elementType => Craft\UserElementType

Example result when triggered from backend (good):

array(
    0 => 251,
    1 => 252,
    3 => 257
)

Example result when triggered from front-end (help!):

array()

Answer 1

Turns out I was inadvertently "emptying" my user field on form post. Essentially I had named one of the form fields "fields[customUserField]" which upon submitting the form, was saving an empty value into the "Users" field. Then my custom event would trigger and fetch the "Users" field thereby retrieving an empty "array".

So nothing is wrong with the code below:

// get entry
$entry = craft()->entries->getEntryById($entryId);

// get ALL users related to entry
$users = craft()->elements->getCriteria(ElementType::User);
$users->status = null;
$users->relatedTo = [$entry];
$userIds = $users->ids();