Categories field is losing its value when programmatically updating other fields’ values

Question

I have a webhook that fetches an entry, modifies one of its custom Text field values and then saves the entry. However there is also a required Categories field on the entry, and when I do this, I get a validation error because the Categories field is blank.

Here’s the relevant code:

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

$entry->setContentFromPost(array(
    'myTextField' => $newValue
));

// Let's see if it saves.
// Field validation should happen automatically
if (craft()->entries->saveEntry($entry))
{
    Craft::log('Entry updated (ID: '.$entry->id.').');
}
else
{
    Craft::log('Could not updated the entry (ID: '.$entry->id.').', LogLevel::Error);
}

How do I save the entry without losing its existing Categories field value?

Answer 1

Update - Craft 3

This has been fixed. The relational field will retain its original value when an entry is re-saved.

You no longer need to apply a workaround to get the expected behavior.

---

Original - Craft 2

This is, admittedly, super awkward right now. To prevent a relational field from losing its value when saving an entry, you have to explicitly set its value to null:

$entry->setContentFromPost(array(
    'myCategoriesField' => null
    // ...
));

However, this only works for relational fields that aren’t set to Required. If the field is set to Required, you have to just re-set the field to the same element IDs that were already selected:

$entry->setContentFromPost(array(
    'myCategoriesField' => $entry->myCategoriesField->ids()
    // ...
));

(FWIW, this will stop being awkward in Craft 3, as we done some major refactoring under the hood to fix issues like this.)

Answer 2

I'm probably missing something here, but can't you just query for the entry model and only modify the field you want to change?

$criteria = craft()->elements->getCriteria(ElementType::Entry);
$criteria->id = 1;
$entries = $criteria->first();

if ($entry)
{
    $entry->setContentFromPost(array(
        'fieldToChange' => 'newValue'
    ));

    // Validate the entry model here if necessary

    craft()->entries->saveEntry($entry);
}