How to use set() on a field within a field collection?

Question

I have a custom entity type, and I'm defining its form, which extends ContentEntityForm. During my save() function, I want the form to conditionally unset fields based on the values of other fields. (example: unset the value of a list select field if a certain checkbox is checked off)

I can't seem to accomplish this with $form_state->setValue() or $form_state->setValueForElement(), in both cases my code is seemingly ignored and the select widget is not unset upon finishing saving (although a var_dump of $form_state->getValues() at the end of the function shows that the values array is indeed being modified the way I want it to be).

However, the following code seems to work nicely for the title field (defined via baseFieldDefinitions(), is not inside a field collection):

$entity = $this->getEntity();
    $entity->set('title', array(array("value" => "aaaaaaaa")));
$entity->save();

My title for the newly saved entity does indeed show up as "aaaaaaaa"

Is it possible to target fields inside field collections in this way using this $entity object? Or is this the totally wrong approach?

Answer 1

It's not really clear to me why you don't change the values on the entity, but save() is too late.

The entity is built in buildEntity()/copyFormValuesToEntity(), if you want to change how it is build based on form_state values, you have to change them by overriding those methods and doing your changes first.