$fullModel = Model::find(1) // Get model with id 1
$idArray = $fullModel->only('id') // array containing id
// this does not work. You'll get back an empty collection
// It is trying to pull the id column off the collection object,
// not the models it contains
$models = Model::all()
$ids = $models->only('id')
// this will give you a collection of ids
$models = Model::all()
$ids = $models->pluck('id')
Laravel Eloquent only()