Create an object with an exact number of sub-objects of the same type

Hi FLOW developers!

In my new flow project I have a simple problem, but can’t solve it until now.
My goal is to create an object “product” which allways has three “features”.
The object “feature” holds several properties which describes the details
of the feature.

The Flow entities are:

class Product {

     * @var \Doctrine\Common\Collections\Collection<\my\projects\Domain\Model\Feature>
     * @ORM\OneToMany(mappedBy="product")
    protected $features;

    public function __construct() {
        $this->features = new \Doctrine\Common\Collections\ArrayCollection();
        // allways three features!
        for ( $i = 0; $i < 3; $i++ ) {
            $instance = new \my\projects\Domain\Model\feature();
            switch ( $i ) {
                case 0: { $feature->setFeatureType(Feature::TYPE_AEI_FX); break; }
                case 1: { $feature->setFeatureType(Feature::TYPE_AEI_FY); break; }
                case 2: { $feature->setFeatureType(Feature::TYPE_AEI_FZ); break; }
            } // switch $i
            $this->features[] = $feature;
    } // public function __construct


class Feature {

    const  TYPE_AEI_FX         = 'Poduct Feature X';
    const  TYPE_AEI_FY         = 'Poduct Feature Y';
    const  TYPE_AEI_FZ         = 'Poduct Feature Z';

     * @var \my\projects\Domain\Model\Product
    * @ORM\ManyToOne(inversedBy="Features")
       * @Flow\Validate(type="NotEmpty")
    protected $product;



The problem: I have to create the product and its three features whitin one form.
I have one “Template” “Product/New.html” with partial “Product/FormFields.html” and
one partial “Feature/FormData.html”. (Feature/FormData has an <f:for each=“features”)
The form renders as expected.
When the user submits a new “product” one get an validation error like:

    Object of type "my\projects\Domain\Model\Product" with identity "8527b2fd-8a25-4344-bbe9-be06a5798a02" not found.This property is required. 

The error message is imho consistent because the product is not persisted at the moment.

I’ve found a (german) description for an analogous problem, but they
have an existing “mother” as I understand.[snippet]=74&tx_in2snippets_pi1[action]=detail&tx_in2snippets_pi1[controller]=Snippet&cHash=20bf6bed1ab88b5bd571fa8cc5aefd6b

Has someone a hint if this problem is solvable?
And of course: how?