如何在cakephp中为可选的关联模型创建包含字段的表单

I have the following models:

Posts->hasMany('texts');
Texts has a field 'body' that is required (not null)
Posts->hasMany('images);
Images has a field 'imagelink' that is required (not null)

When a user wants to create a post I want a single form to also add at least one text, or at least one image, or both.

My understanding is that because the formhelper uses the validator in TextsTable.php and ImagesTable.php it marks both the images.0.imagelink and the texts.0.body fields as required. And they are required if you actually want to create an entity of either type texts or images. But I want the creation of these associated entities optional. A user should be able to make a post with only an image for example.

How do I tell cakephp or the formhelper that not every post needs to have a text and an image? Is there something to add to the association definitions, or the validator of PostsTable.php?

I can create a post without any associated models just fine if I have a form with only the fields that are directly in the posts model, but not when I have one form for both the post and fields for associated models. Then the formhelper forces me to create an entity of all possible associated models that have a field in the form every time an entity of the base model is created.

In the end I also want to create as many texts and images as the user wants, but I think that's a different problem.

This is the relevant form in the ctp-file:

<?= $this->Form->create($post) ?>
<fieldset>
        <?php
            echo $this->Form->control('post_title');
            echo $this->Form->control('texts.0.body');
            echo $this->Form->control('images.0.imagelink');
        ?>
</fieldset>
<?= $this->Form->button(__('Submit')) ?>
<?= $this->Form->end() ?>

TextsTable.php (ImagesTable.php is basically the same)

    public function validationDefault(Validator $validator)
    {
        $validator
            ->integer('id')
            ->allowEmptyString('id', null, 'create');

        $validator
            ->scalar('body')
            ->requirePresence('body', 'create')
            ->notEmptyString('body');

        return $validator;
    }

Scenarios:

1. User writes something into texts.0.body and something into images.0.imageLink -> system creates a post, an associated text and an associated image.
2. User only fills in either texts.0.body or images.0.imagelink -> formhelper's client-side validation prevents sending the form but I want to only create the associated model for which the user filled out the form field.

I tried making two fields but then if a user wants to make a post with both an image and a text, the image and text aren't in the same post.