Symfony and Sonata get Class with "pcode"

I'm having problem to get the Class which is called by the 'Add New' and the Modal Window.

The situation is that, I have a 'Add New' button on my entry with sonata_type_model:

->add('rfid', 'sonata_type_model', array(
                'class' => 'Admin\IdManageBundle\Entity\RFID',
                'property' => 'barcode'
            ))

when I click on 'Add New' it shows me a Modal Window, with which I can create new RFID.

but my RFID class has a barcode object that must be filled with the data of the class had the 'Add New' button!

I can handle the parent class with

->add('barcode', 'text', array(
                'data' => $this->getRequest()->get('pcode')
            ))

but I want to be able to get the Entity Manager of the responded 'pcode'
In my case $this->getRequest()->get('pcode') returns:

admin_product_accessory_audio_audio.admin.audio

and it's not readable by $this->getConfigurationPool()->getContainer()->get('doctrine')->getRepository($this->getRequest()->get('pcode'))

It has made me crazy!! :D

thanks in advance