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5. Modifying form fields dynamically depending on edited object

It is a quite common situation when you need to modify your form’s fields because of edited object’s properties or structure. Let us assume you only want to display an admin form field for new objects and you do not want it to be shown for those objects that have already been saved to the database and now are being edited.

This is a way for you to accomplish this.

In your Admin class’ configureFormFields method you are able to get the current object by calling $this->getSubject(). The value returned will be your linked model. Then, you should be able to dynamically add needed fields to the form:

use Sonata\AdminBundle\Admin\Admin;
use Sonata\AdminBundle\Form\FormMapper;

class MyModelAdmin extends Admin
// ...

  protected function configureFormFields(FormMapper $formMapper)
    // Description field will always be added to the form:
    $formMapper->add('description', 'textarea');

    $subject = $this->getSubject();

    if ($subject->isNew()) {
        // The thumbnail field will only be added when the edited item is created
        $formMapper->add('thumbnail', 'file');

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