Symfony Form过滤下拉选项

Question

I have for with drop down entity Customer by field name, my question how to change form for filter by name. Example in my drop down many customer, and I write "a" and in drop down remained only who have first letter in name "a"

        $builder
        ->add('customer', 'entity', array(
            'class' => Customer::class,
            'attr' => array('class' => 'form-control select2 all_customers'),
            'property' => 'name',
            'empty_value' => 'Choice Customer',
            'query_builder' => function ($repository) {
                /** @var CustomerRepository  $repository */
                return $repository->getAllQuery();
            },
            'required' => false
        ))

this my template what need to do which create text field for filter

{{ form_start(form) }}
{{ form_errors(form) }}

{{ form_label(form.customer, label|default(null), {'label_attr': {'class': 'control-label'}}) }}
{{ form_widget(form.customer, {'attr': {'class': 'select2', 'type': 'text'}}) }}

 {{ form_end(form) }}