many to many relation in a form view symfony 2

Question

I have a many to many relation between two entities.

I display then a form to add entityA to entityB. Isn't possible to add a customized form (I mean in the twig view) in order to enable the user sometimes to select one value and sometimes more than one?

when I want the user to select more than one value, I use this

<select multiple>
{% for entity in entitys %}
<option> 
{{entity.id}}

 </option>
{%endfor%}
</select>

otherwise this

 <select >
    {% for entity in entitys %}
    <option> 
    {{entity.id}}

     </option>
    {%endfor%}
    </select>

but now the problem is how to submit the form. the

<button  type="submit"  class="btn btn-info"    value="NEXT STEP " /> 

Here is the whole form

<form method="post">
  <select >
    {% for entity in entitys %}
    <option> 
    {{entity.id}}

     </option>
    {%endfor%}
    </select>

<input  type="submit"     /> 

</form>

no longer submit the form. any ideas plz??

here is my entire twig view

  <h2> STEP {{step}} </h2>
  <form method="post">
<select >
{% for entity in entitys %}
<option value="{{entity.id}}"> 
{{entity.id}}

 </option>
{%endfor%}
</select>

<input  type="submit"  class="btn btn-info"     /> 

</form>
  <br>
  <br>

Answer 1

In your formbuilder you can add some options like in my exemple:

The aim is to map your field to an entity (to setup the list). Don't forget to add a method _tostring to your mapped entity to make symfony able to represent your entity as a text in your select.

In your formType

public function buildForm(FormBuilder $builder, array $options) {
        $id = $this->id;

        $builder->add(
            'addressees',
            'entity',
            array(
                        'class' => 'Pref27\MailBundle\Entity\Addressee',
                        'property' => 'name',
                        'multiple' => true,
                    'expanded' => false,
                        'required' => true,
                        'label' => 'mail.add.theme';
                }
            )
        );
    }

In your formControler

$editForm = $this->createForm(new FormType(), $entity);
return array(
            'form'   => $editForm->createView()
        );

In your view

<form action="{{ path('theControllerActionWitchIsResponsibeOfRecordingIntoDatabase' }}" method="post" {{ form_enctype(edit_form) }}>
        {{ form_widget(edit_form) }}
        <p>
            <button type="submit">Next step</button>
        </p>
</form>

The type of field rendered will depend on setting of multiple and expended

select tag                                  expanded=false  multiple=false
select tag (with multiple attribute)        expanded=false  multiple=true
radio buttons                               expanded=true   multiple=false
checkboxes                                  expanded=true   multiple=true

you can find more information about entity type in form here : http://symfony.com/doc/2.0/reference/forms/types/entity.html

EDIT:

From your twig view form's action is missing try to add

<form method="post" action="{{ path("theRouteOfYourControllerWitchRecordTheData")}}">

don't forget to add {{form_rest(form) }} To tell twig to add the CSRF token

and don't forget to add value in your select's option

<select multiple>
  {% for entity in entitys %}
       <option value="{{entity.id}}">{{entity.name}}</option>
  {%endfor%}
</select>