Creating collection of read-only entities in Symfony2 - forms

Question

My question is about creating collection of entities. I know about "How To Embed Collection Forms" and successfully used it. But in this case I have:
Simple class
class Thing
{
/**
* #ORM\ManyToMany(targetEntity="DicStyle", mappedBy="things")
* ....
*/
protected $styles;
public function __construct()
{
$this->styles = new ArrayCollection();
}
}
Dictionary of styles
class DicStyle
{
.....
}
I don't need to create form for DicStyle objects, because this is read only objects = dictionary (unchangeable). So, I want to create a form with something like this:
$builder->add('styles', 'collection', array(
'type' => 'entity', 'options' => array(
'class' => 'MyEntityBundle:DicStyle'
)
))
Of course it's pseudo-code. I can not imagine how to implement it.
The result
Suppose, I have:
Table "Thing" with one row (id = 1).
Table "DicStyle" with 6 rows (id = from 1 to 6).
Table "mtm_thing_dicstyle" (many-to-many table)
In the form, I choose two DicStyle (id=3, id=5) for the Thing. So, the mtm_thing_dicstyle contains:
thing_id dicstyle_id
-------- ------------
1 3
1 5

Answer 1

Try this form:
$builder->add('styles', 'entity', array(
'class' => 'MyEntityBundle:DicStyle'
'property'=>'name' //what property do you want to see when you select,
'multiple" => true //you'll be able to select many DicStyle
'expanded' => false //it'll shown on a multiple choice select tag
)
);

Answer 2

To select one or more objects in a form to relate them to your result you can use the form field type "entity". (See form-types)
$builder->add('styles', 'entity', array(
'class' => 'MyEntityBundle:DicStyle',
'property' => 'name', // property you want to be displayed
'expanded' => true,
'multiple' => true
)
);
This would render checkboxes and therefore the possibility to select multiple entities to be referenced.
Keep in mind, if you use multiple => true there are two options:
expanded => false: renders a multiselect field
expanded => true: renders checkboxes
See form-entity-type-options