I'm using form to edit some data. 
one of the form field:

```
$builder ->add('cities', 'entity', array(
    'class'    => 'Vendor\SomeBundle\Entity\City',
    'multiple' => true
));

```

everthing works fine - i have some preselected cities in accordance with the database.

Now i want to limit choices to cities form specific country.
So I get collection of cities and set 'choices' option:

```
$builder ->add('cities', 'entity', array(
    'class'    => 'Vendor\SomeBundle\Entity\City',
    'multiple' => true,
    'choices'  => $citiesCollection
));

```

The choice list is limited but no cities are selected.

i try to set this preselected cities using 'data' option but this also does not work

```
$builder ->add('cities', 'entity', array(
    'class' => 'Vendor\SomeBundle\Entity\City',
    'multiple' => true,
    'choices'  => $citiesCollection
    'data'     => $citiesSelected
));

```

trying different approaches, passing ArrayCollection, array, array of keys but nothing works...
It is even possible?