correct usage of "min" within validating a symfony choice form

Question

As described under the book http://symfony.com/doc/current/reference/constraints/Choice.html#min I would like to use the "min" options to validate a choice with must have at least one selected checkbox in it

The form looks like

->add('usergroups', 'entity', array('class' => 'PrUserBundle:Group','property' => 'name','required' => true, 'multiple'  => true, 'expanded'  => true))

My validation.yml looks liek:

Pr\UserBundle\Entity\User:
constraints:
//...
properties:
    //.....
    locations:
        - Length:
            min: 7 { message: "Please select at least one group." }

I am totally wrong doing this, but the book won't tell me any more helpful so I ask you. OR do I have to use True/False?

Answer 1

You are trying to use the Length constraint rather than the choice.

You should be using it like..

Pr\UserBundle\Entity\User:
    constraints:
    //...
    properties:
        //.....
        locations:
            - Choice:
                min: 7
                minMessage: "Please select at least one group."

All of the options that are featured on that page would be in a single level array like

- Choice: { min: 7, minMessage: 'message' }

or

- Choice:
    min: 7
    minMessage: 'message'