gistfile1.php

// in User entity:
    public function addRole(Role $roles) {
        $this->roles[] = $roles;
        return $this;
    }

    public function removeRole(Role $roles) {
        $this->roles->removeElement($roles);
    }

    public function getRoles() {
        return $this->roles->toArray();
    }

    public function addFormRole(Role $roles) {
        $this->roles[] = $roles;
        return $this;
    }

    public function removeFormRole(Role $roles) {
        $this->roles->removeElement($roles);
    }

    public function getFormRoles() {
        return $this->roles;
    }


// in UserType:
        $builder->add('formRoles', 'entity', array(
            'class' => 'Acme\DemoBundle\Entity\Role',
            'property' => 'name',
            'multiple' => 'true',
            'expanded' => 'true'
        ));

// in template:
        <div class="control-group">
            {{ form_label(form.formRoles, 'Roles', {'label_attr': {'class': 'control-label'}}) }}
            <div class="controls">
                {{ form_errors(form.formRoles) }}
                {{ form_widget(form.formRoles, {'attr': {'class': 'none'}}) }}
            </div>
        </div>