I would like to know how to use queryBuilder expression within a **formBuilder**.

The general use of query builder in formBuilder is :

```
$builder->add('client', EntityType::class, array(
    'class'=>Entity::class,
    'query_builder'=>function(EntityRepository $er) {
        return $er->createQueryBuilder("e")
                  ->where("e.active=1");
    },
));

```

Now, I would like to use `->expr()->in()` within `where` statement.  

The problem is, unlike entity repository, `$er->expr` doesn't works.

What should I do to access `expr` within the `where` statement?