How in Symfony2 to make friends a select without multiple with an Entity property that is ManyToMany?

Question

symfony

Hello.
There is an entity called Brief, it can belong to several categories, i.e. it has a $categories property annotated with ManyToMany and JoinTable .
However, depending on the role of the user, he can choose either only one category, or several, which means select multiple and simple select.
I tried to do with the entity field type without multiple - it displays select, but does not save, since Entity expects an ArrayCollection (ManyToMany).
How to be? Maybe there are some options?

Answer 1

for a limited user, use a field without multiple, and then after submitting the form, but before saving, turn it into an ArrayCollection - create a collection directly in the same field and add your one category to it.