many to many relation in database schema and oop class diagram

I have Student and Group entities. Student can have many groups and Group can have many students too. so in database I should have middle class and change manytomany relation to oneTomany and ManyToone.

my question is how should I design class diagram in oop? if middle table does not have any extra field(just student_id and group_id) then I think no middle class is need in oop, is this true or not?