About validations that require many-to-many models to be stored in intermediate tables

For example, for many-to-many models of User and Group, there is an intermediate table User_Group.

When creating a group, how do I validate that user_group keeps at least one record, i.e., it must be linked to the user?

in group.rb validate:user_ids,presence:true
I think there is a way to describe as a candidate, but is there any other way?