Right now gem can interact with attributes and relations only via :if block. It seems to be a really easy change to support :unless conditional as Rails does in validate method.
Inspired by this Issue.

Can be merged after this pr.
Would like to hear any feedback.

What is the current behavior?

has_many :actors, if: Proc.new { |record| record.actors.any? }

What is the new behavior?

has_many :actors, unless: Proc.new { |record| record.actors.empty? }

Checklist

Please make sure the following requirements are complete:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes /
  features)
• All automated checks pass (CI/CD)