For admin views that need to take advantage of searching and filtering, we've chosen to use Ransack.
Ransack is a Ruby gem that makes searching relatively painless. It has excellent documentation, but if you're looking for an example of how it's being used on Forem, we've implemented it to help searching and sorting user reports.
The view responsible for managing user reports can be found at
/admin/moderation/reports and Ransack can be seen in use on the index action of the
For Forem, Ransack is being used exclusively in admin, for search problems in other parts of the app we use PostgreSQL Full Text Search.