association_exists model plugin for Sequel. Like association_join, allows you to filter dataset with association.

association_exists.rb

module Sequel
  module Plugins
    module AssociationExists
      
      module DatasetMethods
        
        def association_exists(association, &block)
          _association_exists(association, &block)
        end
        
        def association_not_exists(association, &block)
          _association_exists(association, negate: true, &block)
        end
        
        private
        
        def _association_exists(association, negate: false, &block)
          ar = model.association_reflections[association]
          parent_table_keys = Array(ar.send(:filter_by_associations_conditions_associated_keys))
          association_table_keys = Array(ar.send(:filter_by_associations_conditions_key))
          
          subquery = ar.associated_dataset
          subquery = subquery.where(association_table_keys.zip(parent_table_keys))
          subquery = subquery.instance_exec(subquery, &block) if block_given?
          
          where(negate ? ~subquery.exists : subquery.exists)
        end  
        
      end
      
      module ClassMethods
        Plugins.def_dataset_methods(self, DatasetMethods.public_instance_methods)
      end
      
    end
  end
end