Polymorphic #where method in ActiveRecord

activity.rb

class Activity < ActiveRecord::Base
  belongs_to :actor, polymorphic: true
  belongs_to :thing, polymorphic: true
  belongs_to :target, polymorphic: true

  def self.polywhere(opts)
    t = arel_table
    ands = opts.map do |assoc, obj|
      left_eq = t["#{assoc}_id"].eq(obj.id)
      right_eq = t["#{assoc}_type"].eq(obj.class.model_name)
      and_node = Arel::Nodes::And.new([left_eq, right_eq])
      Arel::Nodes::Grouping.new(and_node)
    end
    ors = ands.reduce do |memo, and_node|
      if memo
        Arel::Nodes::Or.new(and_node, memo)
      else
        and_node
      end
    end
    where(ors)
  end
end

gistfile1.rb

p = Property.first
Activity.polywhere(actor: p, thing: p, target: p)

to_sql.sql

SELECT "activities".* FROM "activities" WHERE (("activities"."actor_id" = 1 AND "activities"."actor_type" = 'Property') OR ("activities"."target_id" = 1 AND "activities"."target_type" = 'Property') OR ("activities"."thing_id" = 1 AND "activities"."thing_type" = 'Property'))