postgres_ext.rb

require 'arel/nodes/binary'
module Arel
  module Nodes

    class ContainedInHStore < Arel::Nodes::Binary
      def operator; :"<@" end
    end

    class ContainedInArray < Arel::Nodes::Binary
      def operator; :"<@" end
    end

  end
end

require 'arel/visitors/postgresql'
module Arel
  module Visitors
    class PostgreSQL
      private

      def visit_Arel_Nodes_ContainedInHStore o, collector
        infix_value o, collector, " <@ "
      end

      def visit_Arel_Nodes_ContainedInArray o, collector
        infix_value o, collector, " <@ "
      end

    end
  end
end

require 'arel/predications'

module Arel
  module Predications

    def contained_in_array(other)
      Nodes::ContainedInArray.new self, Nodes.build_quoted(other, self)
    end

  end
end

module ActiveRecord
  module QueryMethods
    class WhereChain

      def contained_in_array(opts, *rest)
        build_where_chain(opts, rest) do |rel|
          case rel
          when Arel::Nodes::In, Arel::Nodes::Equality
            column = left_column(rel) || column_from_association(rel)
            equality_for_hstore(rel) if column.type == :hstore

            if column.type == :hstore
              Arel::Nodes::ContainedInHStore.new(rel.left, rel.right)
            elsif column.respond_to?(:array) && column.array
              Arel::Nodes::ContainedInArray.new(rel.left, rel.right)
            else
              Arel::Nodes::ContainsINet.new(rel.left, rel.right)
            end
          else
            raise ArgumentError, "Invalid argument for .where.overlap(), got #{rel.class}"
          end
        end
      end

    end
  end
end