Digest predicates

digest_queries.rb

module DigestQueries
  def predicate_builder
    @predicate_builder ||= super.tap do |pb|
      pb.register_handler(Digest::Instance, DigestHandler.new(pb))
    end
  end

  class DigestHandler
    def initialize(predicate_builder)
      @predicate_builder = predicate_builder
    end

    def call(attribute, value)
      type = case value
      when Digest::MD5; 'md5'
      when Digest::SHA1; 'sha1'
      when Digest::SHA2; "sha#{value.length * 8}"
      when Digest::SHA256; 'sha256'
      when Digest::SHA384; 'sha384'
      when Digest::SHA512; 'sha512'
      else
        raise ArgumentError, "Did not recognise #{value.inspect} as a Digest object"
      end

      binvalue = ActiveModel::Type::Binary::Data.new(value.digest)
      bind = predicate_builder.build_bind_attribute(attribute.name, binvalue)
      digest(attribute, type).eq(bind)
    end

    private
      attr_reader :predicate_builder

      def digest(attribute, type)
        Arel::Nodes::NamedFunction.new("digest", [attribute, Arel::Nodes::Quoted.new(type)])
      end
  end
end

ActiveRecord::Base.extend(DigestQueries)

text_digest = Digest::SHA256.new.update(text)
Model.where(text: text_digest)