KeyVal on Google Datastore

google_key_val.rb

require 'google/cloud/datastore'

module Ruba
  # This use the Google Datastore as a key value storage.
  # One could argue that Memcache would be more appropriate.
  # usage:
  # 
  ## class DoSomething
  ##   include GoogleKeyVal
  ##
  ##   # this will be used as the "namespace" of the keys, leave blank
  ##   # to use the name of the current class.
  ##   def self.service_id
  ##     'DoSomething'
  ##   end
  ##
  ##   def process
  ##     results = get_gkey(:results)
  ##     if results
  ##       results[:total] += 1
  ##     else
  ##       results = {
  ##         total: 0,
  ##         start: Time.now.utc.to_s
  ##       }
  ##     end
  ##
  ##     store_gkey(:results, results)
  ##   end
  ##
  ##   def cleanup
  ##     del_gkey(:results)
  ##   end
  ## end

  module GoogleKeyVal
    def store_gkey(key, value)
      gkey = Google::Cloud::Datastore::Key.new "GoogleKeyVal", namespaced_key(key)

      entity                 = Google::Cloud::Datastore::Entity.new
      entity.key             = gkey
      entity["value"]        = value.to_json
      entity["namespace"]    = self.class.key_namespace
      entity.exclude_from_indexes! "value", true

      Ruba.logger.debug "Storing key #{gkey.name} with #{value.to_json}"

      self.class._google_datastore.save entity
    end

    def get_gkey(key)
      gkey = Google::Cloud::Datastore::Key.new "GoogleKeyVal", namespaced_key(key)
      entities = self.class._google_datastore.lookup gkey

      Ruba.logger.debug "Getting key #{gkey.name} with #{entities.first}"

      if entities.any?
        value = entities.first.properties.to_hash['value']
        JSON.parse(value).deep_symbolize_keys if value
      end
    end

    def del_gkey(key)
      gkey = Google::Cloud::Datastore::Key.new "GoogleKeyVal", namespaced_key(key)
      self.class._google_datastore.delete gkey
    end

    def namespaced_key(key)
      "#{self.class.key_namespace}:#{key}"
    end

    module ClassMethods
      def _google_datastore
        @@datastore ||= Google::Cloud::Datastore.new
      end

      def key_namespace
        try(:service_id) || self.name
      end
    end

    def self.included(base)
      base.extend(ClassMethods)
    end
  end
end