query_results.rb

# Copyright 2014 Google Inc. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


require "delegate"

module Gcloud
  module Datastore
    class Dataset
      ##
      # QueryResults is a special case Array with additional values.
      # A QueryResults object is returned from Dataset#run and contains
      # the Entities from the query as well as the query's cursor and
      # more_results value.
      #
      # Please be cautious when treating the QueryResults as an Array.
      # Many common Array methods will return a new Array instance.
      #
      # @example
      #   require "gcloud"
      #
      #   gcloud = Gcloud.new
      #   datastore = gcloud.datastore
      #
      #   query = datastore.query("Task")
      #   tasks = datastore.run query
      #
      #   tasks.size #=> 3
      #   tasks.cursor #=> Gcloud::Datastore::Cursor(c3VwZXJhd2Vzb21lIQ)
      #
      # @example Caution, many Array methods will return a new Array instance:
      #   require "gcloud"
      #
      #   gcloud = Gcloud.new
      #   datastore = gcloud.datastore
      #
      #   query = datastore.query("Task")
      #   tasks = datastore.run query
      #
      #   tasks.size #=> 3
      #   tasks.end_cursor #=> Gcloud::Datastore::Cursor(c3VwZXJhd2Vzb21lIQ)
      #   descriptions = tasks.map { |task| task["description"] }
      #   descriptions.size #=> 3
      #   descriptions.cursor #=> NoMethodError
      #
      class QueryResults < DelegateClass(::Array)
        ##
        # The end_cursor of the QueryResults.
        #
        # @return [Gcloud::Datastore::Cursor]
        attr_reader :end_cursor
        alias_method :cursor, :end_cursor

        ##
        # The state of the query after the current batch.
        #
        # Expected values are:
        #
        # * `:NOT_FINISHED`
        # * `:MORE_RESULTS_AFTER_LIMIT`
        # * `:MORE_RESULTS_AFTER_CURSOR`
        # * `:NO_MORE_RESULTS`
        attr_reader :more_results

        ##
        # @private
        attr_accessor :service, :namespace, :cursors, :query

        ##
        # @private
        attr_writer :end_cursor, :more_results

        ##
        # Convenience method for determining if the `more_results` value
        # is `:NOT_FINISHED`
        def not_finished?
          more_results == :NOT_FINISHED
        end

        ##
        # Convenience method for determining if the `more_results` value
        # is `:MORE_RESULTS_AFTER_LIMIT`
        def more_after_limit?
          more_results == :MORE_RESULTS_AFTER_LIMIT
        end

        ##
        # Convenience method for determining if the `more_results` value
        # is `:MORE_RESULTS_AFTER_CURSOR`
        def more_after_cursor?
          more_results == :MORE_RESULTS_AFTER_CURSOR
        end

        ##
        # Convenience method for determining if the `more_results` value
        # is `:NO_MORE_RESULTS`
        def no_more?
          more_results == :NO_MORE_RESULTS
        end

        ##
        # @private Create a new QueryResults with an array of values.
        def initialize arr = []
          super arr
        end

        ##
        # Whether there are more results available.
        #
        # @return [Boolean]
        #
        # @example
        #   require "gcloud"
        #
        #   gcloud = Gcloud.new
        #   datastore = gcloud.datastore
        #   query = datastore.query "Task"
        #   tasks = datastore.run query
        #
        #   if tasks.next?
        #     next_tasks = tasks.next
        #   end
        #
        def next?
          !no_more?
        end

        ##
        # Retrieve the next page of results.
        #
        # @return [QueryResults]
        #
        # @example
        #   require "gcloud"
        #
        #   gcloud = Gcloud.new
        #   datastore = gcloud.datastore
        #   query = datastore.query "Task"
        #   tasks = datastore.run query
        #
        #   if tasks.next?
        #     next_tasks = tasks.next
        #   end
        #
        def next
          return nil unless next?
          return nil if end_cursor.nil?
          ensure_service!
          query.start_cursor = cursor.to_grpc # should always be a Cursor...
          query_res = service.run_query query, namespace
          self.class.from_grpc query_res, service, namespace, query
        end

        ##
        # Retrieve the {Cursor} for the provided result.
        #
        # @param [Entity] result The entity object to get a cursor for.
        #
        # @return [Cursor]
        #
        # @example
        #   require "gcloud"
        #
        #   gcloud = Gcloud.new
        #   datastore = gcloud.datastore
        #   query = datastore.query "Task"
        #   tasks = datastore.run query
        #
        #   first_task = tasks.first
        #   first_cursor = tasks.cursor_for first_task
        #
        def cursor_for result
          cursor_index = index result
          return nil if cursor_index.nil?
          cursors[cursor_index]
        end

        ##
        # Calls the given block once for each result and cursor combination,
        # which are passed as parameters.
        #
        # An Enumerator is returned if no block is given.
        #
        # @yield [result, cursor] The block for accessing each query result and
        #   cursor.
        # @yieldparam [Entity] result The query result object.
        # @yieldparam [Cursor] cursor The cursor object.
        #
        # @return [Enumerator]
        #
        # @example
        #   require "gcloud"
        #
        #   gcloud = Gcloud.new
        #   datastore = gcloud.datastore
        #   query = datastore.query "Task"
        #   tasks = datastore.run query
        #   tasks.each_with_cursor do |task, cursor|
        #     puts "Task #{task.key.id} (#cursor)"
        #   end
        #
        def each_with_cursor
          return enum_for(:each_with_cursor) unless block_given?
          zip(cursors).each { |r, c| yield [r, c] }
        end

        ##
        # Retrieves all query results by repeatedly loading {#next} until
        # {#next?} returns `false`. Calls the given block once for each query
        # result, which is passed as the parameter.
        #
        # An Enumerator is returned if no block is given.
        #
        # This method may make several API calls until all query results are
        # retrieved. Be sure to use as narrow a search criteria as possible.
        # Please use with caution.
        #
        # @param [Integer] request_limit The upper limit of API requests to make
        #   to load all query results. Default is no limit.
        # @yield [result] The block for accessing each query result.
        # @yieldparam [Entity] result The query result object.
        #
        # @return [Enumerator]
        #
        # @example Iterating each query result by passing a block:
        #   require "gcloud"
        #
        #   gcloud = Gcloud.new
        #   datastore = gcloud.datastore
        #   query = datastore.query "Task"
        #   tasks = datastore.run query
        #   tasks.all do |task|
        #     puts "Task #{task.key.id} (#cursor)"
        #   end
        #
        # @example Using the enumerator by not passing a block:
        #   require "gcloud"
        #
        #   gcloud = Gcloud.new
        #   datastore = gcloud.datastore
        #   query = datastore.query "Task"
        #   tasks = datastore.run query
        #   tasks.all.map(&:key).each do |key|
        #     puts "Key #{key.id}"
        #   end
        #
        # @example Limit the number of API calls made:
        #   require "gcloud"
        #
        #   gcloud = Gcloud.new
        #   datastore = gcloud.datastore
        #   query = datastore.query "Task"
        #   tasks = datastore.run query
        #   tasks.all(request_limit: 10) do |task|
        #     puts "Task #{task.key.id} (#cursor)"
        #   end
        #
        def all request_limit: nil
          request_limit = request_limit.to_i if request_limit
          unless block_given?
            return enum_for(:all, request_limit: request_limit)
          end
          results = self
          loop do
            results.each { |r| yield r }
            if request_limit
              request_limit -= 1
              break if request_limit < 0
            end
            break unless results.next?
            results = results.next
          end
        end

        ##
        # Retrieves all query results and cursors by repeatedly loading {#next}
        # until {#next?} returns `false`. Calls the given block once for each
        # result and cursor combination, which are passed as parameters.
        #
        # An Enumerator is returned if no block is given.
        #
        # This method may make several API calls until all query results are
        # retrieved. Be sure to use as narrow a search criteria as possible.
        # Please use with caution.
        #
        # @param [Integer] request_limit The upper limit of API requests to make
        #   to load all tables. Default is no limit.
        # @yield [result, cursor] The block for accessing each query result and
        #   cursor.
        # @yieldparam [Entity] result The query result object.
        # @yieldparam [Cursor] cursor The cursor object.
        #
        # @return [Enumerator]
        #
        # @example Iterating all results and cursors by passing a block:
        #   require "gcloud"
        #
        #   gcloud = Gcloud.new
        #   datastore = gcloud.datastore
        #   query = datastore.query "Task"
        #   tasks = datastore.run query
        #   tasks.all_with_cursor do |task, cursor|
        #     puts "Task #{task.key.id} (#cursor)"
        #   end
        #
        # @example Using the enumerator by not passing a block:
        #   require "gcloud"
        #
        #   gcloud = Gcloud.new
        #   datastore = gcloud.datastore
        #   query = datastore.query "Task"
        #   tasks = datastore.run query
        #   tasks.all_with_cursor.count #=> number of result/cursor pairs
        #
        # @example Limit the number of API calls made:
        #   require "gcloud"
        #
        #   gcloud = Gcloud.new
        #   datastore = gcloud.datastore
        #   query = datastore.query "Task"
        #   tasks = datastore.run query
        #   tasks.all_with_cursor(request_limit: 10) do |task, cursor|
        #     puts "Task #{task.key.id} (#cursor)"
        #   end
        #
        def all_with_cursor request_limit: nil
          request_limit = request_limit.to_i if request_limit
          unless block_given?
            return enum_for(:all_with_cursor, request_limit: request_limit)
          end
          results = self

          loop do
            results.zip(results.cursors).each { |r, c| yield r, c }
            if request_limit
              request_limit -= 1
              break if request_limit < 0
            end
            break unless results.next?
            results = results.next
          end
        end

        ##
        # @private New Dataset::QueryResults from a
        # Google::Dataset::V1beta3::RunQueryResponse object.
        def self.from_grpc query_res, service, namespace, query
          r, c = Array(query_res.batch.entity_results).map do |result|
            [Entity.from_grpc(result.entity), Cursor.from_grpc(result.cursor)]
          end.transpose
          r ||= []
          c ||= []
          new(r).tap do |qr|
            qr.cursors = c
            qr.end_cursor = Cursor.from_grpc query_res.batch.end_cursor
            qr.more_results = query_res.batch.more_results
            qr.service = service
            qr.namespace = namespace
            qr.query = query_res.query || query
          end
        end

        protected

        ##
        # @private Raise an error unless an active connection to the service is
        # available.
        def ensure_service!
          msg = "Must have active connection to datastore service to get next"
          fail msg if @service.nil? || @query.nil?
        end
      end
    end
  end
end