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: / opt / td-agent / embedded / lib / ruby / gems / 2.1.0 / gems / mongo-2.2.7 / lib / mongo / operation /
Filename : read_preference.rb
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# Copyright (C) 2014-2015 MongoDB, Inc.
#
# 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.

module Mongo
  module Operation

    # Adds behaviour for updating the options and the selector for operations
    # that need to take read preference into account.
    #
    # @since 2.0.0
    module ReadPreference

      # The constant for slave ok flags.
      #
      # @since 2.0.6
      SLAVE_OK = :slave_ok

      private

      def update_selector(context)
        if context.mongos? && read_pref = read.to_mongos
          sel = selector[:$query] ? selector : { :$query => selector }
          sel.merge(:$readPreference => read_pref)
        else
          selector
        end
      end

      def slave_ok?(context)
        (context.cluster.single? && !context.mongos?) || read.slave_ok?
      end

      def update_options(context)
        if slave_ok?(context)
          options.dup.tap do |opts|
            (opts[:flags] ||= []) << SLAVE_OK
          end
        else
          options
        end
      end

      def message(context)
        sel = update_selector(context)
        opts = update_options(context)
        Protocol::Query.new(db_name, query_coll, sel, opts)
      end
    end
  end
end