def update_item!(updates, options = {})
      item_updates = []
      updates.each do |attribute, value|
        item_field = FIELD_URIS[attribute][:text] if FIELD_URIS.include? attribute
        field = {field_uRI: {field_uRI: item_field}}

        if value.nil? && item_field
          # Build DeleteItemField Change
          item_updates << {delete_item_field: field}
        elsif item_field
          # Build SetItemField Change
          item = Viewpoint::EWS::Template::CalendarItem.new(attribute => value)

          # Remap attributes because ews_builder #dispatch_field_item! uses #build_xml!
          item_attributes = item.to_ews_item.map do |name, value|
            if value.is_a? String
              {name => {text: value}}
            elsif value.is_a? Hash
              node = {name => {}}
              value.each do |attrib_key, attrib_value|
                attrib_key = camel_case(attrib_key) unless attrib_key == :text
                node[name][attrib_key] = attrib_value
              end
              node
            else
              {name => value}
            end
          end

          item_updates << {set_item_field: field.merge(calendar_item: {sub_elements: item_attributes})}
        else
          # Ignore unknown attribute
        end
      end

      if item_updates.any?
        data = {}
        data[:conflict_resolution] = options[:conflict_resolution] || 'AutoResolve'
        data[:send_meeting_invitations_or_cancellations] = options[:send_meeting_invitations_or_cancellations] || 'SendToNone'
        data[:item_changes] = [{item_id: self.item_id, updates: item_updates}]
        rm = ews.update_item(data).response_messages.first
        if rm && rm.success?
          self.get_all_properties!
          self
        else
          raise EwsCreateItemError, "Could not update calendar item. #{rm.code}: #{rm.message_text}" unless rm
        end
      end

    end
def update_item!(updates, options = {})
      item_updates = []
      updates.each do |attribute, value|
        item_field = FIELD_URIS[attribute][:text] if FIELD_URIS.include? attribute
        field = {field_uRI: {field_uRI: item_field}}

        if value.nil? && item_field
          # Build DeleteItemField Change
          item_updates << {delete_item_field: field}
        elsif item_field
          # Build SetItemField Change
          item = Viewpoint::EWS::Template::CalendarItem.new(attribute => value)

          # Remap attributes because ews_builder #dispatch_field_item! uses #build_xml!
          item_attributes = item.to_ews_item.map do |name, value|
            if value.is_a? String
              {name => {text: value}}
            elsif value.is_a? Hash
              node = {name => {}}
              value.each do |attrib_key, attrib_value|
                attrib_key = camel_case(attrib_key) unless attrib_key == :text
                node[name][attrib_key] = attrib_value
              end
              node
            else
              {name => value}
            end
          end

          item_updates << {set_item_field: field.merge(calendar_item: {sub_elements: item_attributes})}
        else
          # Ignore unknown attribute
        end
      end

      if item_updates.any?
        data = {}
        data[:conflict_resolution] = options[:conflict_resolution] || 'AutoResolve'
        data[:send_meeting_invitations_or_cancellations] = options[:send_meeting_invitations_or_cancellations] || 'SendToNone'
        data[:item_changes] = [{item_id: self.item_id, updates: item_updates}]
        rm = ews.update_item(data).response_messages.first
        if rm && rm.success?
          self.get_all_properties!
          self
        else
          raise EwsCreateItemError, "Could not update calendar item. #{rm.code}: #{rm.message_text}" unless rm
        end
      end

    end
Updates the specified item attributes

 Uses `SetItemField` if value is present and `DeleteItemField` if value is nil
 @param updates [Hash] with (:attribute => value)
 @param options [Hash]
 @option options :conflict_resolution [String] one of 'NeverOverwrite', 'AutoResolve' (default) or 'AlwaysOverwrite'
 @option options :send_meeting_invitations_or_cancellations [String] one of 'SendToNone' (default), 'SendOnlyToAll',
   'SendOnlyToChanged', 'SendToAllAndSaveCopy' or 'SendToChangedAndSaveCopy'
 @return [CalendarItem, false]
 @example Update Subject and Body
   item = #...
   item.update_item!(subject: 'New subject', body: 'New Body')
 @see http://msdn.microsoft.com/en-us/library/exchange/aa580254.aspx
 @todo AppendToItemField updates not implemented