Indexes: Indexing Compare Exchange Values

• Compare exchange values can be loaded within an index using the value's key.

• The index will update when the compare exchange value is updated, as well as when documents are modified in the indexed collection(s).

• In this page:

  • Syntax
  • Examples
  • Querying the Index

Syntax

When creating an index using AbstractIndexCreationTask, use the method LoadCompareExchangeValue() to load a compare exchange value by its key.

//Load one compare exchange value
T LoadCompareExchangeValue<T>(string key);

//Load multiple compare exchange values
T[] LoadCompareExchangeValue<T>(IEnumerable<string> keys);

For javascript indexes, use the method cmpxchg(<key>).

Parameter	Type	Description
key	string	The key of a particular compare exchange value.
keys	IEnumerable<string>	The keys of multiple compare exchange values.

Examples

These indexes map the rooms in a hotel, as well as compare exchange values representing the guests in those rooms.

• LINQ-syntax
• JavaScript-syntax

private class Compare_Exchange_Index : AbstractIndexCreationTask<HotelRoom>
{
  public class Result
  {
      public string Room;
      public string Guests;
  }

  public Compare_Exchange_Index()
  {
      Map = HotelRooms => from room in HotelRooms
                          let guests = LoadCompareExchangeValue<string>(room.RoomID)
                          select new Result
                          {
                              Room = room.RoomID,
                              Guests = guests
                          };
  }
}

private class Compare_Exchange_JS_Index : AbstractJavaScriptIndexCreationTask
{
  public Compare_Exchange_JS_Index()
  {
      Maps = new HashSet<string>
      {
          @"map('HotelRooms', function (room) { 
              var guests = cmpxchg(room.RoomID); 
              return { 
                  RoomID: room.RoomID, 
                  Guests: guests 
              };
          })",
      };
  }
}

Querying the Index

• Sync
• Async
• RawQuery

// Return all vacant hotel rooms
List<HotelRoom> vacantRooms = session
  .Query<HotelRoom, Compare_Exchange_Index>()
  .Where(x => RavenQuery.CmpXchg<string>(x.RoomID) == null)
  .OfType<HotelRoom>()
  .ToList();

// Return all vacant hotel rooms
List<HotelRoom> vacantRooms = await asyncSession
  .Query<HotelRoom, Compare_Exchange_Index>()
  .Where(x => RavenQuery.CmpXchg<string>(x.RoomID) == null)
  .OfType<HotelRoom>()
  .ToListAsync();

// Return the room occupied by VIP guests
List<HotelRoom> VIPRooms = session
  .Advanced.RawQuery<HotelRoom>(
      @"from Hotelrooms as room
      where room.Guests == cmpxchg('VIP')"
  )
  .ToList();