public async Task Update(Speaker speaker)
 {
     var mongoSpeaker = speaker as MongoSpeaker;
     await GetSpeakerCollection().ReplaceOneAsync(speaker1 => speaker1.DbId == mongoSpeaker.DbId, mongoSpeaker);
 }
 public async Task Update(Speaker speaker)
 {
     throw new NotImplementedException();
 }
 public async Task Add(Speaker speaker)
 {
     var mongoSpeaker = speaker as MongoSpeaker;
     await GetSpeakerCollection().InsertOneAsync(mongoSpeaker);
 }
 public async Task Add(Speaker speaker)
 {
     var result = await _client.CreateDocumentAsync(_collection.SelfLink, speaker);
     
 }