How To Implement Mongodb TextSearch with C#

First add text index to the collection.

// add text index to the item
 string[] textIndex = new string[] { "Name", "ListItem.Name", "ListItem.Name2", "AnotherListItem.Name"};
            string indexName = string.Join("_text_", textIndex) + "_text";
            if (collection.IndexExistsByName(indexName))
            {
                collection.DropIndexByName(indexName);
            }
            collection.EnsureIndex(new IndexKeysBuilder().Text(textIndex));

Now, call text search functions

  var textSearchCommand = new CommandDocument
            {
              { "text", "CollectionName" },
              { "search", yourSearchTargetText}
            };

            var commandResult = Mongo.Database.RunCommand(textSearchCommand);
            var yourCollectionItems = commandResult.Response["results"].AsBsonArray.Select(o => 
            {
                return BsonSerializer.Deserialize(o["obj"].AsBsonDocument);
            });

Mongodb need to be 2.6 or higher

That's it, now you can enjoy text search in MongoDB.