Full text search in mongodb in .net

I could create text indexes with this command:

collection.Indexes.CreateOne(Builders<searchFileByAuthor>.IndexKeys.Text(x=>x.subject));

And than i could query index this way:

collection.Find(Builders<searchFileByAuthor>.Filter.Text("coffe")).ToList();

searchFileByAuthor is just my fake class with subject field:

public class searchFileByAuthor
{
    public int Id { get; set; } 
    public string subject { get; set; } 
}

Maksim Simkin answer is correct, althought it is obsolete. The updated version would be:

collection.Indexes.CreateOne(new CreateIndexModel<YourClass>(Builders<YourClass>.IndexKeys.Text(x => x.something)));

or, if you would like to use the Wildcard Indexing (to index the entire document), you could do like this:

collection.Indexes.CreateOne(new CreateIndexModel<YourClass>(Builders<YourClass>.IndexKeys.Text("$**")));

or maybe you want/have more indexes for some reason, than do this:

var indexWildcardTextSearch = new CreateIndexModel<YourClass>(Builders<YourClass>.IndexKeys.Text("$**"));

List<CreateIndexModel<YourClass>> indexes = new List<CreateIndexModel<YourClass>>();
indexes.Add(indexWildcardTextSearch);

collection.Indexes.CreateMany(indexes);

And to query, it remains the same:

collection.Find(Builders<YourClass>.Filter.Text("something")).ToList();