public List <TField> Distinct <TField>(Expression <Func <TEntity, TField> > fieldExp, FilterDefinition <TEntity> filter, ReadPreference readPreference = null)
{
if (filter == null)
{
filter = Filter.Empty;
}
return(IAsyncCursorExtensions.ToList <TField>(IMongoCollectionExtensions.Distinct <TEntity, TField>(GetCollection(readPreference), fieldExp, filter, null)));
}