using System;

public class Program

{

    public static void Main()

    {

        string sql = @"declare @RootDocumentId int = {0};WITH allDocs (title, id, level, parent_id, mimetype, ExternalId) 

                            AS

                             (

                                SELECT title, id, 1, NULL, mimetype, ExternalId FROM GDocumentDatas where Document_Id = @RootDocumentId

                                    UNION ALL

                                SELECT gd.title, gd.id, c.level + 1, c.id, gd.mimetype, gd.ExternalId

                                    FROM allDocs c

                                    INNER JOIN GDocumentDatas gd on gd.GDocumentData_Id = c.id

                                    --and level < 5

                                    where gd.IsDeleted = 0

                            )

​

                            select ExternalId from allDocs where mimetype <> 'folder' and ExternalId is not NULL";

​

            List<string> AllExternalIds = IRISEntityProvider.CurrentContext.Database.SqlQuery<string>(String.Format(sql, id)).ToList();

    }

}