Beginners' guide to using MongoDB 4.0.2 and the official C# driver

namespace TestMongo
{
    using System;
    using System.IO;
    using System.Linq;

    using MongoDB.Bson;
    using MongoDB.Driver;
    using MongoDB.Driver.Builders;
    using MongoDB.Driver.GridFS;

    public partial class Program
    {
        #region Public Methods and Operators

        public static void DemoGridFS(MongoDatabase database)
        {
            var assemblyPath = System.Reflection.Assembly.GetExecutingAssembly().Location;
            var directoryName = Path.GetDirectoryName(assemblyPath);
            string fullyQualifiedUpLoadName = directoryName+@"\Images\mars.png";

            //The uploaded file name equals fullyQualifiedUpLoadName
            MongoGridFSFileInfo gridFsInfo = database.GridFS.Upload(fullyQualifiedUpLoadName);

            //Here the uploaded file is given the name 'mars.png'
            using (var fs = new FileStream(fullyQualifiedUpLoadName, FileMode.Open))
            {
                database.GridFS.Upload(fs, "mars.png");
            }
            // Add metadata to facilitate searching.
            var photoMetadata = new BsonDocument
            { { "Category", "Astronomy" }, { "SubGroup", "Planet" }, { "ImageWidth", 640 }, { "ImageHeight", 480 } };

            database.GridFS.SetMetadata(gridFsInfo, photoMetadata);

            //Build an index to search the metadata
            MongoCollection<BsonDocument> coll = database.GetCollection("fs.files");
            IndexKeysBuilder keys = IndexKeys.Ascending("metadata.Category", "metadata.SubGroup");

            //Add an optional name- useful for admin
            IndexOptionsBuilder options = IndexOptions.SetName("PhotoIndex");

            //This locks the database while the index is being built
            coll.EnsureIndex(keys, options);

            //Search using the PhotoIndex
            MongoCursor<MongoGridFSFileInfo> astronomyPics =
                database.GridFS.Find(Query.EQ("metadata.Category", "Astronomy"));

            //use a filename to download.
             string fullyQualifiedDownLoadName = directoryName + @"\Images\mars2.png"; ;
            database.GridFS.Download(fullyQualifiedDownLoadName, fullyQualifiedUpLoadName);

            MongoCursor<MongoGridFSFileInfo> filesInfo = database.GridFS.FindAll();
            if (filesInfo.Any())
            {
                Console.WriteLine("The following files have been uploaded.");
            }
            foreach (MongoGridFSFileInfo fileInfo in filesInfo)
            {
                Console.WriteLine(
                    "Name {0} size {1} uploaded on {2}",
                    fileInfo.Name,
                    fileInfo.Length,
                    fileInfo.UploadDate.ToShortDateString());
            }

            //  database.GridFS.Delete(fullyQualifiedUpLoadName);
            //  database.GridFS.Delete("mars.png");
        }

        #endregion
    }
}