Program.cs

using CommandLine;
using Google.Cloud.Firestore;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace GoogleCloudSamples
{
    public class QuickStartFirestoreProgram
    {
        public static string Usage = @"Usage:
C:\> dotnet run command project
C:\> dotnet run command my-project-id

Where command is one of
    update-nested-fields
";
        private static async Task UpdateNestedFields(string project)
        {
            FirestoreDb db = FirestoreDb.Create(project);
            // [START fs_update_nested_fields]
            DocumentReference frankDocRef = db.Collection("users").Document("frank");
            Dictionary<string, object> initialData = new Dictionary<string, object>
            {
                { "Name", "Frank" },
                { "Age", 12 }
            };

            Dictionary<string, object> favorites = new Dictionary<string, object>
            {
                { "Food", "Pizza" },
                { "Color", "Blue" },
                { "Subject", "Recess" },
            };
            initialData.Add("Favorites", favorites);
            WriteResult initialResult = await frankDocRef.SetAsync(initialData);
            
            // Update age and favorite color
            Dictionary<FieldPath, object> updates = new Dictionary<FieldPath, object>
            {
                { new FieldPath("Age"), 13 },
                { new FieldPath("Favorites.Color"), "Red" },
            };

            // Asynchronously update the document
            WriteResult updateResult = await frankDocRef.UpdateAsync(updates);
            Console.WriteLine(updateResult.UpdateTime);
            // [END fs_update_nested_fields]
            Console.WriteLine("Updated the age and favorite color fields of the Frank document in the users collection.");
        }

        public static void Main(string[] args)
        {
            if (args.Length < 2)
            {
                Console.Write(Usage);
                return;
            }
            string command = args[0].ToLower();
            string project = string.Join(" ",
                new ArraySegment<string>(args, 1, args.Length - 1));
            switch (command)
            {
                case "update-nested-fields":
                    UpdateNestedFields(project).Wait();
                    break;

                default:
                    Console.Write(Usage);
                    return;
            }
        }
    }
}