full watcher example

Program.cs

using MongoDB.Bson;
using MongoDB.Entities;
using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

namespace TestApplication
{
    public static class Program
    {
        public class Book : Entity
        {
            public string Title { get; set; }
        }

        private static async Task Main()
        {
            await DB.InitAsync("test", "localhost");

            var watcher = DB.Watcher<Book>("book-watcher");

            var cts = new CancellationTokenSource();

            watcher.OnChangesAsync += async books =>
            {
                Console.WriteLine(">>> received a batch!");

                foreach (var book in books)
                {
                    Console.WriteLine("--> " + book.Title);
                    await Task.Delay(500);

                    if (book.Title == "book 2")//stop the watcher after 2nd book is received.
                    {
                        //this will cause the OnStop event to fire enabling us to store the resume token there.
                        cts.Cancel();

                        //NOTE: OnStop is fired only at the end of the current batch!!!
                        //      so it will resume starting at book 6 when app restarts,
                        //      because our batchSize is 5.
                    }
                }
            };

            watcher.OnError += async exception =>
            {
                Console.WriteLine("error: " + exception.Message);

                if (watcher.CanRestart)
                {
                    watcher.ReStart();
                }
                else
                {
                    Console.WriteLine("your watch has ended (due to an error)");
                    await File.WriteAllTextAsync("resume.token", watcher.ResumeToken.ToJson());
                }
            };

            watcher.OnStop += async () =>
            {
                if (watcher.CanRestart)
                {
                    watcher.ReStart();
                }
                else
                {
                    Console.WriteLine("your watch has ended (due to stopping)");
                    Console.WriteLine("restart the app to resume from where it stopped...");
                    await File.WriteAllTextAsync("resume.token", watcher.ResumeToken.ToJson());
                }
            };

            if (File.Exists("resume.token"))
            {
                var resumeToken = BsonDocument.Parse(File.ReadAllText("resume.token"));

                watcher.StartWithToken(
                    resumeToken: resumeToken,
                    eventTypes: EventType.Created,
                    batchSize: 5,
                    cancellation: cts.Token);

                Console.WriteLine("watcher resumed with last saved token...");
            }
            else
            {
                watcher.Start(
                    eventTypes: EventType.Created,
                    batchSize: 5,
                    cancellation: cts.Token);

                Console.WriteLine("watcher started...");

                for (int i = 1; i <= 20; i++)
                {
                    await new Book { Title = $"book {i}" }.SaveAsync();
                }
            }

            await Task.Delay(10000);
            Console.WriteLine("press a key to exit!");
            Console.ReadLine();
        }
    }
}