using Microsoft.AspNetCore.SignalR;
using SignalR5.BusinessLogic;
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Threading.Tasks;

namespace SignalR5.Hubs
{
    
    public class CallNotificationHub : Hub
    {
        //
        //  https://docs.microsoft.com/en-us/aspnet/core/signalr/hubs?view=aspnetcore-5.0
        //  https://docs.microsoft.com/en-us/aspnet/core/signalr/hubs?view=aspnetcore-5.0
        //
        private SqlDependency dependency;

        //  public Task OnConnected()
        public override async Task OnConnectedAsync()
        {
            //return base.OnConnectedAsync();
            await base.OnConnectedAsync();
        }

        

        //[HubMethodName("sendCallNotifications")]
        public async Task SendCallNotifications()
        {

            try
            {
                string connectionString = "server=(local);uid=sa;pwd=;database=myDB";
                SqlDependency.Start(connectionString);
                SqlConnection connection = new SqlConnection(connectionString);
                connection.Open();

                SqlCommand command = new SqlCommand();
                command.CommandText = "SELECT [ID], [TimeEntered], [CallFrom], [CallTo] FROM [dbo].[tbl_Log_InboundTwilioCalls]";
                command.Connection = connection;
                command.CommandType = CommandType.Text;

                dependency = new SqlDependency(command);
                dependency.OnChange += new OnChangeEventHandler(dependency_OnChange);

                DataTable dt = new DataTable();

                dependency.AddCommandDependency(command);

                var reader = command.ExecuteReader();

                SendEmail sendEmail = new SendEmail("SendCallNotifications Reached", "New SignalR5 SendCallNotifications at " + DateTime.Now.ToString(), "");

                //await Clients.All.SendAsync("ReceiveMessage", "user", "message");
            }
            catch (Exception ex)
            {
                SendEmail sendErrEmail = new SendEmail("SendCallNotifications Error", ex.ToString(), "");
            }

            //await Clients.All.SendAsync("RecieveNotification", "Changed");
            await Clients.All.SendAsync("RecieveNotification", "Changed at " + DateTime.Now.ToString());

        }

        private void dependency_OnChange(object sender, SqlNotificationEventArgs e)
        {
            SendEmail sendEmail = new SendEmail("Dependency Change", e.Type.ToString() + " at " + DateTime.Now.ToString(), "");
            if (e.Type == SqlNotificationType.Change)
            {                
                CallNotificationHub nHub = new CallNotificationHub();
                nHub.SendCallNotifications();
            }
        }
    }
}

And the client code

"use strict";

var connection = new signalR.HubConnectionBuilder().withUrl("/CallNotificationHub").build();

connection.on("RecieveNotification", (result) => {
    //var li = document.createElement("li");
    //li.textContent = result;
    //document.getElementById("messagesList").appendChild(li);

    console.log(result);
    alert("Changed");
});

connection.start().then(function () {
    connection.invoke("SendCallNotifications").catch(err => console.error(err));
}).catch(function (err) {
    return console.error(err.toString());
});