How to implement MySQL table change notification in ASP.NET Core/SignalR?

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To implement MySQL table change notification in ASP.NET Core/SignalR, follow these steps:

1. Install the MySQL Connector/NET package using NuGet Package Manager.

2. Create a MySQL database and a table that you want to monitor for changes.

3. Create a .NET Core project and add the following packages to it:

   • Microsoft.AspNetCore.SignalR.Core
   • MySqlConnector

4. Add a class named ‘ChangeNotificationService’ to the project that will handle listening to the database for changes. This class will implement the ‘IDisposable’ interface and will use the MySqlConnector package installed earlier.

5. In the ‘ConfigureServices’ method of Startup.cs, add the following code to inject the ‘ChangeNotificationService’ as a singleton service:

   services.AddSingleton<changenotificationservice>();

6. In the same method, add the following code to add SignalR to the application:

   services.AddSignalR();

7. In the ‘Configure’ method of Startup.cs, add the following code to map the SignalR hub:

   app.UseEndpoints(endpoints => { endpoints.MapHub<notificationhub>("/notificationHub"); });

8. Create a SignalR hub named ‘NotificationHub’ that will handle broadcasting changes to connected clients. This hub will inherit from Microsoft.AspNetCore.SignalR.Hub.

9. In the ‘OnConnectedAsync’ method of the ‘NotificationHub’ class, add the following code to register the connected client:

   await notificationService.RegisterClientAsync(Context.ConnectionId);

10. In the same class, add a method that will handle the database change notification:

    [HubMethodName("Notify")] public void Notify(string tableName, string eventType) { Clients.All.SendAsync("Notify", tableName, eventType); }

11. In the ‘ChangeNotificationService’ class that was created earlier, add the following code to listen for database changes:

    private async Task ListenForChanges() { var connection = new MySqlConnection(connectionString);

    var command = new MySqlCommand("SELECT * FROM your_table", connection); var dependency = new MySqlDependency(command);

    dependency.OnChange += async (o, e) => await OnChangeAsync(e.EventArgs);

    await connection.OpenAsync(); await command.ExecuteNonQueryAsync(); }

12. In the above code, replace ‘your_table’ with the name of the table that you want to monitor for changes.

13. In the ‘OnChangeAsync’ method of the ‘ChangeNotificationService’ class, add the following code to notify the SignalR hub of any changes:

    await notificationHubContext.Clients.All.SendAsync( "Notify", e.Table.ToString(), e.Type.ToString());

14. In the above code, replace ‘e.Table.ToString()’ with the name of the table that you want to monitor for changes, and ‘e.Type.ToString()’ with the type of change (insert, update or delete).

15. Finally, to start listening for changes, add the following code in the ‘StartAsync’ method of the ‘ChangeNotificationService’ class:

    await ListenForChanges();

16. Run the application and connect to the SignalR hub using a JavaScript client or any other client of your choice. Whenever a change occurs in the monitored table, connected clients will be notified.