CommandScheduler 2.2.2

Integrate MediatR with Hangfire

To schedule your commands, execute them parallel with the retry option and monitor them. Hangfire gives me all these kinds of features but You have to have public method which You have to pass to Hangifre method (for example BackgroundJob.Enqueue). This is a problem – with the mediator pattern You cannot pass the public method of the handler because You have decoupled it from the invoker. So You need a special way to integrate MediatR with Hangfire without affecting basic assumptions.

I presented the way of processing commands asynchronously using MediatR and Hangfire. With this approach we have:

1. Decoupled invokers and handlers of commands.
2. Scheduling commands mechanism.
3. Invoker and handler of command may be other processes.
4. Commands execution monitoring.
5. Commands execution retries mechanism.

These benefits are very important during development using an eventual consistency approach. We have more control over command processing and we can react quickly if a problem will appear.

For this, In CommandScheduler we defined 4 classes:

• CommandsScheduler serializes commands and sends them to Hangfire.
• CommandsExecutor responds to Hangfire jobs execution, deserializes commands, and sends them to handlers using MediatR.
• MediatorSerializedObject wrapper class for serialized/deserialized commands with additional properties – command type and additional description.
• MediatorExtension extension methods for IMediator

public class MyMController : Controller
{
    private IMediator _mediator;
    
    public MyMicroserviceController(IMediator mediator)
    {
        _mediator = mediator;
    }
    
    [HttpPost]
    public async Task<IActionResult> Post([FromBody] TestCommand testCommand)
    {
      // Executed after a certain time interval
      _mediator.Schedule(new Command { Id = 1 }, DateTimeOffset.Now.AddSeconds(5));

      // Fire many times on the specified CRON schedule
      //_mediator.ScheduleRecurring(new Command { Id = 1 },nameof(Command), CommonCrons.Minutely);

      // Executed only once and almost immediately after creation
      //_mediator.Enqueue(new Command { Id = 1 });

        return Ok();
    }

And our commands are scheduled, invoked, and monitored by Hangfire.

Installation

Install the package via NuGet first: Install-Package CommandScheduler

Or via the .NET Core command line interface: dotnet add package CommandScheduler

Either commands, from Package Manager Console or .NET Core CLI, will download and install CommandScheduler and all required dependencies.

The CommandScheduler includes a IServiceCollection.AddCommandsScheduler(Connection, Assembly) extension method, allowing you to register CommandScheduler.

builder.Services.AddCommandsScheduler(builder.Configuration.GetConnectionString("HangfireConnection"), typeof(Program));