CODEWITHSUNDEEP
c#mediatormediatr
ca9163d9
ca9163d9

Reputation: 29209

How is Mediatr wired?

Update:

The Mediatr in the project is used without any customized logic for dispatching the messages. Can I say it's used as an event aggregator?

In the source code of https://github.com/JasonGT/NorthwindTraders, the Controller gets the Mediator from ControllerBase.

[ApiController]
[Route("api/[controller]/[action]")]
public abstract class BaseController : ControllerBase
{
    private IMediator _mediator;

    protected IMediator Mediator => _mediator ??= HttpContext.RequestServices.GetService<IMediator>();
}

In the controller, it calls Mediator.Send(...) to send the message to the mediator.

public class EmployeesController : BaseController
{
    // ....
    [HttpGet("{id}")]
    [ProducesResponseType(StatusCodes.Status200OK)]
    public async Task<ActionResult<EmployeeDetailVm>> Get(int id)
    {
        return Ok(await Mediator.Send(new GetEmployeeDetailQuery { Id = id }));
    }

And the method Handle() in the inner class GetEmployeeDetailQuery.GetEmployeeDetailQueryHandler will be called for query message GetEmployeeDetailQuery. How is this wired? 

public class GetEmployeeDetailQuery : IRequest<EmployeeDetailVm>
{
    public int Id { get; set; }

    public class GetEmployeeDetailQueryHandler : IRequestHandler<GetEmployeeDetailQuery, EmployeeDetailVm>
    {
        private readonly INorthwindDbContext _context;
        private readonly IMapper _mapper;

        public GetEmployeeDetailQueryHandler(INorthwindDbContext context, IMapper mapper)
        {
            _context = context;
            _mapper = mapper;
        }

        public async Task<EmployeeDetailVm> Handle(GetEmployeeDetailQuery request, CancellationToken cancellationToken)
        {
            var vm = await _context.Employees
                .Where(e => e.EmployeeId == request.Id)
                .ProjectTo<EmployeeDetailVm>(_mapper.ConfigurationProvider)
                .SingleOrDefaultAsync(cancellationToken);

            return vm;
        }
    }
}

Upvotes: 0

Views: 338

Answers (1)

Jonathon Chase
Jonathon Chase

Reputation: 9704

In the startup.cs of that project, there's a call to AddApplication, which is an extension method from the NorthwindTraders.Application project, and is defined in DependencyInjection.cs. This calls services.AddMediatR(Assembly.GetExecutingAssembly());, which scans the assembly for handlers and registers them.

In general, you can register MediatR for your own projects by calling services.AddMediatr(Assembly.GetExecutingAssembly()) in your web application's Startup.ConfigureServices method.

Upvotes: 1

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