Introduction to MediatR

Presentation made at Criteo Full-Stack Tech Talks meetup!

Abstract:
CQRS, Messaging Handling, you do it in your .Net Core project and you don’t know MediatR?
This library developed by the American MVP Jimmy Bogard contains everything you need to organize your project correctly. In this presentation, we will focus on the issue dealt with by MediatR.
We will then discuss the capabilities of the library and its implementation to craft microservices in DDD.

Transcript

1. Criteo FullStack Tech Talks March, 2019
   

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2. Premier Field Engineer
   @spontoreau
   In ❤️ with
   Co-organizer
   

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5. Mediator
   obj obj
   obj obj
   obj obj
   obj obj
   

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7. Query
   Just a read operation
   Command
   Data validation
   Business logic
   Persistance
   

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8. GetOrderById
   Query
   UpdateProduct
   Command
   GetProducts
   Query
   DeleteOrder
   Command
   … …
   Dispatcher
   QueryHandler
   Read
   DB
   Dispatcher
   QueryHandler
   QueryHandler
   QueryHandler
   QueryHandler
   QueryHandler
   CommandHandler
   CommandHandler
   CommandHandler
   CommandHandler
   CommandHandler
   CommandHandler
   Write
   DB
   

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9. public class GetUserById : IRequest
   {
   public Guid Id { get; }
   public GetUserById(Guid id)
   {
   Id = id;
   }
   }
   public class DeleteUser : IRequest
   {
   public Guid Id { get; }
   public DeleteUser(Guid id)
   {
   Id = id;
   }
   }
   

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10. public class GetUserByIdHandler : IRequestHandler
    {
    public Task Handle(GetUserById request, CancellationToken cancellationToken)
    {
    // …
    }
    }
    

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11. IServiceCollection services = new ServiceCollection();
    services.AddMediatR(typeof(Startup).GetTypeInfo().Assembly);
    IServiceProvider provider = services.BuildServiceProvider();
    IMediator mediator = provider.GetService();
    User user = mediator.send(new GetUserById(
    "052ee87a-8ff5-4aa6-8f0d-3cd417e34e74"
    ));
    

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13. https://github.com/jbogard/MediatR
    https://ardalis.com/using-mediatr-in-aspnet-core-apps
    https://en.wikipedia.org/wiki/Mediator_pattern
    https://www.martinfowler.com/bliki/CQRS.html
    https://docs.microsoft.com/en-us/azure/architecture/patterns/cqrs
    https://github.com/spontoreau/MediatorPatternExample
    https://github.com/spontoreau/DemoMediatR
    

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