MediatR with .NET

Wolf Fact: Wolf pups are born blind and deaf. They gradually begin to see after 9 to 12 days and hear after around 4 weeks.

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Prerequisites: C#, basic Web API, Visual Studio

Mediator Pattern - The mediator pattern ensures that objects do not interact directly instead of through a mediator. It reduces coupling between objects which makes it easy to maintain the code. Mediator pattern unified the service interfaces around a common design, one request in, one response out.

MediatR is a simple, unambitious mediator implementation in .NET.

Let’s now dive deeper into the workings of a simple web API with MediatR. The complete code can be found here.

1. Create a new web API project.

OpenAPI support makes it easy to test the API.

1. Create a folder with these three classes.

Solution Hierarchy

2.1. ApiRequestModel: This class represents a request for API.

ApiRequestModel

IRequest<> It binds a request with a response.

2.2. ApiResponseModel: This class represents an API response.

ApiResponseModel

2.3. ApiHandler: And this class keeps the logical part.

ApiHandler

IRequesthandler<,> binds request and response with handler class. The logic of API is kept in the Handle method.

We will simply take a number as input and pass it to the response.

1. Now let’s check the controller. I wrote a base controller that other controllers would inherit.

ApiControllerBase

ISender is responsible for communication between different mediator-linked objects. It sends a request through a mediator pipeline to be handled by a single handler.

In this code, HomeController is inheriting the base controller. ApiController communicates with ApiHandler based on the ApiRequestModel and ApiResponseModel, pair.

ApiController

Now, Let's run the solution. You can test this API using Swagger(OpenAPI).

The above example illustrates the separation of request, response, logic, and communication using MediatR. If you want to move to the CQRS(Command and Query Responsibility Segregation) pattern, the mediator makes the transition seamless.

From version 9.0 the IMediator interface is split into two interfaces – ISender and IPublisher. These two new interfaces provide more strict access. ISender to send request and IPublisher for notification.

Any feedback would be greatly appreciated. Thank you.