Step1.md

Step 1 - Setup the project

Create the Solution

• Create new, ASP.NET Core Web Api Project (c#, Linux, macOS, ...)
  • project name: QuestionsApp.Web
  • solution name: QuestionsApp
  • target framework: .NET 7.0
  • Authentication Type: None
  • Configure HTTPS: Not checked
  • Enable Docker: Not checked
  • Use controllers: Not checked
  • Enable OpenApi Support: Checked
  • Do not use top-level statements: Not checked
• Add new xUnit Test Project (c#, Linux, macOS, ...)
  • project name: QuestionsApp.Tests
  • target framework .NET 7.0
• Save all

Add the MediatR Nuget Package

• Add the MediatR Package to the QuestionsApp.Web Dependencies
• Save all

Add folders for the Web Api

• Add the folders in the QuestionsApp.Web project
  • Api
  • Api/Commands
  • Api/Queries

Add the GetQuestionsQuery class

Add a class GetQuestionsQuery in the Api/Queries/ folder

• Add using MediatR;
• Save the file

Add Request and Response Classes

Add the GetQuestionsResponse class with int ID, string Content, int Votes properies

public class GetQuestionsResponse
{
	public int ID { get; set; }
	public string Content { get; set; } = "";
	public int Votes { get; set; }
}

Add the GetQuestionsRequest class with IRequest<List<GetQuestionsResponse>> interface

public class GetQuestionsRequest : IRequest<List<GetQuestionsResponse>>
{ }

Setup the GetQuestionsQuery Request-Handler

Add the IRequestHandler<GetQuestionsRequest, List<GetQuestionsResponse>> interface to the GetQuestionsQuery class and add the empty implementation

public class GetQuestionsQuery : IRequestHandler<GetQuestionsRequest, List<GetQuestionsResponse>>
{
	public Task<List<GetQuestionsResponse>> Handle(GetQuestionsRequest request, CancellationToken cancellationToken)
	{
		throw new NotImplementedException();
	}
}

Add the AskQuestionCommand class

Add a class AskQuestionCommand in the Api/Commands/ folder

• Add using MediatR;
• Save the file

Add Request Class

Add the AskQuestionRequest class with IRequest<IResult> interface

public class AskQuestionRequest :IRequest<IResult>
{
	public string Content { get; set; } = "";
}

Setup the AskQuestionCommand Request-Handler

Add the IRequestHandler<AskQuestionRequest, IResult> interface to the AskQuestionCommand class and add the empty implementation

public class AskQuestionCommand : IRequestHandler<AskQuestionRequest, IResult>
{
	public Task<IResult> Handle(AskQuestionRequest request, CancellationToken cancellationToken)
	{
		throw new NotImplementedException();
	}
}

Add the VoteForQuestionCommand class

Add a class VoteForQuestionCommand in the Api/Commands/ folder

• Add using MediatR;
• Save the file

Add Request Class

Add the VoteForQuestionRequest class with IRequest<IResult> interface

public class VoteForQuestionRequest : IRequest<IResult>
{
	public int QuestionID { get; set; }
}

Setup the VoteForQuestionCommand Request-Handler

Add the IRequestHandler<VoteForQuestionRequest, IResult> interface to the VoteForQuestionCommand class and add the empty implementation

public class VoteForQuestionCommand : IRequestHandler<VoteForQuestionRequest, IResult>
{
	public Task<IResult> Handle(VoteForQuestionRequest request, CancellationToken cancellationToken)
	{
		throw new NotImplementedException();
	}
}

Setup Minimal API in Program.cs File

Clean Up example code

Remove the Example code (Summary, app.MapGet and WeatherForecast record

// remove summaries
var summaries = new[]
{
    "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
};

// remove MapGet
app.MapGet("/weatherforecast", () =>
{
    var forecast = Enumerable.Range(1, 5).Select(index =>
        new WeatherForecast
        (
            DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
            Random.Shared.Next(-20, 55),
            summaries[Random.Shared.Next(summaries.Length)]
        ))
        .ToArray();
    return forecast;
});

// remove WeatherForecast
internal record WeatherForecast(DateOnly Date, int TemperatureC, string? Summary)
{
    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);
}

Register MediatR Handlers

• Add using MediatR;

Add the MediatR Registration after builder.Services.AddSwaggerGen()

builder.Services.AddSwaggerGen();
// Register MediatR
builder.Services.AddMediatR(cfg => cfg.RegisterServicesFromAssemblyContaining<Program>());

Add Maps for Queries and Commands

• Add using QuestionsApp.Web.Api.Commands;
• Add using QuestionsApp.Web.Api.Queries;

Add the query and command maps before the app.Run() statement

// Queries
app.MapGet("api/queries/questions", async (IMediator mediator) 
    => await mediator.Send(new GetQuestionsRequest()));

// Commands
app.MapPost("api/commands/questions/", async (IMediator mediator, string content) 
    => await mediator.Send(new AskQuestionRequest { Content = content }));

app.MapPost("api/commands/questions/{id:int}/vote", async (IMediator mediator, int id) 
    => await mediator.Send(new VoteForQuestionRequest { QuestionID = id }));

app.Run();

---

Add Unittests for RequestHandlers

• Add a project refererence to the QuestionsApp.Web project in the QuestionsApp.Tests project
• Add the NuGet Package FluentAssertions
• Rename the Unittest1.cs file to QuestionsTests.cs
• Remove the Test1 Method in the QuestionsTests.cs
• Add using FluentAssertions;
• Add using QuestionsApp.Web.Api.Commands;
• Add using QuestionsApp.Web.Api.Queries;

Implement tests

Helper methods to create instances of the handlers

private GetQuestionsQuery GetQuestionsQueryHandler => new();
private AskQuestionCommand AskQuestionCommandHandler => new();
private VoteForQuestionCommand VoteForQuestionCommandHandler => new();

Empty Test

[Fact]
public async void Empty()
{
	var response = await GetQuestionsQueryHandler.Handle(new GetQuestionsRequest(), default);
	response.Should().BeEmpty();
}

OneQuestion

[Fact]
public async void OneQuestion()
{
	var askResponse = await AskQuestionCommandHandler.Handle(new AskQuestionRequest { Content = "Dummy Question" }, default);
	askResponse.Should().NotBeNull();

	var response = await GetQuestionsQueryHandler.Handle(new GetQuestionsRequest(), default);
	response.Should().HaveCount(1);
}

OneQuestionAndVote Test

[Fact]
public async void OneQuestionAndVote()
{
	var askResponse = await AskQuestionCommandHandler.Handle(new AskQuestionRequest { Content = "Dummy Question" }, default);
	askResponse.Should().NotBeNull();

	var response = await GetQuestionsQueryHandler.Handle(new GetQuestionsRequest(), default);
	response.Should().HaveCount(1);
	response[0].Votes.Should().Be(0);

	var voteResponse = await VoteForQuestionCommandHandler.Handle(new VoteForQuestionRequest { QuestionID = response[0].ID }, default);
	voteResponse.Should().NotBeNull();

	response = await GetQuestionsQueryHandler.Handle(new GetQuestionsRequest(), default);
	response.Should().HaveCount(1);
	response[0].Votes.Should().Be(1);
}