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C# Async ops

El nucleo de la programacion asincrona son los objetos Task y Task<T>. Ambos son compatibles con las palabras clave async y await.

Primero hay que identificar si el codigo se usa para trabajos enlazados a I/O o si estos son CPU intensivos.

  • Si el codigo espera algo como una BBDD o una response de un servidor, es codigo I/O. En este caso hay que usar async y await
  • Si el codigo realiza un calculo costoso, es CPU intensivo. Use await para esperar una operacion que se ha comenzado en background con Task.run

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Mock multiple calls with same params

This is an example on how to mock a call when it’s called multiple times, and with the same parameter type every time.

Setup

I have the following class…

public class ConnectorRequest
{
	public string Query { get; set; }
}

… which will be consumed by the following service

public class IConnectorService
{
	Task<string> Execute(ConnectorRequest request);
}

Then I have a class which calls IConnectorService multiple times

public class ConnectorConsumerService
{
	private IConnectorService _service;
	
	// ...
	
	public async Task<string> Process() 
	{
		// ... does whatever
		var response1 = await _service.Execute(request1);
		// ... does whatever with that information
		var response2 = await _service.Execute(request2);
		// ... does whatever with that information
		var response3 = await _service.Execute(request3);
		// ... does whatever with that information
		// ... does whatever else
	}
	
	// ...
	
}

Test

Test which mocks multiple calls

public class ConnectorConsumerServiceTest
{
	// all mocks and stubs
	private Mock<IConnectorService> _dependencyMock;

	// service under test
	private ConnectorConsumerService _service;

	public ConnectorConsumerServiceTest()
	{
		_dependencyMock = new Mock<IConnectorService>();
		_service = new ConnectorConsumerService(_dependencyMock.Object);
	}

	[Fact]
	public async Task ProcessXXX_CaseXXX_ShouldReturnOkay()
	{
		// ARRANGE
		// example starts here! -> 
		var responseToExecution1 = new ConnectorRequest
		{
			Query = "some response";
		}
		var responseToExecution2 = new ConnectorRequest
		{
			Query = "another response";
		}
		var responseToExecution3 = new ConnectorRequest
		{
			Query = "oh no! a response";
		}
		
		_dependencyMock.SetupSequence(mock => mock.Execute(It.IsAny<ConnectorRequest>()))
			.ReturnsAsync(responseToExecution1)
			.ReturnsAsync(responseToExecution2)
			.ReturnsAsync(responseToExecution3);
		// <- example ends here

		// ACT
		var result = await _service.Process();
	
		// ASSERT
		result.status.Should().NotBeNull();
		// ... assert whatever
	}
}

XUnit test examples

Controller test example

this includes how to mock a request’s header - but it’s a bogus test. this only shows how to use XUnit and its structure.

public class XXXControllerTest
{
	// all mocks and stubs
	private Mock<IXXXService> _serviceMock;
	
	// controller under test 
	private XXXController _controller;
	
	public XXXControllerTest() 
	{
		_serviceMock = new Mock<IXXXService>();
		_controller = new XXXController(_serviceMock.Object);
	}
	
	[Fact]
	public async Task CallXXX_ShouldCall_Service()
	{
	// ARRANGE
	
	// mock header
	var httpContext = new DefaultHttpContext();
	httpContext.Request.Headers["someHeader"] = "my-mocked-value";
	_controller.ControllerContext = new ControllerContext
	{
		HttpContext = httpContext
	};
	
	// mock request
	string mockedValue = "someInputValueTo_serviceMock";
	string mockedResponse = "someResponseValueFrom_serviceMock";
	_serviceMock.Setup(mock => mock.SomeMethodCall(mockedValue)).ReturnsAsync(mockedResponse);
	
	// ACT
	var response = await _controller.CallSomething(mockedValue) as OkObjectResult;
	
	// ASSERT
	response.Should().NotBeNull();
	response.StatusCode.Should().Be(200);
	response.Value.Should().BeEquivalentTo(mockedResponse);
	}
}

Basic service test example

public class XXXServiceTest
{
	// all mocks and stubs
	private Mock<IXXXDependency> _dependency;

	// service under test
	private XXXService _serviceMock;

	public XXXServiceTest()
	{
		_dependency = new Mock<IXXXDependency>();
		_serviceMock = new XXXService(_dependency.Object);
	}

	[Fact]
	public async Task ProcessXXX_CaseXXX_ShouldReturnOkay()
	{
		// ARRANGE
		string paramX = "something";
		string responseX = "some response";
		_serviceMock.Setup(mock => mock.SomeMethodCall(paramX)).ReturnsAsync(responseX);
		
		// ACT
		var result = await _service.ProcessXXX(paramX);
	
		// ASSERT
		result.status.Should().NotBeNull();
		// ... assert whatever
	}
}

C# Async await with lambdas

If we want to use a method that’s marked as async inside a lambda expression, we have to split it in 2 steps:

  • task declaration
  • (async/await) task execution
// task declaration
var mapTask = animals.Select(Map).ToList();
// task execution
var animalsMapped = (await Task.WhenAll(mapTask)).ToList();

// mapping method
private async Task<Animal> Map(Animal animal)
{
	// ... do whatever mapping is needed
}

Bash scripts for port-forwards

The following is an example of the .sh scripts I use to forward and debug pods or features.

#!/bin/bash
# to use: sh portforward_microservice_xxx.sh env-dev | env-pre | env-pro
# it accepts additional params such as no-connectors to ignore some port forwards
# 	no-connectors - ignores forwards to XXX
args=("$@")
echo "INFO: using namespace ${args[0]}"

# only needed if we have several clusters for each env
if [ $1 == "env-pre" ]; then
	kubectl config use-context context-for-pre
elif [ $1 == "env-pro" ]; then
	kubectl config use-context context-for-pro
else	
	# default value - always DEV
	kubectl config use-context context-for-dev
fi

# add here new variables or cases to omit
no_connectors=false
for arg in "$@"; do
	case $arg in
		no-connectors)
			no_connectors=true
			shift
			;;	
		*)
			shift
			;;
	esac
done

if [ "$no_connectors" = false ]; then
	kubectl port-forward -n ${args[0]} svc/connector1 9210:9210 &
	kubectl port-forward -n ${args[0]} svc/connector2 8000:8000 &
else
	echo "INFO: ignoring connectors"
fi

# common pods we always need to call
kubectl port-forward -n ${args[0]} svc/service1 5050 &
kubectl port-forward -n ${args[0]} svc/service2 5060

EF Core Global Filters

(working code inside this project)

Let’s set a case where we have the following User class where we want to soft delete it, as we want to keep deleted records.

public class User
{
	public int Id { get; set; }
	public string Name { get; set; }
	public bool Active { get; set; }
}

In many cases we don’t care about “deleted” records so most times we will filter out deleted records like this

// DON'T DO THIS
public async Task<List<User>> GetUsers()
{
	return await _context.Users.Where(user => user.Active).ToList();
}

Instead of always doing this, which is too verbose, we may use Global Query Filters. This way we apply the filter globally.

public class ApDbContext : DbContext
{
	// ... more code
	
	protected override void OnModelCreating(ModelBuilder modelBuilder)
	{
		modelBuilder.Entity<User>().HasQueryFilter(user => user.Active);
	}
}

From now on, everytime we need to retrieve something from the User table, it will automatically filter out the deleted records.

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Testing. Code example for c#

The following are code examples to test several scenarios.

(check this project to see more testing code examples)

Test a controller

  • GivenCorrectDate_WhenGetAvailability_ThenAssertCorrectReturnValue asserts a controller returns 200 when everything goes right
  • GivenWrongDate_WhenGetAvailability_ThenAssert400ReturnValue assert a controller returns 400 with specific error message
  • GivenServiceThrowsException_WhenReserveSlot_ThenAssertExceptionCaught assert method throws an exception, but it is correctly caught
public class SlotsControllerTest
{
	// class we're testing
	private SlotsController _controller;

	private Mock<ISlotsService> _slotsServiceMock;
	
	private Mock<IOptions<CoreConfig>> _iOptConfigMock;
	private Mock<CoreConfig> _configMock;
	
	[SetUp]
	public void SetUp()
	{
		_configMock = new Mock<CoreConfig>();
		_iOptConfigMock = new Mock<IOptions<CoreConfig>>();
		_iOptConfigMock.Setup(iOpt => iOpt.Value).Returns(_configMock);
		
		_slotsServiceMock = new Mock<ISlotsService>();
		_controller = new SlotsController(_slotsServiceMock.Object, _iOptConfigMock.Object);
	}

[Test]
public async Task GivenWrongDate_WhenGetAvailability_ThenAssert400ReturnValue()
{
	// given
	string date = "";
	string errorMessage = "oh no! something went wrong!";
	
	var errorMessages = new ErrorMessages
	{
		GeneralErrorMessage = errorMessage
	};
	
	_configMock.Setup(conf => conf.GeneralErrorMessage).Returns(errorMessage);
	
	// when
	var result = await _controller.GetAvailability(date) as BadRequestObjectResult;
	
	// then
	result.Should().NotBeNull();
	result.StatusCode.Should().Be(400);
	result.Value.ToString().Should().Contain(errorMessage);
}

[Test]
public async Task GivenCorrectDate_WhenGetAvailability_ThenAssertCorrectReturnValue()
{
	// given
	string date = "20241012";
	var parsedDate = new DateOnly(2024, 10, 12);
	
	string dateFormat = "yyyyMMdd";
	_configMock.Setup(conf => conf.InputDateFormat).Returns(dateFormat);
	
	var dto = new WeekAvailabilityResponse();
	_slotsServiceMock.Setup(service => service.GetWeekSlotsAsync(parsedDate)).ReturnsAsync(dto);
	
	// when
	var result = await _controller.GetAvailability(date) as OkObjectResult;
	
	// then
	result.Should().NotBeNull();
	result.StatusCode.Should().Be(200);
	result.Value.Should().Be(dto);
}

[Test]
public async Task GivenServiceThrowsException_WhenReserveSlot_ThenAssertExceptionCaught()
{
	// given
	var request = new ReserveSlotRequest();

	string errorMessage = "error when throw exception";
	var errorMessages = new ErrorMessages
	{
		GeneralErrorMessage = errorMessage
	};
	
	_configMock.Setup(conf => conf.GeneralErrorMessage).Returns(errorMessage);
	_slotsServiceMock.Setup(service => service.ReserveSlotsAsync(parsedDate)).ThrowAsync(new HttpRequestException(errorMessage));

	// when
	var result = await _controller.ReserveSlot(request) as BadRequestObjectResult
	
	// then
	result.Should().NotBeNull();
	result.StatusCode.Should().Be(400);
	result.Value.ToString().Should().Contain(errorMessage);
}

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Code documentation in C#

Para documentar metodos en .NET es comun utiliar comentarios XML, mediante los cuales se puede generar documentacion externa usando herramientas como DocFX o Sandcastle.
Esto permite que tu API o biblioteca tenga una descripcion completa de cada método.

Ejemplo de comentario

public class ProductsController : ControllerBase
{
	/// <summary>
	/// Get a specific product by its ID.
	/// </summary>
	/// <param name="id">The ID from the product to retrieve</param>
	/// <returns>Returns the product if it's found. Otherwise it returns HTTP 404.</return>
	/// <response code="200">If the product is found.</response>
	/// <response code="404">If the product is not found.</response>
	[HttpGet("{id}")]
	public IActionResult GetProductById(int id)
	{
		var product = // get product from a service
		if(product is null)
		{
			return NotFound();
		}
		
		return Ok(product);
	}
}

Basic health checks

For many apps, a basic health probe configuration that reports the app’s availability to process request is sufficient to discover the status of the app

At Startup.cs we add the following

public void ConfigureServices(IServiceCollection services)
{
	// ... other configuration
	services.AddScoped<IUserService, UserService>();

	// add health checks
	services.AddHealthChecks();
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
	// ... other configuration

	// map health checks to an specific endpoint
	app.UseHealthChecks("/beat");
}

This endpoint will now be available at the service’s root. If this publish f.e. at port 5000, we can now call the following endpoint

http://localhost:5000/beat

// response
status 200, Healthy

The problem with this basic check is that if something fails inside the constructor of a controller or a service, this still returns status 200, Healthy.

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Herencia vs composicion

Ambas son dos maneras de reutilizar código para crear nuevas clases

Herencia

Permite que una subclase herede propiedades y métodos de su superclase o clase base. Facilita la reutilización de código y creación de relaciones jerárquicas entre clases.

Sin embargo puede llevar a estructuras de clases rígidas y complejas, y a problemas de acoplamiento.

Composición

En lugar de heredad de una clase base, la clase se “compone” de otras clases incluyendo instancias de otras clases como campos.

Esto promueve un diseño más modular y flexible ya que permite cambiar el comportamiento en tiempo de ejecución.

Depende del problema específico pero la composición suele ser preferida por su flexibilidad y capacidad para evitar problemas comunes de herencia.

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SOLID Principles

These principles establish practices that helps maintain and extend software as it grows.

S - single responsibility
O - open/closed
L - liskov substitution
I - interface segregation
D - dependency inversion

Single responsibility

A class should have only one job - it should have only one reason to change

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