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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ASP.NET Core offers several cache types. I’m going to explore here IMemoryCache which stores data in the memory of the web server. It’s simple but not suitable for distributed scenarios.

first of all we need to register the services

builder.Services.AddMemoryCache();

here’s how you can use it

public service(IMemoryCache cache, AppDbContext context)
{
	public Person GetPerson(string id)
	{
		if(!cache.TryGetValue(id, out Person person))
		{
			person = context.Persons.Find(id);

			var cacheEntryOptions = new MemoryCacheEntryOptions()
				.SetAbsoluteExpiration(TimeSpan.FromMinutes(10))
				.SetSlidingExpiration(TimeSpan.FromMinutes(2));

			cache.Set(id, person, cacheEntryOptions);
		}

		return person;
	}
}

Reference(s)

https://www.milanjovanovic.tech/blog/caching-in-aspnetcore-improving-application-performance

Dependency injection is native-available in .NET Core

DI implementation

interface we want to inject

public interface IDateTime
{
	DateTime Now { get; }
}

interface’s implementation

public class SystemDateTime : IDateTime
{
	public DateTime Now
	{
		get { return DateTime.Now; }
	}
}

service we inject into

public class HomeController : Controller
{
	private readonly IDateTime _dateTime;

	public HomeController(IDateTime dateTime)
	{
		_dateTime = dateTime;
	}

	public IActionResult Index()
	{
		var serverTime = _dateTime.Now;
		return Ok(serverTime);
	}
}

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Anonymous types provide an easy way to encapsulate different properties in a single object. Unlike properties in a class, the properties of anonymous type objects are read-only.

Declare and use anon type objects

declaration

var loginCredentials = new { Username = "suresh", Password = "******" };
Console.WriteLine($"Username {loginCredentials.Username.ToString()}");
Console.WriteLine($"Password {loginCredentials.Password.ToString()}");

After assigning values to the Username and Password properties, they cannot be altered *(they’re readonly).

Anon objects in LINQ

Usually, anon data types are used in the select clause to return a specific subset of properties for each object in the collection.

we have the employee class

public class Employee
{
	public int ID { get; set; }
	public string Name { get; set; }
	public int Age { get; set; }
	public string Address { get; set; }
}

List<Employee> employees = // whatever ...
// we convert an Employee into an anon object type with a subset of properties
var employeeDetails = from emp in employees
	select new { Id = emp.ID, Name = emp.Name };

Reference(s)

https://www.syncfusion.com/blogs/post/understanding-csharp-anonymous-types

List vs ArrayList

Don’t use ArrayList. Use List<T> instead. ArrayList comes from times when C# didn’t have generics and it’s not the same ArrayList we have in Java.

DON’T

ArrayList array = new ArrayList();
array.Add(1);
array.Add("Pony"); // Later error at runtime if you try to operate with numbers.

do

List<int> list = [];
list.Add(1);
list.Add("Pony"); // Compilation error. 

retrieve data

List<string> list = [ "yes", "no"];
var firstItem = list[0];

Tuples

Tuples help us manipulate data sets easily without having to define a new class with custom properties.

One of its benefits is that they can be used as method params and return types.

// simple tuple
(int, string) employee = (23, "Yohannes");
Console.WriteLine($"{employee.Item2} is {employee.Item1} years old");

// tuple with named parameters
(int Age, string Name) employee2 = (29, "Ramon");
Console.WriteLine($"{employee2.Name} is {employee2.Age} years old");

// nested tuples
var employees = ((23, "Yohannes"), (29, "Ramon"));
Console.WriteLine(employees.Item1); // (23, "Yohannes")
Console.WriteLine(employees.Item1.Item1); // 23

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A concise syntax to declare constructors whose params are available anywhere in the body.

Primary constructors is an easier way to create a constructor for your class or struct, by eliminating the need for explicit declarations of private fields and bodies that only assign param values.

They are great when you just need to do simple initialization of fields and for dependency injection.

Code example without primary constructors

public class BookDefault
{
	public int Id { get; }
	public string Title { get; }
	public int Pages { get; set; }
	private readonly List<decimal> ratings = new List<decimal>();
	public decimal? AverageRating => ratings.Any() ? ratings.Average() : 0m;

	public BookDefault(int id, string title, IEnumerable<decimal>? rating = null)
	{
		ArgumentException.ThrowIfNullOrEmpty(id);
		ArgumentException.ThrowIfNullOrEmpty(title);
		
		Id = id;
		Title = title;
		if(rating?.Any() == true)
		{
			ratings.AddRange(rating);
		}
	}
}

Code example using primary constructors

public class Book(int id, string title, IEnumerable<decimal> ratings)
{
	public int Id => id;
	public string Title => title.Trim();
	public int Pages { get; set; }
	public decimal AverageRating => ratings.Any() ? ratings.Average() : 0m;
}

another example

public class Person(string firstName, string lastName)
{
	public string FirstName { get; } = firstName;
	public string LastName { get; } = lastName;
}

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Collection expressions try to unify all syntaxes for initializing different collections. With them you can use the same syntax to express collections in a consistent way.

They replace all of this:

// all these versions are equivalent - the compiler generates identical code for each version
var numbers1 = new int[3] {1, 2, 3};
var numbers2 = new int[] {1, 2, 3};
var numbers3 = new[] {1, 2, 3};
int[] numbers4 = {1, 2, 3};

Using the new collection expressions (they cannot be used with var. You must declare the type)

// create an array
int[] intArray = [1, 2, 3, 4, 5];
// create empty array
int[] emptyArray = [];
// create a list
List<char> charList = ['D', 'a', 'v', 'i', 'd'];
// create a 2D list
List<int> int2dList = [[1, 2, 3], [4, 5, 6,], [7, 8, 9]];

how to flatten collections

int[] row0 = [1, 2, 3];
int[] row1 = [4, 5, 6];
int[] flattenCollection = [.. row0, 100, .. row1];
foreach(element in flattenCollection)
{
	Console.Write($"{element}, ");
}
// 1, 2, 3, 100, 4, 5, 6,

Reference(s)

https://devblogs.microsoft.com/dotnet/refactor-your-code-with-collection-expressions/
https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-12#collection-expressions

Reference types vs value types

Reference types are allocated on the heap and garbage-collected, whereas value types are allocated on the stack so their (de)allocation are generally cheaper.

Arrays of reference types contain just references to instances of the reference type residing on the heap. Value type arrays hold the actual instance of the value type. Value type arrays are much cheaper than reference type arrays.

Value types get boxed when cast to a reference type or one of the interfaces they implement. They get unboxed when cast back to the value type. Boxes are objects that are allocated on the heap and are garbage-collected. Too much boxing and unboxing can have a negative impact.
In contrast, no such boxing occurs for reference types.

Reference type assignments copy the reference, whereas value type assignments copy the entire value. Assignments of large reference types are cheaper than assignments of large value types.

Reference types are passed by reference, whereas value types are passed by value. Changes to an instance of a reference type affect all references pointing to the instance. Value type instances are copied when they’re passed. When an instance of a value type is changed, it doesn’t affect any of its copies.

You can’t have a null value type. “null” only means a memory address reference is missing.

Class

Class is a reference type. When you compare reference types, this comparison checks if the compared objects are the same object (heap location).

You can specify access modifier if required (private, public, protected, internal).

class declaration

class Person
{
	public string Name {get; set;}
	public int Age {get; set;}
}

create an object

Person person = new Person();
person.Age = 30;
person.Name = "Mario";
Console.WriteLine(person.Name + " " + person.Age); // Mario 30

create another object using the first object we created

Person person2 = person; 
person2.Age = 29;
Console.WriteLine(person.Name + " " + person.Age); // Mario 29
Console.WriteLine(person2.Name + " " + person2.Age); // Mario 29

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This details various ways that you can interact with the code and data running inside your pod.

Access a Pod via Network

If you want access to a specific pod, even if it’s not serving traffic on the internet. To achieve this, Kubernetes has support built into it.

kubectl port-forward <pod-name> <localport>:<podport>
kubectl port-forward istio 5015:80

A secure tunnel is created from your local machine, though the K8s master, to the instance of the Pod running on one of the worker nodes.

Getting More Info with Logs

When you need to debug.

# downloads the current logs from the running instance
kubectl logs kuard

# continuously streams logs
kubectl logs -f kuard

# get logs from a previous instance of the container. Useful if your containers are continuously restarting at startup. 
kubectl logs kuard --previous

• -c if you have multiple containers in your Pod, you can choose the one to view

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RDF (Resource Description Framework) - modelo de datos para representar datos como grafos (datos interconectados). Está dirigido y etiquetado para representar la información en la web.

SPARQL - query language estandarizado para consulta de grafos RDF.

Cuando trabajan ambos juntos, RDF y SPARQL te permiten construir aplicaciones de grafos.

What’s an RDF Graph?

This just means data represented using the RDF data model. This is what an example of such graph may look like

An RDF grahp is a directed graph consisting of nodes which are connected together by crearly labelled relationships with directionality. These relationships are known as edges. These edges connect one node to another.

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It’s possible to import directly from JSON to Excel. This allows us to easily filter by some JSON fields or execute Excel queries on top of our JSON data.

I have a json file with hundreds of items following this structure.

{
	"_id": "63371b0027484f4f9f00587d",
	"guid": "ab4059e7-6441-4593-8272-42c53e4742d2",
	"isActive": true,
	"balance": "$2,120.18"
}

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