C# Tutorial 10.1 :Basic LINQ queries

  LINQ is a powerful feature in C# that allows you to query data from various sources using a SQL-like syntax.

Step 1: Understand LINQ Basics

Before diving into LINQ queries, it's essential to understand the basic concepts of LINQ:

• IEnumerable<T>: LINQ works with collections that implement the IEnumerable<T> interface. Most of the standard collections in C# like arrays, lists, and dictionaries implement this interface.

• Lambda Expressions: LINQ uses lambda expressions to define anonymous functions. Lambda expressions are concise ways to represent methods without explicitly defining a separate method.

• Query Expressions: LINQ queries are written using a SQL-like syntax, referred to as query expressions.

Step 2: Set Up Your Project

Create a new C# Console Application in Visual Studio or your preferred IDE.

Step 3: Import Necessary Libraries

Make sure to include the following using directive at the top of your C# file to use LINQ:

using System.Linq;

Step 4: Create a Sample Data Source

For the purpose of this tutorial, let's create a simple class and a list of objects. Consider the following class:

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

Now, create a list of Person objects in the Main method:

List<Person> people = new List<Person>
{
    new Person { Name = "Alice", Age = 25 },
    new Person { Name = "Bob", Age = 30 },
    new Person { Name = "Charlie", Age = 22 },
    new Person { Name = "David", Age = 35 }
};

Step 5: Basic LINQ Queries

Now, let's explore some basic LINQ queries:

Query 1: Filtering

// Get people who are older than 25
var result = from person in people
             where person.Age > 25
             select person;
foreach (var person in result)
{
    Console.WriteLine($"{person.Name} is {person.Age} years old.");
}

Query 2: Projection

// Select only the names of people
var names = from person in people
            select person.Name;
foreach (var name in names)
{
    Console.WriteLine($"Name: {name}");
}

Query 3: Ordering

// Order people by age in ascending order
var orderedPeople = from person in people
                    orderby person.Age
                    select person;
foreach (var person in orderedPeople)
{
    Console.WriteLine($"{person.Name} is {person.Age} years old.");
}

Query 4: Aggregation

// Calculate the average age of people
var averageAge = people.Average(person => person.Age);
Console.WriteLine($"Average Age: {averageAge}");

Step 6: Run and Experiment

Run your program and see the results of each query. Feel free to modify the queries and experiment with different LINQ operators.

This is a basic introduction to LINQ in C#, and there's much more you can do with LINQ, including joining, grouping, and more advanced operations. Explore the official Microsoft documentation for LINQ for a comprehensive understanding: LINQ (Language-Integrated Query).