Introduction to LINQ in C#

LINQ (Language Integrated Query) is one of the most powerful and elegant features in C#. It allows you to query collections, databases, XML, and more — using a SQL-like syntax directly in C#.

What is LINQ?

LINQ stands for Language Integrated Query. It provides a consistent, readable, and type-safe way to query different types of data sources such as:

Arrays and Lists
XML Documents
Databases (via LINQ to SQL or Entity Framework)
JSON or Web APIs

Benefits of LINQ

Benefit	Description
Unified Query Style	Same syntax for querying different data sources
Type Safety	Errors caught at compile-time, not runtime
Readability	Code is cleaner and closer to English or SQL
Productivity	Reduces the amount of boilerplate looping and filtering code

LINQ Query Syntax vs Method Syntax

C# offers two ways to write LINQ queries:

1. Query Syntax (SQL-like style)

var result = from n in numbers
             where n > 5
             orderby n
             select n;

2. Method Syntax (Lambda-based)

var result = numbers.Where(n => n > 5).OrderBy(n => n);

Both produce the same result — it’s just a matter of preference!

LINQ with Collections – Example

using System;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List<string> names = new List<string> { "Alice", "Bob", "Eve", "Charlie" };

        // LINQ query to filter names starting with 'C'
        var result = from name in names
                     where name.StartsWith("C")
                     select name;

        foreach (var name in result)
        {
            Console.WriteLine(name);  // Output: Charlie
        }
    }
}

Common LINQ Operators

Operator	Description
`Where`	Filters a sequence based on condition
`Select`	Projects each element into a new form
`OrderBy`	Sorts elements in ascending order
`OrderByDescending`	Sorts in descending order
`GroupBy`	Groups elements
`Join`	Joins two sequences based on keys
`Distinct`	Removes duplicates
`Take`, `Skip`	Limits and skips elements
`Any`, `All`	Checks for conditions

LINQ Example with Integers

int[] numbers = { 1, 2, 3, 4, 5, 6 };

var evenNumbers = numbers.Where(n => n % 2 == 0);

foreach (int num in evenNumbers)
{
    Console.WriteLine(num);  // Output: 2, 4, 6
}

LINQ to Objects vs LINQ to SQL

Feature	LINQ to Objects	LINQ to SQL/EF
Source	In-memory collections	Database tables
Execution	Immediate or deferred	Translates to SQL queries
Libraries Used	`System.Linq`	`System.Data.Linq`, Entity Framework

Summary

Topic	Description
LINQ Full Form	Language Integrated Query
Main Types	Query Syntax, Method Syntax
Works With	Arrays, Lists, XML, SQL, JSON
Key Benefits	Cleaner code, type-safe, reusable logic

Next Steps

Learn deferred execution and how LINQ works under the hood
Dive into LINQ to SQL or Entity Framework
Explore GroupBy, Join, and Aggregate functions

Updated 22-Apr-2025

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