LINQ Basics (Where, Select, OrderBy, FirstOrDefault) Masterclass

⚡ C# 12 & .NET 8 🟢 Chapter 23 of 35 📂 Phase 8: LINQ & Query Pipelines 📅 2026 Edition

📌 Covered in this chapter: LINQ Overview · Query vs Method Syntax · Where Filtering · Select Projection · OrderBy Sorting · FirstOrDefault · Aggregates (Sum, Avg, Min, Max)

Welcome to Phase 8 (Chapter 23): C# LINQ Basics (Language Integrated Query) Masterclass! LINQ integrates query capabilities directly into the C# language syntax. In this lesson, we cover query syntax vs method syntax, filtering (Where), projection (Select), sorting (OrderBy, ThenBy), element operators (First, FirstOrDefault, Single), and aggregate operators (Count, Sum, Average, Min, Max, Any, All).

1Method Syntax vs Query Syntax

C# — LINQ Method vs Query Syntax ▶ Run in Compiler

List<int> numbers = new() { 10, 15, 20, 25, 30 };

// 1. Method Syntax (Fluent API using Lambdas — Recommended)
var evenDoubledMethod = numbers
    .Where(number => number % 2 == 0)
    .Select(number => number * 2);

Console.WriteLine("Method Syntax Result:");
foreach (int num in evenDoubledMethod) Console.WriteLine(num);

// 2. Query Syntax (SQL-like syntax)
var evenDoubledQuery = from number in numbers
                       where number % 2 == 0
                       select number * 2;

2LINQ Aggregates & Element Operators

C# — LINQ Operators Example ▶ Run in Compiler

List<int> scores = new() { 85, 92, 78, 95, 60 };

Console.WriteLine($"Count: {scores.Count()}");
Console.WriteLine($"Sum: {scores.Sum()}");
Console.WriteLine($"Average: {scores.Average():F2}");
Console.WriteLine($"Max: {scores.Max()}, Min: {scores.Min()}");

bool hasTopScorer = scores.Any(s => s >= 90);
Console.WriteLine($"Has 90+ score: {hasTopScorer}");

int firstPass = scores.FirstOrDefault(s => s >= 80);
Console.WriteLine($"First score >= 80: {firstPass}");

3Technical FAQs

Q1: What is the difference between First() and FirstOrDefault()?

First() throws an InvalidOperationException if no matching element is found. FirstOrDefault() returns the type's default value (e.g., 0 or null) safely without throwing an exception.