3.LINQ & Lambda Expressions - aniketmulmule/web_Project GitHub Wiki

Here’s an in-depth guide to LINQ and Lambda Expressions in C#, tailored for someone with 8+ years of experience, along with how to explain them in interviews (with real-world and advanced insights).

LINQ (Language Integrated Query) is a powerful feature that brings querying capabilities into C# using a declarative syntax.

You can query:

• Collections (IEnumerable)

• Databases (IQueryable)

• XML

• Objects

• Remote services (via LINQ providers like Entity Framework, LINQ to SQL)

// Query syntax (like SQL)
var result = from p in products
             where p.Price > 1000
             select p;
// Method (fluent) syntax with lambda
var result = products.Where(p => p.Price > 1000);

A Lambda Expression is an anonymous function you use with delegates, Func<>, Action<>, or LINQ.

// (input) => expression
x => x * x  // square
(p1, p2) => p1 + p2  // sum

They are heavily used in:

• LINQ

• Events

• Functional-style programming

• Async callbacks

• Custom sorting/filtering

Would you like:

• 📄 A PDF cheat sheet of this content?

• 💡 A project idea to practice advanced LINQ?

• 🧪 Or a set of mock interview questions to simulate senior-level interviews?

Let me know!

LINQ (Language Integrated Query) is a powerful feature that brings querying capabilities into C# using a declarative syntax.

You can query:

• Collections (IEnumerable)
• Databases (IQueryable)
• XML
• Objects
• Remote services (via LINQ providers like Entity Framework, LINQ to SQL)

// Query syntax (like SQL)
var result = from p in products
             where p.Price > 1000
             select p;

// Method (fluent) syntax with lambda
var result = products.Where(p => p.Price > 1000);

A Lambda Expression is an anonymous function you use with delegates, Func<>, Action<>, or LINQ.

// (input) => expression
x => x * x  // square
(p1, p2) => p1 + p2  // sum

They are heavily used in:

• LINQ
• Events
• Functional-style programming
• Async callbacks
• Custom sorting/filtering

var expensiveProducts = products
    .Where(p => p.Price > 1000)
    .OrderByDescending(p => p.Price)
    .Select(p => new { p.Name, p.Price });

var grouped = products
    .GroupBy(p => p.Category)
    .Select(g => new { Category = g.Key, Count = g.Count() });

var result = customers.Join(orders,
    c => c.Id,
    o => o.CustomerId,
    (c, o) => new { c.Name, o.OrderId });

string sentence = words.Aggregate((acc, word) => acc + " " + word);

Used for 1-to-many relationships, like getting all orders from customers.

var allOrders = customers.SelectMany(c => c.Orders);

var lookup = products.ToLookup(p => p.Category);

var totalLength = strings.Aggregate(0, (sum, s) => sum + s.Length);

"LINQ gives a functional, declarative way to work with data. I use it extensively for in-memory filtering, projection, grouping, and even to chain business logic pipelines."

"In backend services, I’ve used LINQ with EF Core for query translation to SQL, optimizing performance with AsNoTracking, deferred execution, and projection to DTOs."

"Lambda expressions make code concise and expressive. I use them in LINQ, event subscriptions, and even in async workflows. They also help build reusable components like filters and mapping strategies."

• Deferred Execution: Avoid bugs by materializing (e.g., ToList()).
• Performance: Avoid loading large datasets in memory.
• Select N+1: Understand EF Core lazy loading.
• Chained Queries: Avoid multiple enumerations.
• Using All vs Any: Know the difference for filtering logic.

Would you like:

• 📄 A PDF cheat sheet of this content?
• 💡 A project idea to practice advanced LINQ?
• 🧪 Or a set of mock interview questions to simulate senior-level interviews?

Let me know!