LINQ with custom objects in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is LINQ in C#?

LINQ (Language Integrated Query) is a feature in C# that allows you to query collections like arrays or lists using a readable, SQL-like syntax directly in the code.

beginner

How do you define a custom object to use with LINQ?

A custom object is a class you create with properties. For example, a <code>Person</code> class with <code>Name</code> and <code>Age</code> properties can be used in LINQ queries.

beginner

What does this LINQ query do?<br>

var adults = people.Where(p => p.Age >= 18);

This query selects all people whose Age is 18 or older. It filters the list to only adults.

beginner

How can you select only the names from a list of custom objects using LINQ?

Use the Select method to pick the Name property: var names = people.Select(p => p.Name); This creates a list of names.

beginner

What is the difference between Where and Select in LINQ?

Where filters items based on a condition (like a sieve). Select transforms each item into something new (like picking a part of each item).

What does this LINQ query return?<br>

var result = people.Where(p => p.Age < 30);

A All people younger than 30

B All people older than 30

C All people exactly 30 years old

D All people regardless of age

The Where method filters the list to include only people with Age < 30.

Which LINQ method would you use to get only the names from a list of Person objects?

A Where

B GroupBy

C OrderBy

D Select

Select is used to transform each object into a specific property, like Name.

Given a list of custom objects, how do you filter items with LINQ?

A Use Where

B Use Select

C Use OrderBy

D Use ToList

Where filters items based on a condition.

What type of object does a LINQ query like people.Where(...) return?

A A single object

B A filtered collection

C An integer count

D A boolean value

LINQ Where returns a collection of items that match the condition.

Which keyword is used in LINQ lambda expressions to represent each item?

A item

B var

C p

D =>

In p => p.Age > 18, p represents each item in the collection.

Explain how to use LINQ to filter a list of custom objects based on a property.

Think about how you pick only some items from a list.

Describe the difference between the LINQ methods Where and Select when working with custom objects.

One chooses items, the other picks parts of items.