Hi I'm Carling, I'm a Treehouse teacher and a developer.

In this course, I'm going to teach you all about LINQ.

LINQ is a powerful toolset in the .NET Framework

that enables C# developers to query and manipulate collections of objects.

LINQ stands for language integrated query.

LINQ was introduced in C# 3.0 to give developers the querying power of

a database querying language like SQL.

If you've used SQL, or S-Q-L, LINQ will seem pretty familiar.

But if you haven't, no worries.

You can still learn to use LINQ with this course.

LINQ doesn't really provide much we couldn't do before, so

then why would we use it?

Why reinvent the wheel?

Well, it makes it way easier and

faster to write code that would otherwise be verbose and complicated to read.

Before LINQ if we wanted to get a subset of objects from a collection,

we would write a loop, compare each object to see if it was the one we want and

then stick it into a new collection.

It could end up being 20 lines long.

Now with LINQ, we can do it with only one line of code.

And even better, our code becomes more readable and

self-documenting because the methods we'll use like Where or

OrderBy are more like writing a sentence than actual code.

Along with LINQ came a lot of other new language features to help support it.

We'll touch on all these along the way as we learn to query with LINQ, but

you can find a list of them in the teacher's notes.

So how do we use LINQ?

We can use LINQ on collections like arrays or lists.

If you haven't heard of a list or a collection yet, you should check out

the teacher's notes for more resources before diving into LINQ.

But more specifically we can use LINQ with anything that implements

IEnumerable of T in the system.collections.genericnamespace.

IEnumerable is an interface in the .NET framework that, when implemented for

a type, tells us that it has an enumerator.

That means that the objects in it can be looped through like we do in a for or

a for each loop.

If all this sounds unfamiliar to you,

you should check out our course on C# objects to learn about arrays and loops.

You can find a link in the teacher's notes.

I'll be using the terms collections and

sequences interchangeably throughout this course.

Just keep in mind that if I use either term, it's really anything that implements

IEnumerable or, more generally, anything that we can use LINQ with.

There are two flavors of syntax we can use when writing LINQ queries,

query syntax and method syntax.

Every developer has their preference, but there are some

things you can do with method syntax that you can't do with query syntax.

We're going to start out by using query syntax, but since you'll probably be

reading both in the future, we'll get into using method syntax a little later.

Using method syntax requires getting into those supporting language features I

mentioned earlier.

All right, my fingers are itching to code.

Let's open up Workspaces and start playing with LINQ.