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What is LINQ and how can we use it?
C# Basics Course on Treehouse
C# Objects Course on Treehouse
Collections
C# features that support LINQ:
- Anonymous Types
- Extension Methods
- Implicit Typing
- Lambda Expressions
- Object and Collection Initializers
Hi I'm Carling,
I'm a Treehouse teacher and a developer.
0:05
In this course,
I'm going to teach you all about LINQ.
0:09
LINQ is a powerful toolset
in the .NET Framework
0:12
that enables C# developers to query and
manipulate collections of objects.
0:15
LINQ stands for language integrated query.
0:20
LINQ was introduced in C# 3.0 to give
developers the querying power of
0:24
a database querying language like SQL.
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If you've used SQL, or S-Q-L,
LINQ will seem pretty familiar.
0:32
But if you haven't, no worries.
0:36
You can still learn to use
LINQ with this course.
0:39
LINQ doesn't really provide
much we couldn't do before, so
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then why would we use it?
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Why reinvent the wheel?
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Well, it makes it way easier and
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faster to write code that would otherwise
be verbose and complicated to read.
0:50
Before LINQ if we wanted to get
a subset of objects from a collection,
0:56
we would write a loop, compare each object
to see if it was the one we want and
1:00
then stick it into a new collection.
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It could end up being 20 lines long.
1:07
Now with LINQ,
we can do it with only one line of code.
1:10
And even better,
our code becomes more readable and
1:13
self-documenting because
the methods we'll use like Where or
1:17
OrderBy are more like writing
a sentence than actual code.
1:21
Along with LINQ came a lot of other new
language features to help support it.
1:26
We'll touch on all these along the way
as we learn to query with LINQ, but
1:30
you can find a list of them
in the teacher's notes.
1:34
So how do we use LINQ?
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We can use LINQ on collections
like arrays or lists.
1:40
If you haven't heard of a list or
a collection yet, you should check out
1:44
the teacher's notes for
more resources before diving into LINQ.
1:48
But more specifically we can use
LINQ with anything that implements
1:51
IEnumerable of T in
the system.collections.genericnamespace.
1:57
IEnumerable is an interface in the .NET
framework that, when implemented for
2:02
a type,
tells us that it has an enumerator.
2:07
That means that the objects in it can be
looped through like we do in a for or
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a for each loop.
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If all this sounds unfamiliar to you,
2:18
you should check out our course on C#
objects to learn about arrays and loops.
2:20
You can find a link in
the teacher's notes.
2:25
I'll be using the terms collections and
2:28
sequences interchangeably
throughout this course.
2:30
Just keep in mind that if I use either
term, it's really anything that implements
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IEnumerable or, more generally,
anything that we can use LINQ with.
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There are two flavors of syntax we
can use when writing LINQ queries,
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query syntax and method syntax.
2:48
Every developer has their preference,
but there are some
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things you can do with method syntax
that you can't do with query syntax.
2:54
We're going to start out by using query
syntax, but since you'll probably be
2:58
reading both in the future, we'll get
into using method syntax a little later.
3:03
Using method syntax requires getting into
those supporting language features I
3:08
mentioned earlier.
3:12
All right, my fingers are itching to code.
3:15
Let's open up Workspaces and
start playing with LINQ.
3:17
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