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Querying With LINQ

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All About LINQ

3:20 with Carling Kirk

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

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    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. 0:28
    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 0:42
    then why would we use it? 0:45
    Why reinvent the wheel? 0:47
    Well, it makes it way easier and 0:48
    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. 1:05
    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? 1:38
    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 2:11
    a for each loop. 2:15
    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 2:33
    IEnumerable or, more generally, anything that we can use LINQ with. 2:38
    There are two flavors of syntax we can use when writing LINQ queries, 2:44
    query syntax and method syntax. 2:48
    Every developer has their preference, but there are some 2:51
    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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