LINQ Refresher
Owen Evans,
Developer, Xero
Blogger, http://bgeek.net
Thursday, February 19, 2009

LINQ
Thursday, February 19, 2009

Language INtegrated Query
Thursday, February 19, 2009

SELECT
lets start at the beginning
Thursday, February 19, 2009

SELECT
Structured Separated LINQ
Query Language (SQL)
Thursday, February 19, 2009

Back Up
Anonymous Types
Thursday, February 19, 2009

Anonymous Types
Allow you to create a new type without defining a class
two methods of declaration
explicit new{ObjectName=object.Name}
implicit new{object.Description}
new{object.Name} is the same as
new{Name=object.Name}
Thursday, February 19, 2009

Revisiting Select
What does this give us?
Thursday, February 19, 2009

Answer?
An IEnumerable<T> Also See IQueriable<T>
and
IOrderedEnumerable<T>
Thursday, February 19, 2009

Order
get in line
Thursday, February 19, 2009

Order By
Thursday, February 19, 2009

Join
Thursday, February 19, 2009

Let
Thursday, February 19, 2009

LINQ as Extension Methods
Thursday, February 19, 2009

Late Evaluation
LINQ queries are not evaluated until you need the
results (foreach, count, etc.)
Allows for optimisation and building up of the query
over time
Can produce unexpected results if you don’t know
what to expect
Thursday, February 19, 2009

Late eval can hide errors
Thursday, February 19, 2009

Things to remember about
LINQ
From Comes First (for intellisense purposes)
can be written using extension methods (helps in
exploring what is possible)
Can project to new lists of objects or anonymous
objects
Beware hard to follow LINQ
Late Evaluation: things can change, beware holding
onto the IEnumerable for too long.
Thursday, February 19, 2009

All in one place
Thursday, February 19, 2009

References
MSDN: http://msdn.microsoft.com/en-us/library/
bb308959.aspx
LINQ over REST (Astoria): http://msdn.microsoft.com/
en-us/library/bb308959.aspx
Many many ORM’s now providing LINQ support:
Lightspeed, NHibernate, LINQ to Entities (LINQ to SQL
too but abandoned)
Thursday, February 19, 2009

A Few More References
(thanks to Simon Green)
http://www.linqpad.net/
Great for learning LINQ, includes heaps of samples
Works outside of Visual Studio
See the generated SQL or lambda
http://www.albahari.com/nutshell/linqbridge.aspx
Use LINQ to Objects in projects targeting .NET 2.0
Thursday, February 19, 2009

FIN
Thursday, February 19, 2009