Litwin linq

Introduction to LINQ
Paul Litwin
Deep Training
paull@deeptraining.com
1

Agenda
What is LINQ?
Language Features Behind LINQ
LINQ Basics
LINQ to Objects
LINQ to SQL
Other LINQ providers

2

Paul Litwin
Developer
Focus: ASP.NET, ASP, VB, C#, SQL Server, …
MCSD
Microsoft MVP
Programming Manger with
Fred Hutchinson Cancer Research Center (Seattle)

Co-Founder and Senior Trainer
Deep Training
www.deeptraining.com

Conference Chair/Speaker
Chair, Microsoft ASP.NET Connections
Member INETA Speakers Bureau

Author
Author/co-author of a dozen books, including…
ASP.NET for Developers
Access Cookbook, 2nd edition
Access 2002 Desktop/Enterprise Dev Handbook
AppDev SQL Server 2005 Reporting Services Course

3

This Talk Brought to You By…
INETA
International .NET Users Association
Speaker Bureau

4

What is LINQ?
LINQ == Language Integrated Query
Additions to .NET languages that enable
language-based querying
LINQ Providers
LINQ to Objects – in memory-collections
LINQ to SQL – SQL Server databases
LINQ to XML – XML documents
LINQ to DataSets – data in a ADO.NET DataSet
LINQ to Entities – works with ADO.NET Entity
Framework
…

5

Language Features Behind LINQ
Automatic Properties
Object and Collection Initializers
Inferred and Anonymous Types
Extension Methods
Lambda Expressions

6

Automatic Properties – C# Only
Quick way to define property Not really
necessary for LINQ but nice
replace this

with this

private string _firstName;
private string _firstName;

public string firstName { get; set; }
public string firstName { get; set; }

public string firstName
public string firstName
{
{
get { return _firstName; }
get { return _firstName; }
set { _firstName = value; }
set { _firstName = value; }
}
}

7

Object Initializers – C#
Quick way to create an instance and set a
bunch of properties
replace this
Cust20 cust20 = new Cust20();
Cust20 cust20 = new Cust20();
cust20.firstName = "Groucho";
cust20.firstName = "Groucho";
cust20.lastName = "Marx";
cust20.lastName = "Marx";
cust20.birthDate = new DateTime(1890, 10, 2);
cust20.birthDate = new DateTime(1890, 10, 2);

with this
Cust35 cust35 = new Cust35 { firstName = "Jim",
Cust35 cust35 = new Cust35 { firstName = "Jim",
lastName = "Gaffigan", birthDate = new DateTime(1966, 7, 7) };
lastName = "Gaffigan", birthDate = new DateTime(1966, 7, 7) };
8

Object Initializers – VB
Quick way to create an instance and set a
bunch of properties
replace this
Dim cust20 As New Cust20()
Dim cust20 As New Cust20()
cust20.firstName = "Groucho"
cust20.firstName = "Groucho"
cust20.lastName = "Marx"
cust20.lastName = "Marx"
cust20.birthDate = New DateTime(1890, 10, 2)
cust20.birthDate = New DateTime(1890, 10, 2)

with this
Dim cust20 As New Cust20() With {.firstName = "Jim", _
Dim cust20 As New Cust20() With {.firstName = "Jim", _
.lastName = "Gaffigan", .birthDate = New DateTime(1966, 7, 7)}
.lastName = "Gaffigan", .birthDate = New DateTime(1966, 7, 7)}
9

Collection Initializers – C# Only
replace this
List<Cust20> pcTitans20 = new List<Cust20>();
List<Cust20> pcTitans20 = new List<Cust20>();
Cust20 steveJobs = new Cust20();
Cust20 steveJobs = new Cust20();
steveJobs.firstName = "Steve";
steveJobs.firstName = "Steve";
steveJobs.lastName = "Jobs";
steveJobs.lastName = "Jobs";
steveJobs.birthDate = new DateTime(1955, 2, 24);
steveJobs.birthDate = new DateTime(1955, 2, 24);
pcTitans20.Add(steveJobs);
pcTitans20.Add(steveJobs);
…
…

with this
List<Cust20> pcTitans35 = new List<Cust35>
List<Cust20> pcTitans35 = new List<Cust35>
{
{
new Cust35{firstName="Steve",lastName="Jobs",
new Cust35{firstName="Steve",lastName="Jobs",
birthDate=new DateTime(1955,2,24)},
birthDate=new DateTime(1955,2,24)},
…
…
}
}

10

Type Inference
Have compiler infer type from usage
C#

var serialNumber1 = 123456;
var serialNumber2 = "789";

// inferred as int
// inferred as string

VB

Dim serialNumber1 = 123456
Dim serialNumber2 = "789"

' inferred as int
' inferred as string

11

Anonymous Types
Allow you create an instance of an unnamed (i.e., anonymous) class that is
defined in line
C#
var myHouse = new {color = "green", address = "100 Elm"}

VB
Dim myHouse = New With {.color = "green", _
.address = "100 Elm"}

12

Extension Methods – C#
Allow you to add a custom method to an
existing type
public static class ScottGuExtensions
{
public static bool IsValidEmailAddress (this string s)
{
Regex regex = new
Regex(@"^[w-.]+@([w-]+.)+[w-]{2,4}$");
return regex.IsMatch(s);
}
}
13

Extension Methods – VB
Allow you to add a custom method to an
existing type
Imports System.Runtime.CompilerServices
Imports System.Text.RegularExpressions
Public Module ScottGuExtensions
Public
ScottGuExtensions
<Extension()> _
Public Function IsValidEmailAddess(ByVal s As String) _
As Boolean
Dim regex As Regex = _
As
New Regex("^[w-.]+@([w-]+.)+[w-]{2,4}$")
Return regex.IsMatch(s)
End Function
End Module

14

Basic LINQ Examples
Comedians = new List<String> { "Groucho Marx", "Eric Idle", … }
var results = from c in Comedians
where c.Contains("Marx")
select c;
orderby c
select c;

LINQ2Objects.aspx – C#
LINQ2ObjectsVB.aspx – VB
15

Query Basics – C#
Query expression consists of set of clauses written
in a declarative syntax similar to SQL or XQuery
Query must
begin with from clause, and
end with select or group clause

Between 1st from clause and last select/group
clause, it can contain one or more of following
clauses
where
orderby
join
let
from
into

16

Query Basics – VB
Query expression consists of set of clauses written
in a declarative syntax similar to SQL or XQuery
Query must
begin with From or Aggregate clause

After From/Aggregate clause, you may include any
of following clauses
Select
Where
Order By
Join
Group By
Aggregate
Let

Distinct
Take
Take While
Skip
Skip While
Into
17

Contrasting Query Keywords
C# LINQ

VB LINQ

ANSI SQL

from

From

FROM

select

Select

SELECT

where

Where

WHERE

orderby

Order By

ORDER BY

join

Join

JOIN

group

Group By

GROUP BY

Distinct()

Distinct

DISTINCT

into

Into

INTO

let

Let

AS

Count(), Sum(),…

Aggregate

COUNT, SUM,… w/ no group

Skip()
SkipWhile()

Skip
Skip While

n/a

Take()
TakeWhile()

Take
Take While

n/a

18

LINQ Basics
There are two ways to write LINQ queries
Query syntax
The previous examples used this syntax

Method syntax
This syntax uses Lambda expressions

19

Anonymous Methods Review
C# 2.0 introduced anonymous methods
C# 1.0
btn.Click += new EventHandler(btn_Click):
btn.Click += new EventHandler(btn_Click):
void btn_Click(object sender, EventArgs e)
void btn_Click(object sender, EventArgs e)
{
{
lblResult.txt = "Hello world";
lblResult.txt = "Hello world";
}
}

C 2.0
btn.Click += delegate(object sender, EventArgs e)
{
{
lblResult.Text = "Hello World";
lblResult.Text = "Hello World";
}
}
20

Lambda Expressions
Lambda expression take the C# 2.0
anonymous method one step further
C 2.0
{
{
lblResult.Text = "Hello!";
lblResult.Text = "Hello!";
}
}

C 3.0
btn.Click += (object sender, EventArgs e) => lblResult.Text = "Hello!";
btn.Click += (object sender, EventArgs e) => lblResult.Text = "Hello!";

-orbtn.Click += (sender, e) => lblResult.Text = "Hello!";
btn.Click += (sender, e) => lblResult.Text = "Hello!";
21

Lambda Expressions
=> goes into
separates parameters from method body
can drop parentheses when there is only
one parameter

22

LINQ – C#
Equivalent LINQ queries
query syntax
where c.Contains("Marx")
select c;

method (lambda expression) syntax
var results = Comedians.Where(c => c.Contains("Marx"));

23

LINQ – VB
Equivalent LINQ queries
query syntax
Dim results = From c In Comedians _
Where (c.Contains("Marx")) _
Select c

method (lambda expression) syntax
Dim results = Comedians.Where(Function(c) c.Contains("Marx"))

24

LINQ – Hybrid Syntax
You can also use a hybrid of query and
method syntax
often this is necessary because using query
syntax alone is not expressive enough,
especially when using C#
var results = (from c in Comedians
select c).Count();

25

LINQ to Objects
If an object supports either IEnumerable
or IEnumerable<T> interface, LINQ to
Objects provider enables you to query it
Array, ArrayList, collections, generic
collections, …
System.Linq namespace
All examples shown so far have used
LINQ to Objects
26

LINQ to SQL
System.Data.Linq namespace
Works with SQL Server 2000/2005
Requires entity classes which you can
build using the Object Relational Designer
(ORD)
Entity Framework will let you use LINQ
with other databases using E-R data
models
27

Using ORD (1 of 3)
Add to your App_Code folder

28

Using ORD (3 of 3)
Generated designer.cs file

30

Binding to a LINQ Query
Once the ORD created, you can
reference its DataContext
NorthwindDataContext db = new
NorthwindDataContext();
var results = from cust in db.Customers
where cust.Country == "USA"
orderby cust.CompanyName
select cust;
gvCustomers.DataSource = results;
gvCustomers.DataBind();

Example: CustomersGrid1.aspx

31

Alternately…
You can use LINQ data source

Example: CustomersGrid2.aspx
32

LINQ Tools
LINQPad
free tool for testing LINQ queries
from Joseph Albahari
http://www.linqpad.net/

LINQ Debug Visualizer
free download from Microsoft
http://www.scottgu.com/blogposts/linqquery/
sqlserverqueryvisualizer.zip
33

Selecting Fields
All fields (CustomersGrid1.aspx)
select cust;
Subset of fields –notice use of "new"
to create anonymous type (CustomersGrid3.aspx)
select new
{
cust.CompanyName,
cust.ContactName,
cust.City
};
34

Filtering Data
where (cust.Country == "USA" &&
(cust.CompanyName.ToLower().StartsWith("t") ||
cust.CustomerID.ToLower().StartsWith("t")))
orderby cust.CompanyName
select cust;

Filter1.aspx

35

Using ORD Associations
ORD automatically adds associations for
database relationships
var results = from c in db.Customers
where c.Country == "USA"
select new
{
c.CompanyName,
c.City,
TotalOrders = c.Orders.Count,
LastOrder = c.Orders.Max(o => o.OrderDate)
};

Association1.aspx
36

Associations
You can always get to 1st order
associations
Getting to 2nd and 3rd order associations
requires you to compose your query so
that you traverse 1—m relationships from
the many side to the one side
Contrast
Association1.aspx, and
Association2.aspx
37

Ordering Data
// ascending is default order
orderby cust.Country,
cust.Orders.Count descending
select new
{
cust.Country,
cust.City,
cust.CompanyName,
Orders = cust.Orders.Count
};

Order1.aspx
38

Joining Tables
var results = from order in db.Orders
join detail in db.Order_Details
on order.OrderID equals detail.OrderID
join product in db.Products
on detail.ProductID equals product.ProductID
join customer in db.Customers
on order.CustomerID equals customer.CustomerID
select new
{
customer.CompanyName,
order.OrderDate,
product.ProductName,
detail.UnitPrice,
Cost = detail.UnitPrice * detail.Quantity
};

Join1.aspx

39

Grouping Data
from d in db.Order_Details
from d in db.Order_Details
group new
group new
{
{
order = d.Order,
order = d.Order,
detail = d,
detail = d,
customer = d.Order.Customer
customer = d.Order.Customer
} by d.Order.Customer.CompanyName into grpQuery
} by d.Order.Customer.CompanyName into grpQuery
select new
select new
{
{
Company = grpQuery.Key,
Company = grpQuery.Key,
Purchases = grpQuery.Count(),
Purchases = grpQuery.Count(),
FirstOrder = grpQuery.Min(g => g.order.OrderDate),
FirstOrder = grpQuery.Min(g => g.order.OrderDate),
LastOrder = grpQuery.Max(g => g.order.OrderDate),
LastOrder = grpQuery.Max(g => g.order.OrderDate),
TotalCost = grpQuery.Sum(g => g.detail.Quantity * g.detail.UnitPrice)
TotalCost = grpQuery.Sum(g => g.detail.Quantity * g.detail.UnitPrice)
};
};

Group1.aspx
40

Calling Stored Procedure
Drag sproc from Server Explorer to data
model
Call sproc as method of data context
Example: CustomersFromSproc.aspx
var customersByCountry =
db.procCustomerSelectByCountry(ddlCountry.SelectedValue);
gv.DataSource = customersByCountry;
gv.DataBind();

41

Updating Data
Can update, of course, using sprocs
You can also use LinqDataSource control
Example: UpdateCategories1.aspx

You can also use an ObjectDataSource
control against a Data Access Layer (DAL)
Example: UpdateCategories2.aspx
see excerpt in later slide

This example also illustrates use of LINQ for
SQL Server data paging
42

Using LinqDataSource Control

43

Updating Data Example
public void Update(CategoryDAL cat2Update)
{
var cat = (from c in db.Categories
where (c.CategoryID == cat2Update.CategoryId)
select c).Single();
cat.CategoryName = cat2Update.CategoryName;
cat.Description = cat2Update.Description;
db.SubmitChanges();
}

44

SQL Server Data Paging
public List<CategoryDAL> Select(int startRowIndex, int maximumRows)
public List<CategoryDAL> Select(int startRowIndex, int maximumRows)
{
{
var cat = (from category in db.Categories
var cat = (from category in db.Categories
orderby category.CategoryID
orderby category.CategoryID
select new
select new
{
{
category.CategoryID,
category.CategoryID,
category.CategoryName,
category.CategoryName,
category.Description
category.Description
}).Skip(startRowIndex).Take(maximumRows);
}).Skip(startRowIndex).Take(maximumRows);
List<CategoryDAL> catList = new List<CategoryDAL>();
List<CategoryDAL> catList = new List<CategoryDAL>();
foreach (var c in cat)
foreach (var c in cat)
{
{
CategoryDAL cd = new CategoryDAL();
CategoryDAL cd = new CategoryDAL();
cd.CategoryId = c.CategoryID;
cd.CategoryId = c.CategoryID;
cd.CategoryName = c.CategoryName;
cd.CategoryName = c.CategoryName;
cd.Description = c.Description;
cd.Description = c.Description;
catList.Add(cd);
catList.Add(cd);
}
}
return catList;
return catList;
}
}

45

Other LINQ Providers
LINQ to XML
LINQ to DataSets (aka LINQ to ADO.NET)
LINQ to Entities

46

LINQ to DataSets (aka LINQ to ADO.NET)
Grab data from ADO.NET and put it into a
DataSet, DataTable
Use LINQ to shape the data

47

LINQ to DataSet Example
Example: LINQ2Dataset.aspx
cnx = new SqlConnection(strCnx);
cnx = new SqlConnection(strCnx);
sda = new SqlDataAdapter("procCustomersSelect", cnx);
sda = new SqlDataAdapter("procCustomersSelect", cnx);
sda.SelectCommand.CommandType = CommandType.StoredProcedure;
sda.SelectCommand.CommandType = CommandType.StoredProcedure;
dt = new DataTable();
dt = new DataTable();
sda.Fill(dt);
sda.Fill(dt);
var cust = from c in dt.AsEnumerable()
var cust = from c in dt.AsEnumerable()
orderby c.Field<string>("ContactName")
orderby c.Field<string>("ContactName")
select new
select new
{
{
Contact = c.Field<string>("ContactName"),
Contact = c.Field<string>("ContactName"),
Company = c.Field<string>("CompanyName"),
Company = c.Field<string>("CompanyName"),
Location = c.Field<string>("City") + ", " +
Location = c.Field<string>("City") + ", " +
c.Field<string>("Country")
c.Field<string>("Country")
};
};
48

Other LINQ Providers
LINQ to Entities
Takes O/RM much further than LINQ to SQL
Part of Visual Studio SP 1

49

Discussion Points
When are LINQ's strengths?
What are its weaknesses?
Is LINQ the future of data access in .NET?
Or is the more "classic" N-tier, ADO.NET,
stored procedures approach make more
sense in many scenarios?

50

LINQ Resources
LINQPad
http://www.linqpad.net/

LINQ Debug Visualizer
http://www.scottgu.com/blogposts/linqquery/
sqlserverqueryvisualizer.zip

Scott Guthrie's Blog
http://weblogs.asp.net/scottgu/

51

Thank You!
Slides and samples can be downloaded
from
www.deeptraining.com/litwin

52

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