Language Integrated Query potx

HO CHI MINH UNIVERSITY OF INDUSTRYprivate void btnNoi_Click object sender, EventArgs e... HO CHI MINH UNIVERSITY OF INDUSTRY public static int SumFrom1toN this int n {… } public static

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HO CHI MINH UNIVERSITY OF INDUSTRY

LINQ

Language Integrated

Query

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2 New features in language:

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2.1 Implicitly Typed Variables

– Declare variables without specifying their type

– Strongly type, not variant, not object

– Visual Studio will determine type

• Predict what the compiler will choose

• Intelligence support

– Type inference -> most general

• “3/10/2010” -> string, not date

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{ var x = 113;

var y = "1/1/2012" ;

var z = 1.7;

var k = new DateTime (2012, 1, 1);

string msg = "x type=" +x.GetType() + "\n" +

"y type = " +y.GetType() + "\n" +

"z type =" +z.GetType() + "\n" +

"k type = " + k.GetType();

MessageBox Show(msg);

}

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– Always declare the type if we know

– Implicitly Typed Variables are suited for LINQ and anonymous type

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2.2 Object Initializers

 Constructor

 Allow to assign values to object properties (fields) when create object

 We do not have to explicitly invoke a constructor

 Useful in any context

– Especially useful in LINQ expressions

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public int a2 { set ; get ;}

public int b2 { get ; set ; }

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2.3 Anonymous Types

– Set property values to object without writing class definition

– The resulting class has no usable name

– Class name is generated by compiler, inherits from Object

– The result: an anonymous type that is not available at source code level

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– Need a temporary object to hold related data

– Don’t need method

– If we need a different set of properties for each declaration

– If we need to change the order of properties for each declaration

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– Need to define methods

– Need to define another variable

– Need to shared data across methods

private void btn4_Click( object sender, EventArgs e)

{

var teo = new { ID=1234,Name= "Tèo Hả Tèo" };

MessageBox Show(teo.ID + "-" +teo.Name);

}

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2.4 Extension Methods

 Special kind of Static method

 Allow the addition of methods to an existing class

– Without creating a new derived type

– Without re-compiling or modifying the original type

 Called The Same way regular methods are called

 Define in static class

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MessageBox Show(n.SumFrom1toN()+ "" );

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namespace StudyLinQ

{

public static class MyExtensionMethod

{

public static int SumFrom1toN( this int n){…}

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private void btnNoi_Click

( object sender, EventArgs e)

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public static int SumFrom1toN( this int n) {… }

public static string NoiChuoi( this string s1, string s2){…}

public static void ChangeColorToRed( this Button btn)

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btnColor.ChangeColorToRed();

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public delegate int ChangeInt ( int x);

public int Tang2( int x){ return x + 2;}

public int Giam2( int x) { return x - 2;}

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2.4.a Delegate

private void btndlg_Click

( object sender, EventArgs e)

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2.4.a delegate: why?

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private void btnEven_Click( object sender, EventArgs e)

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private bool isPrime( int x)

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public static class MyExtensionMethod

{

public delegate bool HandleFunction ( int x);

public static void SelectItemInListBox(this ListBox lst,

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private bool isEven( int x)

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private void btnEven_Click( object sender, EventArgs e)

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2.4.a delegate: with anonymous

private void button7_Click

( object sender, EventArgs e)

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2.4.a delegate: with anonymous

Exercise:

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2.5 Lambda Expressions

– A function without a name

– Perform action , return a single value

– Can be used wherever a delegate type is valid

– Allow a function’s caller to define the action

– Not just pass parameters

– Lambda expressions provide a clearer syntax for anonymous delegates

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2.5 Lambda Expressions: delegate

 Syntax

– parameters => expression

– a functional superset of anonymous methods

– Lambda expressions can "infer" parameter types, even if you omit them

– Lambda expressions can use both statement blocks and expressions

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2.5 Lambda Expressions in C#

– Read as “goes to”

– x=>x+3 if x=1 then 4 is returned

– x=> x==5: if x=5, True is returned

– (x,y)=> x+y if x=2, y=4 then 6 is returned

– (x,y)=>x==y if x=2, y=4 then False is returned

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2.5.a lambda example

private void button8_Click

( object sender, EventArgs e)

{

ChangeInt d=(( int x)=>x+2); //lambda expression

ChangeInt d1 = (k => k + 2); //lambda expression

ChangeInt d2 = delegate ( int x) //anonymous method

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2.5.b delegate: turn back to example: lambda

private void btnEven_Click( object sender, EventArgs e)

{

listNumber.SelectItemInListBox(x => x % 2 == 0);

}

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3 LINQ

Language Integrated Query

LINQ does create a new way of looking at enumerations of data, and

gives out-of-the-box functionality for them

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3 LINQ example 1

int [] nums = new int [] { 1,1,3,2,5,0,9,8,9};

var result =from n in nums

Output 1 1 3 5 9 9

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3 What is LINQ

 a programming model that introduces queries as a first-class concept

 SQL-like syntax used in LINQ is called a query expression

 provides a set of standard query operators

 common tasks: query, ordered, grouped or aggregated from an existing

in-memory collection, a database, an XML file or many other sources

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3 What is LINQ

- Compiler generates code

• More detail: later

string [] list = new string [] { "teo" , "ty" , "bin" , "bo" };

var ret1 = from c in list

where c.StartsWith( "t" )

select c;

IEnumerable < string > ret2 = list.Where(c=>c.StartsWith( "t" ));

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3 What is LINQ: Language Integration

var ret1 = from c in list

where c.EndsWith( "o" )

orderby c

select new {Id=c.ElementAt(0),Name=c };

var ret2 = list

Where(c => c.EndsWith( "o" ))

OrderBy(c => c)

Select(c=> new { Id=c.ElementAt(0),Name=c});

string [] list = new string [] { "teo" , "ty" , "bin" , "bo" };

foreach ( var c in ret1){

Console WriteLine(c.Id + " - " +c.Name);

}

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3 What is LINQ: LINQ Flavors

Covers many data domains

These implementations is defined through a set of extension methods

The access to these features is controlled by the imported namespaces

Can be extended to support other data domains

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3 What is LINQ: Everywhere

 LINQ to Objects, LINQ to SQL, and LINQ to XML

 LINQ is an extendable technology

– open-source product: LINQ Extender

• build your own LINQ extensions

 Other providers

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3 What is LINQ: Everywhere

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3 LINQ:

New features of.NET framework support for LINQ:

– Extension methods, lambda expressions

• are used extensively to build queries

– Anonymous types : to allow data to be returned from a query without the need

to first define a class or structure,

– Generics : creation of various types of collection

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3 LINQ syntax example

?????

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3 LINQ basic: Query syntax vs

Method syntax

Performance???

Query syntax => Method syntax

Have to "redeclare" person each time in the lambda expressions query syntax is a lot more readable than method syntax

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3 LINQ basic: Query syntax vs

Method syntax

• Use the Query Expression syntax wherever possible, its easier to read;

• If you need to mix the Extension Methods with Query Expressions, put them

at the end;

• Keep each part of the Query Expression on separate lines

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4 LINQ: Exercise

Convert CSV (comma separated values )

string to int array

– S =“20;10;2;0;1;0”

– => array of int {20,10,2,0,1,0}

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5 LINQ Execution

– Queries that return a single value or object do execute immediately

However, those that return a list of items are usually not executed until the first time that the results are used

Lazy means "don't do the work until you absolutely have to."

Deferred means "don't compute the result until the caller actually uses it."

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5 LINQ Execution

If you want a query to

be realized immediately, Call ToList, ToArray or any of the other operators that need to enumerate the entire sequence to return a result.

var source = new List < string > { "A" , "B" , "C" };

var values = from c in source

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6 LINQ to Object

Foreach

Performs the specified action on each element of the specified array or list (It

doesn’t actually use the System.Predicate delegate Instead, it uses the similar System.Action delegate

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Exists

Determines whether the specified array or list contains any elements that

match the conditions defined by the specified predicate

Find

Searches for an element that matches the conditions defined by the specified predicate and returns the first occurrence within the entire Array or List

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Searches for an element that matches the conditions defined by the specified

predicate and returns the zero-based index of the first occurrence within the

array

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FindLast

Searches for an element that matches the conditions defined by the specified

predicate and returns the last occurrence within the entire array or list

FindLastIndex

Searches for an element that matches the conditions defined by the specified predicate and returns the zero-based index of the last occurrence within the array

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Determines whether every element in the array or list matches the conditions

defined by the specified predicate

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• Returns elements from a sequence as long as a specified condition is true

The element's index is used in the logic of the predicate function

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PetshopDataContext db = new PetshopDataContext ();

var query = ( from p in db.Products

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//loop through all of the controls

foreach ( Control c in this Controls)

{

//make sure the control is Textbox

if (c is TextBox )

{

//cast that "control" object to the TextBox and disable

}

var textBoxes = this Controls.OfType<TextBox>();

this Controls.OfType< TextBox >().ToList().

ForEach(c=>c.Enabled= true );

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7 LINQ to SQL: Concepts

 Created to bridge the differences between relational data and CLR object

 Mapping Classes to Tables

– Using code or Graphical Designer for Mapping

– Creating Entity Classes

Tableclass, Rowobject

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Using the Graphical Designer for Mapping

– Server connection

– Adding a designer file (dbml): LINQ to SQL Classes

– Drag drop from Server Explorer design surface

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Right click on project/ add new item / LINQ to SQL classes to create .dbml

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7 LINQ to SQL: Actions

var cateQuery = from cate in db.Categories

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Table < Category >cates=db.GetTable< Category >();

var query = from c in cates

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var query = db.Categories

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7 LINQ to SQL: Actions Insert

//create new cate 1 and 2 product

Category cat1 = new Category ();

pro2.Name = "Remote XYZ" ;

cat1.Products.Add(pro1); //add product to cat

cat1.Products.Add(pro2);

db.Categories.InsertOnSubmit(cat1); //add cat

db.SubmitChanges(); //Save database change

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cat.Name = "New Byard";//Change name

//Ask the DataContext to save all the changes

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var products = db.Products.Where

(p => p.ProductId.Contains( "pro" ));

db.Products.DeleteAllOnSubmit(products);

db.SubmitChanges();

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var query = from pro in db.Products

join cat in db.Categories

on pro.CategoryId equals cat.CategoryId

select new

{

Id=pro.ProductId, Name=pro.Name };

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var products = db.GetListProductByCatalog( "birds" );

foreach ( var pro in products)

{

Console WriteLine(pro.Name);

}

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PetshopDataContext db = new PetshopDataContext ();

var query = from p in db.Products

Console WriteLine(c.Pro Name);

foreach ( var l in c.List)

Tiêu đề	Language Integrated Query Potx
Trường học	Ho Chi Minh University of Industry
Chuyên ngành	Computer Science
Thể loại	Lecture Notes
Thành phố	Ho Chi Minh City

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