Net Framework 3 5

 

Net Framework 3 5

 

 

 

This course includes

? LINQ Overview

? Access array? Access set? Query projection

? Use a Lambda expression? Query operator

 

 

Agenda

? LINQ overview? Access array? Access set? Query projection

? Use a Lambda expression? Query operator

 

 

Data access problems

Data! = Object

 

 

Data access status

Sqlconnection c = new sqlconnection (...);

Queries in quotes

C. Open ();

Sqlcommand cmd = new sqlcommand (

@ "Selectc. Name, C. Phone

Arguments

From MERs C

Loosely bound

Where c City = @ P0"

);

Cmd. Parameters. addwithvalue ("@ po", "London"); datareader DR = C. Execute (CMD );

Results loosely

While (dr. Read ()){

Typed

String name = dr. getstring (0); string phone = dr. getstring (1)

Datetimedate = dr. getdatetime (2)} Dr. Close ();

Compilercannot help

Catch mistakes

 

 

Data Access Method

Classes describe

Public Class Customer

Data

{

Public int customerid;

Encapsulated

Public string name;

Business

Public String city;

Validation

Public void validate (){

Query is natural

// Todo: add business Validation

Part of

}

Language

}

Gridview1.datasource = from customer in db. MERs

Wherecustomer. City = "London"

Select customer;

The Compiler

Provides

Gridview1 databind ();

Intelliisense and

Type-checking

 

 

LINQ Project

C #

VB

Others...

. Net Language Integrated Query (LINQ)

LINQ enabled data sources

LINQ enabled ADO. net

LINQ

LINQ

LINQ

LINQ

LINQ

To objects

To Datasets

To SQL

To entities

To XML

<Book>

<Title/>

<Author/> <price/>

</Book>

Objects

Relational

XML

 

 

Agenda

? LINQ Overview

? Access Array

? Access set? Query projection

? Use a Lambda expression? Query operator

 

 

Query Arrays

Array implements

Ienumerable <t>

String [] cities = {"Auckland", "Oslo", "sysydney ",

"Seattle", "Paris", "Los Angeles "};

Ienumerable <string> places = from city in cities

Wherecity. length> 5

Orderby city descending select city;

Gridview1.datasource = places; gridview1.databind ();

LINQ Query

Expression Using

Query Operators

Ienumerable <string>

Sequence result can be

Used w/databinding

 

 

Bind to page

 

 

Agenda

? LINQ overview? Access Array

? Access set

? Query projection

? Use a Lambda expression? Query operator

 

 

Custom City class

Public class city {

Public string name;

Public String country;

Public int distancefromseattle;

}

List <city> locations = getlocations ();

 

 

Query the city collection

Collection implements

Ienumerable <t>

List <city> locations = getlocations ();

Ienumerable <city> places = from city in locations

Wherecity. distancefromseattle> 1000 orderby city. country, city. Name selectcity;

Gridview1.datasource = places; gridview1.databind ();

Ienumerable <city> return sequencedetermined by select statement

 

 

Bind to page

<Asp: gridview id = "gridview1" autogeneratecolumns = "false" runat = "server">

<Columns>

<Asp: boundfieldheadertext = "country" datafield = "country"/> <asp: boundfieldheadertext = "city" datafield = "name"/> <asp: boundfield headertext = "Dist" datafield = "distancefromseattle"/>

</Columns>

</ASP: gridview>

 

 

Page binding result

 

 

Agenda

? LINQ overview? Access array? Access set

? Query projection

? Use a Lambda expression? Query operator

 

 

Query projection (select)

? Do not return all data columns/attributes? Modify or convert the returned data

? Number of queries supported by the compiler for "anonymous type"

Data column/attribute

? Generate anonymous type ('a)

 

 

Use anonymous type

List <city> cities = cityutilityhelper. getcities ();

VaR places = from city in cities

Where city. distancefromseattle> 1000 select new {

City = city. Name,

Country = city. Country,

Distanceinkm = city. distancefromseattle * 1.61

};

Gridview1.datasource = places; gridview1.databind ();

Anonymous type used to custom shape dataresults and apply miles-> kilometer Conversion

 

 

Anonymous Type Binding

<Asp: gridview id = "gridview1" autogeneratecolumns = "false" runat = "server">

<Columns>

<Asp: boundfieldheadertext = "country" datafield = "country"/> <asp: boundfieldheadertext = "city" datafield = "city"/> <asp: boundfieldheadertext = "dist (km) "datafield =" distanceinkm "/>

</Columns>

</ASP: gridview>

 

 

Anonymous binding result

 

 

Agenda

? LINQ overview? Access array? Access set? Query projection

? Use a Lambda expression? Query operator

 

 

Use a Lambda expression

? The query syntax is a convenient abbreviation of declarative code.

You can write it manually:

? Ienumerable expr = names

. Where (S => S. Length = 5)

. Orderby (S => S)

. Select (S => S. toupper ());

 

 

Delegate declaration of lambda expressions

? The Lambda expression is the natural evolutionary result of the C #2.0 anonymous method.

Func filter = delegate (string s ){

Return S. Length = 5;

};

Func extract = delegate (string s ){

Returns;

};

Func project = delegate (string s ){

Returns. toupper ();

};

Ienumerable expr = names. Where (filter)

. Orderby (extract)

. Select (project );

 

 

Expression Tree

? The expression tree is the data representation in the effective memory of the lambda expression.

It makes the structure of the expression transparent and explicit. ? Assign a Lambda expression to a variable of expression type

, Field or parameter, the compiler will issue the Expression Tree.

Binaryexpression body = (binaryexpression) filter. Body; parameterexpression left = (parameterexpression) body. Left; constantexpression right = (constantexpression) body. Right;

Console. writeline ("{0} {1} {2}", left. Name, body. nodetype, right. value );

 

 

Definition of the query operator where

? Public static class SEQUENCE {

Publicstatic ienumerable where (this ienumerable source, func predicate ){

Foreach (T item in source)

If (predicate (item ))

Yield return item;

}

}

 

 

Call

? To call the extension method in a common way:

? Ienumerable <string> query =

Enumerable. Where (names, S => S. length <6 );

? C # language allows us to use the following method to call extensions

Method:

? Ienumerable <string> query = names. Where (S =>

S. length <6 );

 

 

Agenda

? LINQ overview? Access array? Access set? Query projection

? Use a Lambda expression

? Query operator

 

 

Standard query operator

? Sorting and grouping

-Orderby & groupby

? Aggregation

-Count-sum

-Average-max

-Min

? Projection

Select & selectworkflow

 

 

Query syntax

? The existing foreach Statement of C # uses the. NET Framework

The ienumerable/ienumerator method provides declarative syntax for iteration. The foreach statement is completely optional, but it has been proved to be a very convenient and commonly used language mechanism.

? The query syntax uses declarative syntax for the following most common query operations:

It simplifies the query expression: Where, select, selectmany, groupby, orderby, thenby, orderbydescending, and thenbydescending.