Chapter 6 Working with Data in a Connected Environment

VB.Net 2005 - Chapter 6 3 2 ways using with ADO.NET Connection Data Adapter Data Web Form Windows Form Connection Command Data Web Form Windows Form Disconnectd Connected VB.Net 2005 -

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VB.Net 2005 - Chapter 6 3

2 ways using with ADO.NET

Connection Data Adapter

Data

Web Form

Windows Form

Connection Command Data

Web Form

Windows Form

Disconnectd

Connected

Disconnected Data Access

Single database server

can support many users

reduced server's

resources

Data using more flexible

Data not 'tied' to a

Retrieving large result sets can be very slow

Places demand on client memory and CPU

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Like Phone connection.

Doesn’t need to store data in memory

Object to access data in a connected, forward-only,

read-only fashion

When performance is your chief concern, especially with

large amounts of data, use a DataReader class

Differences DataSet and DataReader

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1.What Are Command Objects?

2.Creating and Configuring Command

Objects

3.Creating SQL Commands (SQL

Statements) with the Query Designer

Lesson 1: Creating and Executing

Command Objects

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To execute SQL statements,stored procedures

Contain the necessary information to execute

SQL statements

Command Objects

Depend on Data Providers

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Common Command Object Methods (p.255)

ExecuteNonQuery

ExecuteReader

ExecuteScalar

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Creating SQL Commands (SQL Statements)

with the Query Designer

Performing Database Operations Using

Command Objects

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Creating SQL Commands (SQL Statements)

with the Query Designer

We can use the Query Designer to assist in creating

SQL for Command objects

Select database in Server Explorer-> select New

Query from the Data menu

Command Objects

Performing Database Operations Using

Command Objects (p 260)

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Store the information obtained by the command

In stateless stream type object

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You can’t access anything until you call

Read()the first time

Core DataReader method/property

Read: Reads, and set pointer to the next record.

Close

IsClosed

HasRows: Returns true if DataReader contains rows

FiledCount: Number of columns

GetName(i): returns the label of the ith column in the

current row

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ADO.NET does not provide all the server-side cursor

Don’t keep DataReaders open longer than necessary

For flexible updates & client-side manipulation…

Use DataSets and DataAdapters

Only one DataReader use at a time

Tie to Connection=> cannot used other DataReader

To reuse connection=>call DataReader.Close

Don’t depend on the garbage collector-> explicitly

close.

Tie the connection ‘ life to DataReader

CommandBehavior.CloseConnection in ExecuteReader

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The first row of data is not available until you

call the Read method

Using with stored procedure uses a return or

output parameter, must close DataReader

before get parameter

DataReader cannot be used for data binding

System.DBNull.value

Note about DataReader

Use Item collection, to get values:

Using index instead of by key (column name).

Using native type instead of using the Item collection followed by

an explicit cast

sdr.GetDecimal(1) instead of CDbl(sdr.Item("UnitPrice")).

Concat field’ values: A large of operation

Using StringBuilder instead string concatenation.

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1.What Is a Parameter and Why Should I Use

Them?

parameter can be thought of as a type of variable

use to pass and return values between your

application and a database

Parameter data types are assigned using the types

defined in the System.Data.SqlDbType enumeration

pass parameter values to SQL statements when we

want to change the criteria of your queries quickly

Lesson 2: Working with Parameters in

InputOutput parameters are used to both send and

receive data when executing a command

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Command objects have a Parameters property

that represents a collection of parameters

After you create a parameter, you must add it

to the Parameters collection of the Command

object

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Type 1: Using client dynamic Sql

Type 2: Using client SQL with parameters

Server

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Datareader: New?????

Open Connection before ExecuteReader

Execute only one for one command

Exer 1

1 Create MA access database

Table Student(ID,FirstName,Lastname,Phone)

Using Client dynamic SQL to put data in Listview

Using Client dynamic SQL to detail data to

Textboxes

Exit

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Exit Save

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Copy Exer 1 to new folder

Change the way to get data

Client Dynamic SQL -> Client Parameters SQL

Exer 3

Copy Exer 2 to new folder

Change the way to get data

Client Parameters SQL ->server Parameters SQL

in querry

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