Chapter 6 Working with Data in a Connected Environment

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VB.Net 2005 - Chapter 6 1
Chapter 6
Working with Data in a
Connected Environment
VB.Net 2005 - Chapter 6
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Chapter 6

Lesson 0: Connected & Disconnectd Environment
in ADO.NET

Lesson 1: Creating and Executing Command
Objects

Lesson 2: Working with Parameters in SQL
Commands
Note: Lesson 3: BLOBs and Lesson 4: Bulk Copy: For reading at
home
Lesson 5: Performing Transactions by Using the Transaction Object
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Lesson 0: Connected & Disconnectd
Environment in ADO.NET

2 ways using with ADO.NET
Connection Data Adapter
Data
Source
DataSet

Web
Form
Windows
Form
Connection Command
Data
Source
DataReader
Web
Form
Windows
Form
Disconnectd
Connected
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Disconnected Data Access
 Single database server
can support many users

reduced server's
resources
 Data using more flexible
 Data not 'tied' to a
connection

easy to pass
between tiers or
persist to file
 Highly suited to Web and

n-tier Apps

Expensive when
open, close
connections

Retrieving large
result sets can be
very slow

Places demand on
client memory and
CPU
Advantages
Disadvantages
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System.Data Architecture
DataReader
Database
Program
DataProvider
DataSet
DataAdapter
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Details:
System.Data Architecture
Command Object

Connection Object
Program
Provider
DataSet
DataReader
DataAdapter
Database
Action SQL
Maintain
data
Maintain
data
Get data
Get data
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Main Difference:DataSet-DataReader
DataSet

Data structure to store schema and data in a disconnected
fashion

Useful for editing data offline and later update to data
source

DataReader

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
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Differences DataSet and DataReader
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Lesson 1: Creating and Executing
Command Objects

1.What Are Command Objects?

2.Creating and Configuring Command
Objects

3.Creating SQL Commands (SQL
Statements) with the Query Designer
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Lesson 1: Creating and Executing
Command Objects

1.What Are Command Objects?
6

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Lesson 1: Creating and Executing
Command Objects

1.What Are Command Objects?

To execute SQL statements,stored procedures

Contain the necessary information to execute
SQL statements
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Lesson 1: Creating and Executing
Command Objects

1.What Are Command Objects?

Depend on Data Providers
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Lesson 1: Creating and Executing
Command Objects

1.What Are Command Objects?

Common properties (p.254)

CommandText


SQL string, table name, proc name

CommandType

Text

Proc

Table

Connection

Parameters
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Lesson 1: Creating and Executing
Command Objects

1.What Are Command Objects?

Common Command Object Methods (p.255)

ExecuteNonQuery

ExecuteReader

ExecuteScalar
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Lesson 1: Creating and Executing
Command Objects

2.Creating and Configuring Command
Objects

Creating a Command Object That Executes a
SQL Statement

Creating a Command Object That Executes a
Stored Procedure

Creating a Command Object That Performs
Catalog Operations

Creating a Command Object That Returns a
Single Value
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Lesson 1: Creating and Executing
Command Objects

2.Creating and Configuring Command
Objects

Creating a Command Object That Executes a
SQL Statement (p.256)
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Lesson 1: Creating and Executing
Command Objects

2.Creating and Configuring Command
Objects

Creating a Command Object That Executes a
Stored Procedure (p.257)
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Lesson 1: Creating and Executing
Command Objects

2.Creating and Configuring Command
Objects

Creating a Command Object That Performs
Catalog Operations (p.257)
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Lesson 1: Creating and Executing
Command Objects

2.Creating and Configuring Command
Objects

Creating a Command Object That Returns a
Single Value (p.258)

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Lesson 1: Creating and Executing
Command Objects

3.Creating SQL Commands (SQL
Statements) with the Query Designer

Creating SQL Commands (SQL Statements)
with the Query Designer

Performing Database Operations Using
Command Objects
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Lesson 1: Creating and Executing
Command Objects

3.Creating SQL Commands (SQL
Statements) with the Query Designer

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.

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Lesson 1: Creating and Executing
Command Objects

3.Creating SQL Commands (SQL
Statements) with the Query Designer

Performing Database Operations Using
Command Objects (p 260)
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How to receive DataReader
Connection
ConnectionConnection
Connectionn
nn
n
Command
CommandCommand
Commandn
nn
n
DataReader
DataReaderDataReader
DataReadern
nn
n
Open

Which data?
Result
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DataReader Class

Store the information obtained by the command

In stateless stream type object

Very efficient

Forward-only cursor

Read-only cursor
Dim dr as OLEDBDataReader = cmd.ExecuteReader
Do while dr.Read()
msgbox dr("City").toString
Loop
dr.Close
Datareader and MS Access
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DataReaders

You can’t access anything until you call
Read()the first time
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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

GetString(i) :
returns the value of the i
th
column as the
specified type
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DataReader method/property
conSinhVien.Open()
cmdSinhVien = New OleDbCommand("Select ", conSinhVien)
drSinhVien = cmdSinhVien.ExecuteReader
Do While drSinhVien.Read
MessageBox.Show(drSinhVien.GetString(0))
Loop

drSinhVien.Close()
conSinhVien.Close()
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Note: DataReader

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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Note about DataReader


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
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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.

While sdr.Read
strProductName = sdr.GetString(0)

sb.Append(strProductName)
sb.Append(sdr.GetDecimal(1).ToString())
sb.Append(vbTab)
sb.Append(sdr.GetInt16(2).ToString())
End While
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Lesson 1: Creating and Executing
Command Objects

3.Creating SQL Commands (SQL
Statements) with the Query Designer

Lab: P265
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Lesson 2: Working with Parameters in
SQL Commands

1.What Is a Parameter and Why Should I
Use Them?

2.Types of Parameters

3.Creating Parameters

4.Adding Parameters to Command
Objects
17

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Lesson 2: Working with Parameters in
SQL Commands

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.
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Lesson 2: Working with Parameters in
SQL Commands

2.Types of Parameters (p 274)

Input parameter. (default)

Output parameter.

InputOutput parameter.


InputOutput parameters are used to both send and
receive data when executing a command.

The type of parameter is designated in the
Direction property of the parameter

With a parameter, we ou can set its Direction
property to Input, Output, InputOutput, or
ReturnValue.
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Lesson 2: Working with Parameters in
SQL Commands

3.Creating Parameters (p 274)

Create parameters:instance of the Parameter
class

setting its name and data type

Choose ParameterDirection
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Lesson 2: Working with Parameters in
SQL Commands

4.Adding Parameters to Command

Objects

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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Lesson 2: Working with Parameters in
SQL Commands

Lab: Lab: Working with Parameters page
275
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Lesson 2: Summary

Update Database with connect mode

Client

Type 1: Using client dynamic Sql

Type 2: Using client SQL with parameters

Server


Using server Query Parameters

Using server Stored Procedured

Example: find student
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Your Questions?
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
cmd.CommandText = "select *
from sinhvien where ten like
‘%tuan%' "

cmd.CommandText = "select *
from sinhvien where ten like ‘%” &
txt.text & “%' "
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
cmd.CommandText = "select *
from sinhvien where ten like
‘%tuan%'"

cmd.CommandText = "select *

from sinhvien where ten like ‘ %
tuan %' "
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Notes

Datareader: New?????

Open Connection before ExecuteReader

Execute only one for one command
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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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Ex. Insert new record
Exit

Save
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Access

Insert into sv(ma,lname,fname,phone) Values
(?,?,?,?)

Cmd.parameters.add(p1)

Cmd.parameters.add(p2)

Cmd.parameters.add(p3)

Cmd.parameters.add(p4)

Insert into sv(ma,lname,fname,phone) Values
(@ma,@lname,@fname,@phone)

insert into sv(ma,[last name],[first
name],phone) values (?,?,?,?)
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Exer 2

Copy Exer 1 to new folder

Change the way to get data


Client Dynamic SQL -> Client Parameters SQL
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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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Exer 4

Using Student data file

Display in treeview

Display detail
0904981234
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BT1

LOP(MaLop,TenLop)

SINHVIEN(MaSV,Ten,DiaChi,SDT,Lop)