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WORKING WITH DATABASES II

Using SQL Server DBs + Visual Basic

Objectives

To discuss:

Data-Related Objects including

SqlConnection

DataSetDataTables

DataAdapterDataReader

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Objectives

Howto

connect to a database,

create and populate a DataTable,and

navigate therecordsin theDataTable.

Manipulatedata

edit records

add records

delete records

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The DataGridViewControl

A convenient tool for displaying the contents ofdatabase tablesin rowsand columns.

Data bindingis used tolink database tables tocontrolsona programsforms.

Special objects called components provide thelinkingmechanism.

When you link a control to a database, a wizard

guidesyou throughtheprocess.We will use several data-related objects

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Data Objects5

Data-Related Objects

Datasource

Usually a database but can also be a textfile, Excel spreadsheet, XML file, or Webservice

Keeps track of the database name, location,username, password, and other connectioninformation.

Our data sources will be MSSQL Serverdatabase files

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TableAdapter

Pulls data from one or more database tables andcopiesit into a DataSet

Can

selectsome or all table rows,

add/ insert new rows,

deleterows, and

modify existing rows.UsesSQLqueries to retrieve and update database

tables.

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DataSet

In-memorycopyofdatapulled fromdatabase tables.Virtual container for your tables

Anapplicationcanmodify rowsin the DataSet,

add new rowsto the DataSet, and

delete rowsfromthe DataSet.

Changes to DataSets become permanent when anapplication uses a TableAdapter to write the

changesfromthe DataSet back to the database.DataSets can get data from more than

one datasourceand from more thanone TableAdapter.

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DataTable

Table inside a DataSet

Holdsdata generated by a TableAdaptersSELECTquery.

Has a Rows collection that corresponds todatabase table rows.

You can loop through the Rows collection andinspect or modify individual column values withineachrow.E.g. loop through the rowsand add up a Totalscolumn.

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BindingSource

Optional.

Provides a link between a DataSetand oneor more controlsona form.

These controls are called data-boundcontrols.

If the user modifies the data in a control, theBindingSource can copy the changes to the

DataSet.

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Conceptual View11

2-way Data Flow Between a Data Source and an Application Working with a Database12

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ADO.NET

ADO.NET (Active Data Objects)is the database technology forMicrosofts.NETplatform.

ADO.NETObjects:

Together, the following objectsretrieve data froma database:

ADO.NetsObjects

DataSet

DataTable

DataReader

ThetraditionalADOobjects

connection

command

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ADO.NET Objects

ADO.NETObjects

DataSetand

DataTablethese are also optimised for moving disconnected setsof data across

the Internet and intranets, including throughfi rewalls:

a DataReaderresembles a forward-only, read-only RecordSet, found in the older

ADO

In ADO.NET, aDataReader is a broad category ofobjects used tosequentially read data from a data source.

Providesan eff icient way to access data.

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ADO.NET Objects

Thetraditional ADO objects

connectionand

command

E.g.

myReader = myCommand.ExecuteReader();calls the ExecuteReadermethod on an instance of theCommand

object called myCommand in order to create a DataReadercalledmyReader.

The DataReaderretrievesdata (rowsf roma data source)

You use theReadmethod of theDataReaderobject to obtain arowfrom theresultsof the query

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The ADO.Net Object Model16

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Some Data Objects & Their Purpose

SqlConnection

used to establish a connection to an SQL Server datasource.

DataSet

a memory-resident representationof data

There are many ways of working with a DataSet, suchasthroughDataTables.

DataTable holdsa result set of data for manipulation and navigation.

DataAdapter

isused to populatea DataReader.

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MyVBDB18

MyVbDb

Create a newWindowsApplication named MyVbDb.

Right-click Form1.vb in the Solution Explorer window,choose Rename, and then change the name of thedefault formtoMainForm.vb.

Next, set the forms Text property to My DatabaseExample.

All the ADO.NET objects, except the DataTable, arepart of the System.Data namespace.

The DataTable is part ofSystem.Xml.

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Remember this?Namespaces The Microsoft .NET Framework contains a largelibrary of classesthat

make it possible to write applications for desktop computing, mobileapplications, and the Web.

The classesare grouped by similarity into namespacesto make it easier tofind them.

A namespaceisa logical container that holdsclassesof similar types.

For example,

theSystem.Collections namespacecontains classes related to buildingcollections(arrays, l ists, dictionaries,sets).

The System.Windows.Forms namespace contains classes related tobuilding desktop applicationsfor Windows.

All the ADO.NET objects, except the DataTable, are part of theSystem.Datanamespace.

The DataTableispart ofSystem.Xml.OOP

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MyVbDb

All the ADO.NET objects, except the DataTable, are

part of theSystem.Datanamespace.

The DataTable is part of System.Xml.

We add referencesto bothnamespacesso that youcan use thenamespaceswithouthavingtotypethefullnamespacequalifier.

1. From the Menu bar, choose Project, MyVbDbPropertiesto display the Project Properties.

2. Click theReferences tab to display the activereferences for the project, as shown in the figure in

thenext slide.

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MyVbDb22

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MyVbDb

3. Inthe lower part of thispage isa checkbox list of imported namespaces.

Use the scrollbar f or this list box (not the main scrollbar for the page) tolocate and check

System.Data,

System.Data.SqlClient, and

System.Xml.

System.Data isprobably already checked and will appear toward thetop ofthelist.

If not, locateit and check it.

System.Data.SqlClient and System.Xml will most l ikely not be checked, andwillbe toward thebottomof the list.

4. Click SaveAll onthe toolbar.

5. Click theMainForm.vb [Design]tab to returnto the FormDesigner.

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MyVbDbConnecting to a Database

To access the data in a database, you must firstestablishaconnection.

using anADO.NETconnectionobject.

Multiple connection objects are included in the .NETFramework, including:

TheOleDbConnection object(for working with OLE DBdata providers)

Object Linking and Embeddingis a proprietary technology developedby Microsoft that allows embedding and linking to documents andother objects

theSqlConnectionobject (for optimised access to MicrosoftSQLServer).

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As we will connect to a Microsoft SQLDatabase, youll be using the SqlConnectionobject.

Example:

A statement suchas:

DimcnADONetConnectionAsNew SQLConnection()

Creates an object variable of type SqlConnectionand

Initialisesthe variable to a new connection.

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For MyVbDb you will create a module-levelvariableto hold the connection.

Double-click the form now to access its events, andplace the cursor below the class definitionstatementat the top of themodule.

Enter the following statement:

Private myCn As New

SQLConnection()

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Before using thisconnection, you must specify the datasourceto whichyouwant to connect.

This isdone through theConnectionStringpropertyofthe ADO.NETconnection object.

The ConnectionString contains connectioninformationsuchas

the name of the provider,

username,and

password.

The ConnectionString might contain manyconnectionparameters

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MyVbDbSome Parameters for the SQL ConnectionString

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the set of parameters availab le varies, depending on the source of data to whichyoureconnecting.

If youspecify multipleparameters,separate themwitha semicolon.

In our case, Microsoft SQL.

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TheProvider= parameter is one of the mostimportant at this point; it depends on the typeof database youre accessing.

In our example, you access a Microsoft SQLdatabase, so you use the provider information forMicrosoft SQL

In addition to specifying the provider, you alsoneed to specify the database.

We will use the Test.mdfdatabase.

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Specify the ConnectionString property of yourADO.NET connection by placing the following statementin your formsLoad event:

myCn.ConnectionString = "Data

Source=.\SQLEXPRESS; AttachDbFilename = " & _

"D:\Test.mdf;Integrated Security=True;

Connect Timeout=30;" & _

"User Instance=True "

The code assumes that youve placed the database in

the D: drive. Change it to suit your ownpath.

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After the connection string is defined, you establisha connection to a data source by using the Open()methodof theconnectionobject.

Add the following statement to theLoad event, rightafter the statement that sets the connectionstring:

myCn.Open()Different types of data sources and different versions of different data sources have diff erent

connection information. The best way t o determine the connection string is to consult the online

documentation for the data source to which you want to attach i.e. if you are not using M icrosoft SQL

Server databasescheck onlinef or information on connectionstrings for other data providers.

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MyVbDbClosing a Connection to a Data Source

Do not rely on a variable going out of scope to close aconnection to a data source.

Instead, youshould forcean explicit disconnectvia code.

write code to explicitly close theconnectionwhenthe formis closed

Call the Close()method of the connectionobject.

1. Open the object drop-downlist in the code window and selectMainFormEventsif it isnt already selected.

2. ChooseFormClosed from the event dropdown list to createan event handler for the FormClosedevent.

3. Enter thefollowing statementsin theFormClosed event:

myCn.Close()

myCn.Dispose()

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The DataTableObject

Manipulating Data33

DataTableObjects

A DataTable object containsthe result set of a table,query,or stored procedure.

The easiest way to manipulate data/ records whenusing ADO.NET.

Use a DataTable object to manipulate records:

add,

edit,

delete,

find

navigate

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DataTables

DataTablescontain a snapshot of the data in thedata source.

To populate a DataTable, you must create anSqlDataAdapter.

We usually

first populate a DataTable, using theDataAdapterobjectsFill() methodthen

manipulate its results, and

f inally send the changesback to the data source (the db inthiscase) using the SqlDataAdaptersUpdate() method.

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DataTables

Any changes made to the DataTableappear only in the local copy of the datauntil youcall the Update method.

Q:Whyhavealocalcopyof thedata?

Reduces contention by preventing users fromblocking otherswho want to read the data in

thedata source.

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DataAdapters

To populate a DataTable, you must createan SqlDataAdapter.

The DataAdapter

uses the connection youve already definedto connect to the data sourceand then

executesa query youprovide.

The results of that query are pushed intoa DataTable.

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DataAdapters

The .NET Framework has many connection

objects including: the Ol eDbConnection object

and the SqlConnection object.

It has multiple ADO.NET DataAdapter objectsaswell.

Youll use the SqlDataAdapterbecause youwillbe connecting to Microsoft SQLServer.

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Creating DataAdapters

The constructor for an SqlDataAdapter has thefollowingsyntax:

Dim daSqlDataAdapter As NewSqlDataAdapter([CommandText],[Connection])

The constructor hasoptional parametres

the command to executewhen filling a DataTableorDataSet

a connectionspecifying thedata source

youcould have multiple connectionsopen in a single project

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Creating a DataAdapter

To add an SqlDataAdapter to your MyVbDbproject:

Private myDA As SqlDataAdapter

Create it as a module-level variable:

i.e.intheclassheader

, not in the Load event

Add this statement immediately below thestatement youentered to declare themyCnobject

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Add the following statement at the bottom ofthe forms Load event (immediately followingthestatement that openstheconnection):

myDA = New SqlDataAdapter("Select *

From Contacts", myCn)

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You will use theSqlDataAdapter toupdate theoriginal datasource.

Therefore you must specify the insert,update, anddeletestatements to use to submit changes fromthe DataTable to thedata source.

ADO.NET lets you customise how updates are submitted byenabling you to manually specify these statements asdata base commandsorstored procedures.

Usually (and also for the case of MyVbDb), we let ADO.NETautomatically generate these statements by creating aCommandBuilder object.

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To create the CommandBuilder module level variable, enterthisstatement in theclassheader:

Private myCB As SqlCommandBuilder

Af ter you initialise a CommandBuilder object it handles theupdating,inserting,anddeletingof databehind the scenes.

To make this work, you have to attach the CommandBuilder toanSqlDataAdapter.

passan SqlDataAdapter to the CommandBuilder.

The CommandBuilder then registers forupdateeventson theSqlDataAdapter and provides the insert, update, and deletecommandsasneeded.

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To initialise theCommandBuilderobject add thefollowing statement to the end of the Form_Loadevent

myCB =New SqlCommandBuilder(myDA)

See the next slide for how your code looks like so

far.

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MyVbDb45

Summary of Steps So Far

Since you jump around a lot in this example follow the stepsexactly:

1. Create amodule-levelvariabletoholdtheconnection(i.e.instantiateaconnectionobject)

PrivatemyCnAsNewSQLConnection()

2. Specifythedatasourceyoureconnectingtheobjectto

by specifying theConnectionString propertyof your ADO.NETconnection(give theparametresof theConnectionString property)

Placethefollowing statement in your formsLoadevent:

myCn.ConnectionString="DataSource=.\SQLEXPRESS;AttachDbFilename=" &_

"D:\Test.mdf;IntegratedSecurity=True;ConnectTimeout=30;"&_

"UserInstance=True"

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3. Establish the connection between the connection objectandthedatasourceby adding the following statement to theLoadevent:

myCn.Open()

4. Explicitly disconnect the connection object fromthe datasourceby calling the Close()method of theconnectionobject. Open the object drop-down list in the code window and selectMainForm

Eventsif it isnt already selected.

Choose FormClosed fromthe event dropdown list to create an event handler fortheFormClosedevent.

Enterthe following statementsin theFormClosed event:

myCn.Close()

myCn.Dispose()

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5. Toenableyoutofill yourDataSetand/orupdateyourdatasource, add an SqlDataAdapter to your project.

Create a module-level object variable of typeSqlAdapter

PrivatemyDAAsSqlDataAdapter

6. Initialise the SqlAdapter object variable to a newSqlDataAdapter and pass to its parametres the commandtext and connection.

Add the following statement to the formsLoadevent:

myDA = New SqlDataAdapter("Select * From Contacts",myCn)

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MyVbDb

The codeyouhave writtenso far

accessesa database and

creates a DataTable that can be usedanywhere in the class.

Your class should now look like theone shownin the next slide.

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MyVbDb54

Summary of Steps So Far (cont)

9. Declaring a newmodule-level DataTable objectthat willhold a referenceto data

PrivatemyDataTableAsNewDataTable

10. Use an integer variable to keep track of the users currentposition (row) within theDataTable.

Add the following statement immediately below the statement youjust entered:

PrivatemyRowPositionAsInteger=0

11. To f ill the DataTable with data add the following statement

to the formsLoadevent, after theexisting code:myDA.Fill(myDataTable)

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Referencing Fields in a DataRow56

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Referencing Fields in a DataRow

DataTablescontain a collection ofDataRows.

To access a row within the DataTable, you specify theordinal (index) of that DataRow.

For example, to accessthe first row of your DataTable:

DimmyDataRowAsDataRow=myDataTable.Rows(0)

Data elements in a DataRow are called columns.

For example, the Test.mdf databasesContactstable has 2columns:

ContactName

State

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To reference the value of a column, you can pass thecolumnname to the DataRow like this:

Change the value of the column.

myDataRow(ContactName) =JohnJuma

Or

Get the value of the column.

strContactName=myDataRow (ContactName)

NB: If you misspell a column name, an exception occurs when the statement

executes at runtime;no errors are raised at compile time.

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Create a procedure to display the currentrecordinthedatatable.

1. Position the cursor after the End Substatement of the MainForm_FormClosedevent, and press Enter a few times to createsome blank lines.

2. Enter the procedure onthe next slide:

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Private Sub ShowCurrentRecord()

If myDataTable.Rows.Count = 0 Then

txtContactName.Text = ""

txtState.Text = ""

Exit Sub

End If

txtContactName.Text = _

myDataTable.Rows(myRowPosition)("ContactName").ToString()

txtState.Text = _myDataTable.Rows(myRowPosition)("State").ToString()

End Sub

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3. Ensure that the first record in the DataTable isshownwhenthe formfirst loads

Add this statement to the Form_Load event, after theexistingstatements:

Me.ShowCurrentRecord()

To display the data, you must add a few controls tothe form.

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Referencing Fields in a DataRow62


Press F5 to run the project. The first contact in the Contactstable isdisplayed in the text box:

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Navigating Records

The ADO.NETDataTable object supportsa number ofmethods that canbe used to accessits DataRows.

The simplest of these is the ordinal accessor that youused in your ShowCurrentRecord()method.

theprocedureyoucreatedtodisplaythecurrentrecordinthedatatable.

The DataTable has no dependency on the source ofthe data.

Therefore, this same functionality is availableregardlessof where the data comesfrom.

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Navigating Records65

Navigating Records

3. Double-click the button, and add the following codeto itsClick event:

' Move to the first row and show the data.

myRowPosition = 0


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' If not at the first row, go back one row and show the record.

If myrowPosition > 0 ThenmyRowPosition = myRowPosition - 1


End If

btnMovePrevious


' If not on the last row, advance one row and show the record.

If myRowPosition < (myDataTable.Rows.Count - 1) ThenmyRowPosition = myRowPosition + 1


End If

btnMoveNext

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' If there are any rows in the data table, move to the last

' and show the record.IfmyDataTable.Rows.Count > 0 Then

myRowPosition = myDataTable.Rows.Count - 1

Me.ShowCurrentRecord()End If

Editing Records

To edit records in a DataTable, you change thevalue of a particular column in the desiredDataRow.

Remember

Changes arent made to the original datasource until you call Update() on theSqlDataAdapter, passing in the DataTablecontaining thechanges.

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Editing Records

To add a button that the user can click to updatethecurrent record:

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Editing Records

2. Double-click the Save button, and add thefollowing code to itsClick event:

' If there is existing data, update it.

If myDataTable.Rows.Count 0 Then

myDataTable.Rows(myRowPosition)("ContactName

") = txtContactName.Text

myDataTable.Rows(myRowPosition)("State") =

txtState.Text

myDA.Update(myDataTable)

End If

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Youve updated the DataTable then passed it to the DataAdapters Update Method.

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Creating New Records

Adding records to a DataTable is similar to editingthem.

However, to create a new row in the DataTable, youmust first call the NewRow()method.

After creating the new row, you can set its columnvalues.

The row isnt actually added to theDataTable, however, until you call the Add()methodon the DataTablesRowCollection.

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Modify your interface so that the user can addnewrecords.

Have two textboxesthat will be used for:

the contact name and

thestate.

When the user clicks the button you provide,the valuesin these text boxesare writtento theContactstable asa new record.

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Creating New Records75

Creating New Records76

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5. Double-click the Add button, and add thefollowing code to itsClick event:

Dim drNewRow As DataRow = myDataTable.NewRow()

drNewRow("ContactName") = txtNewContactName.Text

drNewRow("State") = txtNewState.Text

myDataTable.Rows.Add(drNewRow)


myRowPosition = myDataTable.Rows.Count 1


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Notice that after the new record is added, theposition is set to the last row, and theShowCurrentRecord() procedure is called.

This causes the new record to appear in the displaytext boxesyoucreated earlier.

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Deleting Records

To delete a record from a DataTable, you call theDelete()methodonthe DataRowto be deleted.

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Deleting Records

2. Double-click the Delete button, and add thefollowing code to itsClick event:

' If there is data, delete the current row.


myDataTable.Rows(myRowPosition).Delete()


myRowPosition = 0


End If

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MyVbDb81

Your form should now look like this: Running MyVbDb82

Running MyVbDb

PressF5 to runthe project.

If you entered all the code correctly and you placed theContacts database in the D: drive (or modified the path usedin code), the form should be displayed without errors, and thefirst record in the database appears.

Click thenavigationbuttonsto move forward and backward.

Changea contactsinformation; click the Save button

your changesare made to theunderlying database.

Next, enter anewname and state into the New Contact

sectionof the form, and clickAdd. The name is added to the database and displayed in the

appropriate text boxes.

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MyVbDbThe Entire Code

Public ClassMainForm

Private myCnAsNew SqlConnection()

Private myDA AsSqlDataAdapter

Private myCBAsSqlCommandBuilder

Private myDataTable AsNew DataTable

Private myRowPositionAsInteger = 0

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MyVbDbThe Entire CodePrivate Sub MainForm_FormClosed(sender As Object, e As

FormClosedEventArgs) Handles Me.FormClosed

myCn.Close()

myCn.Dispose()

End Sub

Private Sub ShowCurrentRecord()

If myDataTable.Rows.Count = 0 Then

txtContactName.Text = ""

txtState.Text = ""

Exit Sub

End If

txtContactName.Text = _

myDataTable.Rows(myRowPosition)("ContactName").ToString()

txtState.Text = _

myDataTable.Rows(myRowPosition)("State").ToString()

End Sub

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MyVbDbThe Entire CodePrivate Sub MainForm_Load(sender As Object, e As

EventArgs) Handles MyBase.Load

myCn.ConnectionString ="Data Source=.\SQLEXPRESS;

AttachDbFilename = " & _

"D:\Test.mdf;Integrated Security=True; Connect

Timeout=30;" & _

"User Instance=True

myCn.Open()

myDA = New SqlDataAdapter("Select * From

Contacts", myCn)

myCB =New SqlCommandBuilder(myDA)

myDA.Fill(myDataTable)


End Sub

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MyVbDbThe Entire CodePrivate Sub btnMoveFirst_Click(sender As Object, e AsEventArgs) Handles btnMoveFirst.Click

' Move to the first row and show the data.

myRowPosition = 0


End Sub

Private Sub btnMovePrevious_Click(sender As Object, e AsEventArgs) Handles btnMovePrevious.Click

' If not at the first row, go back one row and show therecord.

If myrowPosition > 0 Then

myRowPosition = myRowPosition - 1


End If

End Sub

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MyVbDbThe Entire Code

Private SubbtnMoveNext_Click(sender As Object, e As EventArgs)HandlesbtnMoveNext.Click

' If not on the last row, advance one row and show the record.

If myRowPosition < (myDataTable.Rows.Count - 1) Then

myRowPosition = myRowPosition + 1


End If

End Sub

Private Sub btnMoveLast_Click(sender As Object, e As EventArgs)

Handles btnMoveLast.Click

' If there are any rows in the data table, move to the last and

' show the record.

If myDataTable.Rows.Count > 0 Then

myRowPosition = myDataTable.Rows.Count - 1


End If

End Sub

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MyVbDbThe Entire CodePrivate Sub btnSave_Click(sender As Object, e As

EventArgs) Handles btnSave.Click

' If there is existing data, update it.


myDataTable.Rows(myRowPosition)("ContactName")

= txtContactName.Text

myDataTable.Rows(myRowPosition)("State") =

txtState.Text


End If

End Sub

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MyVbDbThe Entire CodePrivate Sub btnAddNew_Click(sender As Object, e As

EventArgs) Handles btnAddNew.Click

Dim drNewRow As DataRow = myDataTable.NewRow()

drNewRow("ContactName") = txtNewContactName.Text

drNewRow("State") = txtNewState.Text

myDataTable.Rows.Add(drNewRow)


myRowPosition = myDataTable.Rows.Count 1


End Sub

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MyVbDbThe Entire CodePrivate Sub btnDelete_Click(sender As Object, e As

EventArgs) Handles btnDelete.Click

' If there is data, delete the current row.


myDataTable.Rows(myRowPosition).Delete()


myRowPosition = 0


End If

End Sub

End Class

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Key Terms

auto-generated field BindingSource object components compound primary key database databaseschema data binding data-bound control DataGridView control DataSet DataTable data source DataSource property DisplayMember property

foreign key

identity fieldLIKE operatorone-to-many relationship

ORDER BY clauseprimary key

query parameterrelational database modelSELECT statement

Structured Query Language (SQL)TableAdapter

WHERE clausewildcard symbolxcopy deployment

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apii 4b db

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