Vb .Net Dataaccesss Vii

8/10/2019 Vb .Net Dataaccesss Vii

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VB .NET Database Access


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Microsoft Universal Data Access

ODBC: Open Database Connectivity

A driver manager

Used for relational databases

OLE DB: The OLE database protocol

Allows a program to access information in many typesof data source.

Data provider: databases, spreadsheets, etc.

ADO.NET: ActiveX Data Objects

An Interface for OLE DB.

Allow programmers to use a standard set of objects torefer to any OLE DB data source.


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.Net Applications

OLE DB

Provider

OLE DBData Source

OLE DB

Provider

ODBC

ODBC

Data Source

SQL Server

Data Source

SQL Server

.Net Data Provider

OLE DB

.Net Data Provider

ADO.Net


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Using ODBC

Windows 2000/2003: Control Panel /Administrative Tools/DataSource(ODBC)

Three types of data source names User DSN: usable only by you and only on the machine

currently using.

System DSN: Any one using the machine can use.

File DSN: Can be copied and used by other computerswith the same driver installed.


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VB.NET Database Tools

Database connection: Tool/Connect to database

Provider:MS Jet 4.0 OLE DB Provider

Connection

Server Explorer Data connections:

Right click and Add Connection

Tables, Views

Toolbox:Data tab

Data Form Wizard


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Steps to Retrieve Data

Establishes a connection to the database.

Executes commands against the database.

Store data results.


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ADO.NET Objects

Data Set

.NET Applications

Data Reader

Command Object

Connection Object

Database

Adapter


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ADO.NET Objects

Connection Object: Represent a connection to thedatabase.

Command Object: The command object allows usto execute a SQL statement or a stored procedure.

DataReader: It is a read-only and forward-onlypointer into a table to retrieve records.

DataSet Object: A DataSet object can hold several

tables and relationships between tables. DataAdapter: This the object used to pass data

between the database and the dataset.


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How to create an ADO.Net object?

Using Wizard

Data Form Wizard

Data Adapter Wizard

Using code:

Example:

dim strConn as string ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source =c:\sales2k.mdb"

dim objConn as new OledbConnection(strConn)

objConn.open()


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Data Form Wizard

Creating a form with ADO.Net objects and data-

bound controls to display and update information

in a dataset. Demo: Using Data Form Wizard to create a

navigational form.

Project/Add Windows Form/Data Form Wizard

Set connection

Choose tables

Display records in grid or in text boxes.


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Adapter & Dataset Context Menu

Adapter:

Properties:

Command objectsConfigure Adapter

Generate dataset

Preview data

Dataset:

View Schema: Dataset/XML


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Other Data Form Demos

Display records in text boxes.

Add /Modify/Delete records.

Hierarchical forms:

Parent/Child relationship


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Creating A Database Application

Without Programming Creating a database application to display

information and update database.

A main form with buttons to open dataforms:

DisplayInfo

Enter New

Modify

Exit


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Data Binding

Connect a control or property to one or more data

elements.

Simple binding: Use simple binding to display afield value in controls that show Data Bindings in

the property window, such as text box or label.

Complex binding: Use complex binding to bind

more than one field to controls such as DataGrid

and list box. Use the controls Data Source and

Data Member to bind the data.


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Creating Bound Controls

DataGrid control:

Data Source property

Data Member property

In the Form Load event, use Adapters Fill

method to load the dataset:

OleDbDataAdapter1.Fill(DataSet11)


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Binding Text Box

Data Bindings property:

Text: choose field

Add navigation buttons:

The current record position within the dataset is

stored in a forms BindingContexts Position

property. This position is zero based. Add onemove to the next record, minus one move to the

previous record.


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MoveNext and MoveLast Example

MoveNext:

Me.BindingContext(DataSet21, "customer").Position += 1

MoveLast:

Me.BindingContext(DataSet21, "customer").Position =Me.BindingContext(DataSet21, "customer").Count -1

How to MovePrevious and MoveFirst? Note: The Position property takes care of the end of file

automatically.


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CurrencyManager

Dim custCurrMgr As CurrencyManager

Dim ordCurrMgr As CurrencyManager

In a procedure: ordCurrMgr = Me.BindingContext(Ds31, "orders")

custCurrMgr = Me.BindingContext(Ds31, customer")

custCurrMgr.Position += 1 ordCurrMgr.Position += 1


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Binding DataGrid

From Server Explorer, drag the table from adatabase connection (or from Data tab, drag

a oleDbAdapter) onto the form. Create dataset.

Drag DataGrid and set the DataSource andData Member property.

Use adapters Fill method to load thedataset.


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Displaying Many Tables with

One DataGrid Define one Adapter for each table.

Create the dataset with multiple tables.

Add a DataGrid control and set the

DataSource proeprty to the dataset name

and leave the DataMember property blank.


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Creating Hierarchical Data Grid

Define two Adapters, one for the parent table andone for the child table.

Create the dataset.

Right-click the dataset to View Schema

Right-click the parent table and choose Add/NewRelation

Add a DataGrid control and set the DataSource

proeprty to the dataset.parentTable and leave theDataMember property blank.

Note: DO File/SaveAll after creating the relation.


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Binding ListBox

Example: Bind Customer Tables CID field to alistbox.

Create a Adapter to retrieve CID (and Cname) fields ,and generate the dataset.

Add ListBox and set binding properties: Data Source

Display Member

Value Member: the actual values for items in the list box. Todisplay the selected items value in a text box, do:

Textbox1.text = ListBox1.SelectedValue

Can we use TextBox1.text=ListBox1.SelectedItem?

No!


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Display Selected Record

Bound textbox:

Me.BindingContext(DataSet11,

"customer").Position = ListBox1.SelectedIndex

Unbound textbox


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ListBox SelectedItem Property

How to display the selected record in unboundtextbox?

After binding to a data source, this property return aDataRowView object.

What is DataRowView? Object Browser:

System.Data System.Data

DataRowView: Item property

To retrieve a column from a DataRowView object(use 0-based index to identity a column):

ListBox1.SelectedItem.Item(1)

Or: ListBox1.SelectedItem(1)

Or: ListBox1.SelectedItem(Cname)


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Using Object Browser

View/Object Browser

DataSet object model:

System.Data DataSet

Relations

Tables

Rows

Columns

Use Object Browser to study objects properties,methods.


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Collection Structure

Properties:

Count

Item(index), 0-based index

Methods:

Clear, Add, Insert, Remove, etc.


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Navigate and Display Records in

Unbound Text Boxes Use code to assign field value to the text

boxs text property.

Example: Dim drFound As DataRow

drFound = DataSet11.CUSTOMER.Rows(0)

Or DataSet11.Tables(CUSTOMER).Rows(0)

TextBox4.Text = drFound.Item("cname") Or drFound.Item(1)

Or: TextBox4.Text =DataSet11.CUSTOMER.Rows(0).Item(1)

Or: DataSet21.Tables.Item("customer").Rows.Item(0).Item(1)


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Implement MoveNext Button

with Unbound ControlIf rowIndex < DataSet11.CUSTOMER.Rows.Count-1 Then

rowIndex += 1

TextBox1.Text = DataSet11.Tables("customer").Rows(rowIndex).Item(0)

TextBox2.Text = DataSet11.CUSTOMER.Rows(rowIndex).Item(1)

Else

MsgBox("out of bound")

End If

Note: MovePrevious, MoveLast, MoveFirst?


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Using Object Browser to Study OleDB

Object System.Data

System.Data.OleDB

OleDBConnection

Methods: New(), New(ConnectionString), Open(), Close()

Properties: ConnectionString, DataBase, Provider, TimeOut

OleDBCommannd

Methods: ExecuteReader, ExecuteNonQuery

Properties: Connection, CommandType, CommandText,

Parameters OleDBDataAdapter

Methods: Fill

Properties: SelectCommand, InsertCommand, DeleteCommand,UpdateCommand.


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Searching with the Find MethodAnother Way to Bind Listbox and Display

Selected Record

Create an adapter to retrieve Customer

records and create a dataset.

Bind the CID field to the listbox.

Use the Find method of Tables Rows

collection to find the record.

Display the found record in unbound text

boxes.


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Code Example

Private Sub ListBox1_SelectedIndexChanged(ByVal sender AsSystem.Object, ByVal e As System.EventArgs) HandlesListBox1.SelectedIndexChanged

Dim drFound As DataRow

drFound = DataSet41.CUSTOMER.Rows.Find(ListBox1.SelectedValue)

Assume SelectedValue is CID

TextBox1.Text = drFound.Item("cname")TextBox2.Text = drFound.Item("rating")

End Sub

Note: We can get the search value from other controls such as InputBoxand Textbox.


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How to Determine If Record Exists

or NotDim foundRow As DataRow

Dim SearchValue as String

SearchValue=InputBox(Enter CID)

foundRow = DataSet41.CUSTOMER.Rows.Find(SearchValue)

If Not (foundRow Is Nothing) Then

TextBox1.Text = drFound.Item("cname")

TextBox2.Text = drFound.Item("rating")

ElseMessagerbox.show(Record not exist)

End If


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Creating Parameter Query with Adapter

Configuration Wizard Parameter query: Selection criteria is entered at

run time.

Command objects Parameters property.

Example: Orders table: OID, CID, Odate,SalesPerson

To create a parameter for the CID field: In the Query Design windows criteria column of the CID field, add

criteria: =?

To assign the parameter value: OleDbDataAdapter2.SelectCommand.Parameters("cid").Value =

Demo: Get CID from a InputBox and display orders.


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Parameter Query Example:

Select CID from a listBox and displayorders of the selected CID in a DataGrid Create and bind the listbox (specify the valueMember).

Create a second adapter and define a parameter query.

In the Query Design windows criteria column, add criteria: =?

Generate a 2nd dataset (DataSet21 in this example) with theparameter.

Create and bind the DataGrid to the dataset.

In the listboxs SelectedIndexChanged event, assign the selectedvalue to the parameter and fill the dataset:

DataSet21.Clear() OleDbDataAdapter2.SelectCommand.Parameters("cid").Value =ListBox1.SelectedValue



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Display Selected Record in Text Boxes

with Parameter Query Create and bind the listbox.

Create a second adapter and define a parameter query. In the Query Design windows criteria column, add criteria: =?

Generate the dataset with the parameter. Create and bind textboxes to the dataset.

In the listboxs click event, assign the selected value to theparameter and fill the dataset: DataSet11.Clear()

OleDbDataAdapter2.SelectCommand.Parameters("cid").Value =ListBox1.SelectedValue



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Send Changes in a Bound DataGrid

Back to the Database Updating records in DataGrid:

New records are added at the end of the grid.

To delete a record, click the leftmost column to selectthe record, then press the delete key.

Modify record

Add an Update button that use adapters update

method to send changes back to the data source: OledbDataAdapter1.Update(Dataset11)


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Creating Parent/Child Form with

Binding Dataset contains Customer and Orders with

relation CustomerOrders.

Bind the textboxes to Customer table.

Bind the datagrid to the relation:

DataSource: Dataset

DataMember: Customer/CustomerOrders

Note: Study the form created by the Data FormWizard.

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Vb .Net Dataaccesss Vii