ActiveX Data Object

ISYS 562

ADO

• An ActiveX controlActiveX is build upon COM, a contract that defines a standard interface by which objects communicate.

• ADO works with several different DBMSs.– Can use ODBC DSN.

A Client/Server Access Application

Access Application Database ServerRequest

Response

Using ODBC

• Windows 2000/2003: • Control Panel /Administrative

Tools/DataSource(ODBC)

• Three types of data source names– System DSN

Using ADO

• Must reference ADO objects. In VBE:– Tools/Reference/

• click Microsoft ActiveX Data Object library 2.7

ADO Object Model

• There are three main objects on which the ADO object models is built:– Connection object: make connection to the

database.– Command object: run SQL against the

database.– Recordset object: holds some or all of the

records in database.

ADO Programming Object Model

Connection

Errors

Command

RecordSet

Error

Parameters Parameter

Fields Field

Connection with a Connection Object

• A connection object represents a unique session with a data source.

• Connection string: database, OLE DB provider, password, if any, security, etc.

• Use the Open method to open a connection.• Use the Execute method to execute SQL.• Manage transaction: BeginTrans,

CommitTrans, rollBackTrans.

Providers

• MSDASQL – Microsoft OLE DB Provider for ODBC

• Microsoft.Jet.OLEDB.4.0

• MSDAORA – For Oracle

• SQLOLEDB – Microsoft SQL Server

Connecting String

• Containing information about database, OLE DB provider, password, if any, security, etc.

• For Jet database:– Dim cn As ADODB.Connection

– Set cn = New ADODB.Connection

– cn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.mdb;")

ODBC DSN Connection

• When using the ODBC provider, the connection string can be a DSN. For example:– Dim Cn as ADODB.Connection

– Set Cn = New ADODB.Connection

– cn.Open ("provider=msdasql;dsn=mySalesDB")

Connection Object Methods• OPEN

cn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.mdb;")

Close• Execute:

– Return a recordset after executing a SQL Select statement.

– Usually is used to execute SQL Insert and Delete that don’t return set of records.

• Demo

Command Objects Properties & Methods

• Command object properties:– ActiveConnection: Current connection – CommandType: adCmdText, adCmdTable,

adCmdStoredProc, etc.– CommandText: Table name if command type is

adCmdTable, SQL statement if command type is adCmdText.

• Command object methods:– Execute

Creating ADO Recordset Objects

• Connection object’s Execute method

• Command object’s Execute method

• Recordset’s Open method

Types of Recordset

Creating Recordset Using ConnectionForwardOnly

Option Explicit

Dim cn As ADODB.Connection

Dim rs As ADODB.Recordset

Private Sub Form_Load()

Set cn = New ADODB.Connection

cn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.mdb;")

Set rs = cn.Execute("select * from customer", adCmdText)

Creating Recordset Using Command ForwardOnly

Option Explicit

Dim cn As ADODB.Connection

Dim rs As ADODB.Recordset

Dim cm As ADODB.Command

Private Sub Form_Load()

Set cn = New ADODB.Connection

cn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.MDB;")

Set cm = New ADODB.Command

cm.CommandType = adCmdText

cm.CommandText = "select * from customer“

Set cm.ActiveConnection = cn

Set rs = cm.Execute

Text1 = rs.Fields(0)

Text2 = rs.Fields(1)

End Sub

Creating Recordset Using Recordset’s Open Method

(Can open any type of recordset)

Dim cn As ADODB.ConnectionSet cn = New ADODB.Connectioncn.Open ("provider=msdasql;dsn=mySalesDB")Dim rs As ADODB.RecordsetSet rs = New ADODB.Recordsetrs.Open "customer", cn, adOpenKeyset ‘Table or SQLDim rc As IntegerDo While Not rs.EOFrc = rc + 1rs.MoveNextLoopMsgBox (rc)

Recordset Properties

• BOF, EOF• BookMark• CursorLocation• CursorType• LockType• MarshalOption• MaxRecords• RecordCount• Sort

Recordset Methods• AddNew, Update, Delete

• Find: Search a recordset.

• MoveFirst, MoveLast, MoveNext, MovePrevious

• Requery: Re-Execute the query.

• GetRows: Fetch records to an array.

Recordset Events

• FetchProgress, FetchComplete• WillChangeField, FieldChangeComplete• WillMove, MoveComplete• WillChangeRecord,

RecordChangeComplete• WillChangeRecordset,

RecordsetChangeComplete• EndOfRecordSet

Using SQL with ADO• SQL Select commands:

– Connection object’s Execute method

– Command object’s Execute method

– RecordSet object’s Open

• SQL Update commands: Insert, Delete, Update– Connection object’s Execute method

• Cn.Execute “Update EmpFile Set Salary = Salary*1.05”

– Command object’s Execute methodsqlSTr = " Update EmpFile Set Salary = Salary*1.05”cm.CommandType = adCmdTextcm.CommandText = sqlSTrcm.ActiveConnection = cncm.Execute

Private Sub Form_Load()Dim cn As ADODB.ConnectionSet cn = New ADODB.Connectioncn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.mdb;")'cn.Open ("provider=msdasql;dsn=mySalesDB")Dim rs As ADODB.RecordsetSet rs = New ADODB.Recordsetrs.Open "select cid from customer", cn, adOpenKeysetDo While Not rs.EOFList0.AddItem (rs.Fields("cid"))rs.MoveNextLoopEnd Sub

Private Sub List0_Click()Dim cn As ADODB.ConnectionSet cn = New ADODB.Connectioncn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.mdb;")'cn.Open ("provider=msdasql;dsn=mySalesDB")Dim rs As ADODB.RecordsetSet rs = New ADODB.Recordsetrs.Open "select cname from customer where cid = '" & List0 & "'", cn, adOpenKeysetMsgBox (rs.Fields(0))End Sub

• Dim rating As String• If Frame13 = 1 Then• rating = "A"• ElseIf Frame13 = 2 Then• rating = "B"• Else• rating = "C"• End If• db.Execute ("update customer set rating='" & rating & "'

where cid='" & List0 & "'")• Text9 = rating

Recordset’s AddNew

– A form with unbound textboxes is initialized for input.

– After entering data, a Save/Add button is clicked and the event handler uses a pair of AddNew and Update methods to insert record.

• Note: We can also use SQL Insert

Unbound Control Input ExamplePrivate Sub Command8_Click()Dim cn As ADODB.ConnectionSet cn = New ADODB.Connectioncn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.mdb;")'cn.Open ("provider=msdasql;dsn=mySalesDB")Dim rs As ADODB.RecordsetSet rs = New ADODB.Recordsetrs.Open "customer", cn, adOpenDynamic, adLockOptimisticWith rs .AddNew .Fields("cid") = Text0 .Fields("cname") = Text2 .Fields("city") = Text4 .Fields("rating") = Text6 .UpdateEnd WithEnd Sub

Find Method

• Syntax: adoRecordsetName.Find criteria• Only accept simple comparison criteria.• Example:

– recordset.Find “CID = ‘” & txtCID & “’”

• Finding employees hired between 2/15/2000 and 5/15/2000:– Adodc1.recordset.Find “Hdate > #2/15/2000#”Then use IF statement in program to filter out those hired after 5/15/2000

Note: Search starts from the current position. To search from the beginning, must do: MoveFirst

If no match is found, the EOF of the recordset will be set to True.

Note: The search starts from the current position of the recordset. To start from the beginning, use the MoveFirst method.

Find Code Example

Dim searchID As StringsearchID = InputBox("enter searchID:")rs.MoveFirstrs.Find "cid='" & searchID & "'"If Not rs.EOF Then Text0 = rs.Fields("cid") Text2 = rs.Fields(1)Else MsgBox ("not found")End If

Demo

Using the BookMark

• Bookmark is a variant type property that keeps the current recordset’s position. This position can be saved in a variant variable and later go to that position.

BookMark Example

To save bookmark:

Dim BkMark As VariantPrivate Sub Command5_Click()

BkMark = rs.BookmarkEnd Sub

To go to the saved bookmark location:

Private Sub Command6_Click()rs.Bookmark = BkMarkText0 = rs.Fields("cid")Text2 = rs.Fields("cname")

End Sub