ActiveX Data Object ISYS 562

ADO An ActiveX control ActiveX 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 ApplicationDatabase Server Request 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 Connection ForwardOnly 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.Connection Set cn = New ADODB.Connection cn.Open ("provider=msdasql;dsn=mySalesDB") Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset rs.Open "customer", cn, adOpenKeyset ‘Table or SQL Dim rc As Integer Do While Not rs.EOF rc = rc + 1 rs.MoveNext Loop MsgBox (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 method sqlSTr = " Update EmpFile Set Salary = Salary*1.05” cm.CommandType = adCmdText cm.CommandText = sqlSTr cm.ActiveConnection = cn cm.Execute

Private Sub Form_Load() Dim cn As ADODB.Connection Set cn = New ADODB.Connection cn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.mdb;") 'cn.Open ("provider=msdasql;dsn=mySalesDB") Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset rs.Open "select cid from customer", cn, adOpenKeyset Do While Not rs.EOF List0.AddItem (rs.Fields("cid")) rs.MoveNext Loop End Sub Private Sub List0_Click() Dim cn As ADODB.Connection Set cn = New ADODB.Connection cn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.mdb;") 'cn.Open ("provider=msdasql;dsn=mySalesDB") Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset rs.Open "select cname from customer where cid = '" & List0 & "'", cn, adOpenKeyset MsgBox (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 Example Private Sub Command8_Click() Dim cn As ADODB.Connection Set cn = New ADODB.Connection cn.Open ("provider=microsoft.jet.oledb.4.0;data source=c:\salesDB.mdb;") 'cn.Open ("provider=msdasql;dsn=mySalesDB") Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset rs.Open "customer", cn, adOpenDynamic, adLockOptimistic With rs.AddNew.Fields("cid") = Text0.Fields("cname") = Text2.Fields("city") = Text4.Fields("rating") = Text6.Update End With End 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 String searchID = InputBox("enter searchID:") rs.MoveFirst rs.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 Variant Private Sub Command5_Click() BkMark = rs.Bookmark End Sub To go to the saved bookmark location: Private Sub Command6_Click() rs.Bookmark = BkMark Text0 = rs.Fields("cid") Text2 = rs.Fields("cname") End Sub