2.  2 Data Object Library approaches ◦ DAO (Data Access Objects)  Original access strategy (up to VB6)  Closely linked to MS Access ◦ ADO (ActiveX Data Objects)  Newer approach  More generic  Same approach for ASP (VB Script active server pages)

3.  Jet Database Engine: VB’s database engine for MS Access & ISAM (Indexed Sequential Access Method) DBMSs  ODBC (Open Database Connectivity): Interface for SQL relational databases  RDO (Remote Data Objects): Original component to access databases across a network  OLE DB (Object Linking & Embedding Databases): newer generic interface accessing SQL & nonSQL databases

4. VISUAL BASIC 6.0 APPLICATION ADO OLE DB ODBC SQL DATA NON SQL DATA OTHER e.g. MS Access (JET) Text Files, Excel LEGACY SQL Server, ORACLE etc SYSTEMS

5.  Data Control based ◦ non-programming ◦ associated with form based controls (DataGrid, DataList etc) ◦ Limited control over data  Programming based ◦ uses Connection object (ADO) ◦ allows closer data control

6.  Under Project|References ◦ Microsoft ActiveX Data Objects 2.5 Library  Under Project|Components (added to Toolbox) ◦ Microsoft ADO Data Control 6.0 (OLEDB) ◦ Microsoft Data Grid Control 6.0 (OLEDB) ◦ Microsoft Data List Controls 6.0 (OLEDB)  DataList  DataCombo

10.  Data Control Object (Adodc1) ◦ Connection String - Click expansion button & build connection ◦ Record Source - SQL query (SELECT * FROM emp;)or table (emp) ◦ Command Type - 1-adCmdText for SQL query 2-adCmdTable for table  Textbox (Text1) ◦ Data Source - Adodc1 ◦ Data Field - ename

11.  Requires ADO object library setup (Project|References)  Requires creation, setup & opening of variables for ◦ Connection object (using Connection String) ◦ Recordset object (Using SQL Query/Table)  Recordset Processing  Close Recordset & Connection

12. Dim adoconn As ADODB.Connection Dim recset As ADODB.Recordset Set adoconn As New ADODB.Connection Set recset As New ADODB.Recordset adoconn.Open “Provider=Microsoft.Jet.OLEDB.4.0; _ Data Source=C:\projemp.mdb; User ID=Admin;Password=” recset.Open “emp”, adoconn, adOpenDynamic Do Until recset.EOF List1.AddItem recset!ename recset.MoveNext Loop recset.Close adoconn.Close

13.  Connection Object  Recordset Object  Field Object  Command Object  Parameter Object  Error Object

14.  Connection String ◦ Provider (e.g. Provider = Microsoft.Jet.OLEDB.4.0;) ◦ Data Source (e.g. Data Source = C:\db\projemp.mdb;) ◦ Username & Password (e.g. User ID = Admin; Password = ;)  Dim As ADODB.Connection  Set = New ADODB.Connection .Open ConnectionString  Other Connection Methods ◦ Close, Cancel ◦ Execute (CommandText, RecordsAffected, Options)  CommandText can be SQL query ◦ BeginTrans, CommitTrans, RollbackTrans  Transaction commands for starting, ending and undoing stored transactions if required

15.  Two dimensional array holding a table/result of SQL  ADO allows four different cursor types (ways of using recordsets) ◦ Dynamic Cursor (CursorType = adOpenDynamic)  moves freely through recordset (forwards, backwards, BOF, EOF)  all appends, updates, deletes made by other users seen by recordset and can be changed by recordset (slow) ◦ Keyset Cursor (CursorType = adOpenKeyset)  Similar to dynamic - allows viewing of records changed by other users but disallows changes on those records (slow) ◦ Static Cursor (CursorType = adOpenStatic)  cannot see other users’ changes (hence works faster) ◦ Forward Only Cursor (CursorType = adOpenForwardOnly)  like static cursor but no backwards recordset movement (fastest)

16.  Dim rst As ADODB.Recordset  Set rst = New ADODB.Recordset  Recordset Methods ◦ AddNew, Delete, Update ◦ Open, Close, Cancel  rst.Open,,  e.g. Rst.Open “emp”, adoconn, ◦ Move, MoveFirst, MoveNext, MovePrevious, MoveLast ◦ Seek - searches the index and moves to the row with required value ◦ Find - searches for row with required value (seek is faster but requires index) ◦ Requery - runs query recordset is based on again

17. Dim fld As Field rst.Open “emp” ‘table emp from projemp database put into recordset rst Set fld = rst.Fields(1) ‘assign 2nd recordset field(ename) to fld Debug.Print fld.Name ‘prints the field name in Immediate window Debug.Print rst.Fields(2) ‘prints current record value for 3rd field (salary) Debug.Print rst.Fields.(“ename”) ‘prints current record value for ename Debug.Print rst.Fields.Count ‘prints number of fields in tecordset rst

18. Assuming Connection (conn) to projemp.mdb & recordset (rst) rst.Open “SELECT * FROM emp;”, conn Print “eno”, “ename”, “salary”, “dno” Do Until rst.EOF Print rst(0), rst(1), rst(2), rst(4) rst.MoveNext Loop rst.Close conn.Close

19. Assuming Connection (conn) to projemp.mdb & recordset (rst) rst.Open “SELECT * FROM emp;”, conn rst.Find = “ename = ‘smith’ ” Print rst.Fields(0), rst.Fields(1) ‘ prints 1st &2nd fields (eno&ename) for ‘ record found

20.  Queries the data source and returns a recordset ◦ Dim com As ADODB.Command Set com = New ADODB.Command com.ActiveConnection "Provider=Microsoft.Jet.OLEDB.4.0;_ Data Source=D:\projemp.mdb;User ID=Admin;Password=” com.CommandText = “SELECT * FROM workscom.CommandType = adCmdType Set rst = com.Execute ◦ Alternatively can use a stored procedure (query created in data source)comCommandText = “Query1” ‘query defined in projemp.mdbcomCommandType = adCmdStoredProc  Performs SQL INSERTs, UPDATEs etc to alter data source