INT213 Updating the Database

Contents Cursors Locking Updating databases

Cursors So far, we have stepped through a Recordset in the forward direction one record at a time This technique uses the simplest cursor, the forward-Looking-Only cursor A cursor is simply a pointer that indicates your current location in the Recordset

Cursors A cursor points to a specific row BOF A cursor points to a specific row Different types of cursors can Move forward Move backward Move by several rows A cursor cannot Move before the first record (Beginning Of File) Move after the last record (End Of File) Row 1 cursor Row 2 Row n EOF

Cursor Types Cursor Constant Value Description Forward only adOpenForwardOnly Moves forward only, one by one. Fastest performing cursortype, and also the most limited. The forward-only cursor does not support the RecordCount property, and does not support the MovePrevious methods of the recordset object. Static adOpenStatic 3 The result is not updated when changes are made to the database Keyset adOpenKeyset 1 Not applicable to this course Dynamic adOpenDynamic 2 This reevaluates the query each time a new row is requested. Thus, new rows added are detected.

Scrollable Cursors All cursors, except forward-only, are scrollable This means they can move in more than just the forward direction Scrollable cursors support the methods MoveFirst – move to the first record MoveLast – move to the last record MoveNext – move to the next record MovePrevious – move to the previous record Move n – move n records forward or back

Selecting a Cursor RecordSet.Open The cursor is selected via one of the parameters used when opening the RecordSet RecordSet.Open source, (sql statement, stored procedure or table name) connection, (connection string or connection object) cursorType, (How to move through RecordSet) LockType, (Whether to read or write to a table) commandType (describes the source)

Selecting a Cursor To create a static cursor set RS = Server.CreateObject ("ADODB.Recordset") query = "SELECT * FROM Person ORDER BY lastName" RS.Open query, objConn, adOpenStatic To output a RecordSet in reverse rs.MoveLast Do While Not RS.BOF Response.Write RS("firstName") & " " & RS("lastName") & "<br>" RS.MovePrevious Loop

Adovbs.inc So far we have defined the constants for the cursor types ourselves These are actually in a file called adovbs.inc You can include this in your scripts <!--#include virtual=“adovbs.inc”--> <!--#include file=“adovbs.inc”-->

Counting Records How do you determine the number of records in a RecordSet? Have a loop Move through the RecordSet and count them Use the RecordCount property of a scrollable cursor Response.Write "The number of names is " & RS.RecordCount & "<br>"

Locking When two people try to update a record at the same time, confusion and errors result To avoid this problem, VBScript can be configured to lock the records This means that one person locks the record and updates it The other person cannot read or update the record until the first person releases their lock

Lock Types Lock Constant Description Read-only adLockReadOnly Records are read-only and cannot be modified or added. Default lock type. Pessimistic adLockPessimistic Records are locked as soon as editing begins. Optimistic adLockOptimistic Locks row only when update is called. Used when having multiple users making changes to the same records is not a major concern. Batch optimistic adLockBatchOptimistic Outside course scope

Syntax for Opening Record Sets Open a Scrollable, updatable Recordset with parameters sql = “Select * from students” Rs.open sql, conn, adOpenStatic, adLockOptimistic, adCmdText Open a RecordSet after setting the properties Set rs = Server.CreateObject("ADODB.RecordSet") rs.LockType = adLockOptimistic rs.CursorType = adOpenStatic rs.Open sql, conn * adCmdText – indicates that the source holds command text, such as an SQL command

Adding Records If you call RS.AddNew It will create a new, blank record and make it the current record You can then assign values to the fields Finally, call RS.Update to write the changes to the DB

Adding Records RS.AddNew RS(“firstName”) = “Fred” RS(“lastName”) = “Flintstone” RS.Update

Updating Records To update an existing record Get the record from the database Modify the field(s) Call Update or CancelUpdate RS(“firstName”) = “Frederick” RS.Update

Deleting Records You can delete an existing record by Find the record you want to delete (sql query) Call RS.Delete RS.MoveFirst RS.Delete