BeginTrans, CommitTrans et RollbackTrans, méthodes – Exemple (VJ++)

S’applique à : Access 2013, Office 2013

Cet exemple montre comment modifier le type de livre de tous les livres de psychologie dans la table Titres de la base de données. Une fois que la méthode BeginTrans a démarré une transaction qui isole toutes les modifications apportées à la table Titles , la méthode CommitTrans enregistre les modifications. You can use the Rollback method to undo changes that you saved using the Update method.

 
// BeginBeginTransJ 
import com.ms.wfc.data.*; 
import java.io.*; 
 
public class BeginTransX 
{ 
 // The main entry point for the application. 
 
 public static void main (String[] args) 
 { 
 BeginTransX(); 
 System.exit(0); 
 } 
 
 // BeginTransX function 
 static void BeginTransX() 
 { 
 // Define ADO Objects. 
 Connection cnConn1 = null; 
 Recordset rstTitles = null; 
 
 //Declarations. 
 String strCnn = "Provider='sqloledb';Data Source='MySqlServer';" 
 + "Initial Catalog='Pubs';Integrated Security='SSPI';"; 
 String strTitle; 
 String strType; 
 BufferedReader in = 
 new BufferedReader (new InputStreamReader (System.in)); 
 String line = null; 
 String strMessage=""; 
 int intChoice = 0; 
 int recordDisplaySize = 15; 
 int recordCount = 0; 
 
 try 
 { 
 // Open a connection. 
 
 cnConn1 = new Connection(); 
 cnConn1.open(strCnn,"","",AdoEnums.CommandType.UNSPECIFIED); 
 
 // Open the Titles table. 
 rstTitles = new Recordset (); 
 rstTitles.setCursorType(AdoEnums.CursorType.DYNAMIC); 
 rstTitles.setLockType(AdoEnums.LockType.PESSIMISTIC); 
 rstTitles.open("titles",cnConn1,AdoEnums.CursorType.DYNAMIC , 
 AdoEnums.LockType.PESSIMISTIC ,AdoEnums.CommandType.TABLE ); 
 
 rstTitles.moveFirst(); 
 cnConn1.beginTrans(); 
 
 // Loop through recordset and ask user if he/she wants 
 // to change the type for a specified title. 
 
 while (!rstTitles.getEOF()) 
 { 
 strType = rstTitles.getField("type").getString().trim(); 
 if ((rstTitles.getField("type").getString(). 
 trim()).compareTo("psychology")== 0) 
 { 
 strTitle = rstTitles.getField("title").getString().trim(); 
 System.out.println("\nTitle : " + strTitle + "\n\n" 
 + "Change type to self help (1 -> Yes / 2 -> No) ?"); 
 // Change the title for the specified book. 
 line = in.readLine().trim(); 
 intChoice = Integer.parseInt(line); 
 if ( intChoice == 1) 
 { 
 rstTitles.getField("type").setString("self_help"); 
 rstTitles.update(); 
 } 
 } 
 rstTitles.moveNext(); 
 } 
 
 // Ask if the user wants to commit to all the 
 // changes made above. 
 System.out.println 
 ("\n\nSave all changes (1 -> Yes / 2 -> No) ?"); 
 line = in.readLine().trim(); 
 intChoice = Integer.parseInt(line); 
 if ( intChoice == 1) 
 cnConn1.commitTrans(); 
 else 
 cnConn1.rollbackTrans(); 
 
 // Print current data in recordset. 
 rstTitles.requery(); 
 rstTitles.moveFirst(); 
 
 while(true) 
 { 
 strMessage = strMessage +"\n " + 
 rstTitles.getField("title").getString()+" - " 
 + rstTitles.getField("type").getString() ; 
 
 if ( recordCount == recordDisplaySize) 
 { 
 System.out.println(strMessage); 
 System.out.println("\n\nPress <Enter> key to continue.."); 
 line = in.readLine(); 
 strMessage = ""; 
 recordCount = 0; 
 } 
 recordCount++; 
 rstTitles.moveNext(); 
 if(rstTitles.getEOF()) 
 { 
 System.out.println(strMessage); 
 break; 
 } 
 } 
 System.out.println("\n\nPress <Enter> key to continue.."); 
 line = in.readLine(); 
 
 // Restore original data because this 
 // is a demonstration. 
 rstTitles.moveFirst(); 
 while (!rstTitles.getEOF()) 
 { 
 if ((rstTitles.getField("type").getString(). 
 trim().compareTo("self_help"))== 0) 
 { 
 rstTitles.getField("type").setString("psychology"); 
 rstTitles.update(); 
 } 
 rstTitles.moveNext(); 
 } 
 } 
 catch( AdoException ae ) 
 { 
 // Notify user of any errors that result from ADO. 
 
 // Check for null pointer for connection object. 
 if(rstTitles.getActiveConnection()==null) 
 System.out.println("Exception: " + ae.getMessage()); 
 
 // As passing a Recordset, check for null pointer first. 
 if (rstTitles != null) 
 { 
 PrintProviderError(rstTitles.getActiveConnection()); 
 } 
 else 
 { 
 System.out.println("Exception: " + ae.getMessage()); 
 } 
 } 
 // System Read requires this catch. 
 catch( java.io.IOException je ) 
 { 
 PrintIOError(je); 
 } 
 finally 
 { 
 // Cleanup objects before exit. 
 if (rstTitles != null) 
 if (rstTitles.getState() == 1) 
 rstTitles.close(); 
 if (cnConn1 != null) 
 if (cnConn1.getState() == 1) 
 cnConn1.close(); 
 } 
 } 
 
 // PrintProviderError Function 
 
 static void PrintProviderError( Connection Cnn1 ) 
 { 
 // Print Provider errors from Connection object. 
 // ErrItem is an item object in the Connections Errors collection. 
 com.ms.wfc.data.Error ErrItem = null; 
 long nCount = 0; 
 int i = 0; 
 
 nCount = Cnn1.getErrors().getCount(); 
 
 // If there are any errors in the collection, print them. 
 if( nCount > 0); 
 { 
 // Collection ranges from 0 to nCount - 1 
 for (i = 0; i< nCount; i++) 
 { 
 ErrItem = Cnn1.getErrors().getItem(i); 
 System.out.println("\t Error number: " + ErrItem.getNumber() 
 + "\t" + ErrItem.getDescription() ); 
 } 
 } 
 
 } 
 
 //.PrintIOError Function 
 
 static void PrintIOError( java.io.IOException je) 
 { 
 System.out.println("Error \n"); 
 System.out.println("\tSource = " + je.getClass() + "\n"); 
 System.out.println("\tDescription = " + je.getMessage() + "\n"); 
 } 
} 
 
// EndBeginTransJ