Why do we need Persistent Classes ?
Dear OO Gurus,
I just finished the chapter on "Persistent Objects" in "ABAP Objects - ABAP Programming in SAP NW by Horst Keller".
I could really appreciate its utility though. Googled a bit, read a few blogs on SCN but still the utility remains blurred.
I would like to know what is the advantage of Persistence Classes over Open SQL.
BR,
Suhas
I would like to know what is the advantage of Persistence Classes over Open SQL.
Let's first start with what SAP says about the [persistence service|http://help.sap.com/saphelp_nw70ehp2/helpdata/en/f5/a36828bc6911d4b2e80050dadfb92b/frameset.htm]:
The Persistence Service lets the ABAP programmer work with relational database data in an object-oriented way.
So we're talking here about an [ORM|http://en.wikipedia.org/wiki/Object-relational_mapping] framework. I.e. the persistent storage of data is realized in SAP via a [relational database|http://en.wikipedia.org/wiki/Relational_database], where the data model is not object oriented. Let's say that you have created a class sales order and want to store and retrieve sales order objects (i.e. specific instances of this class). If you have a relational database, you have to model a corresponding schema for representing your sales order class and then "handcode" the translation from database tables into sales order objects and vice versa.
Now imagine a world where you have a nice ORM, that does the work for you. E.g. look at web frameworks like [grails|http://www.grails.org/] making heavy use of [convention over configuration|http://en.wikipedia.org/wiki/Convention_over_configuration], which allow you to easily generate database representations from your objects (without tons of coding/effort!). Essentially you can start off with your class definitions, define some attributes and the framework (ORM) will automatically generate the corresponding database tables for you.
Contrast that with SAP (see online help on [mapping assistant for persistence classes|http://help.sap.com/saphelp_nw70ehp2/helpdata/en/d9/b84508bc9411d4b2e80050dadfb92b/frameset.htm]):
You may have to create new database tables, database views, or structures for the object model in the ABAP Dictionary. At present the system does not perform this function automatically.
So in general the ORM is supposed to make the developer's life easier by providing a framework for translating objects into (relational) database tables. However, sometimes the automatic translation/generation along with the default access methods is not optimal and that's where you actually go back to code your own SQL statements for doing the database-to-object conversions and vice versa. So the SAP persistence classes still use OpenSQL under the hood, but in some cases (e.g. mass processing), you might want to tune the used SQL statements yourself...
I apologize for the long excursion, but in the end my view on persistence classes is quite simple: Use them if they make your life more simple and your coding less complex, without causing any bigger performance hit - otherwise stick to handcoded SQL statements... (long live [KISS|http://en.wikipedia.org/wiki/KISS_principle]!)
Cheers, harald
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import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.text.*;
import javax.xml.parsers.*;
import org.xml.sax.*;
import java.io.*;
import org.w3c.dom.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.*;
import javax.xml.transform.stream.*;
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int MonthLength [] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
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private JLabel lbl, reminderlbl;
private JPanel top, grid, remindercenter, reminderbottom;
private JFrame reminderframe;
private JTextField year1, reminderinput, dayno;
private JComboBox months;
private Container container;
private JButton fetch, save, cancel;
private Document doc;
private File file;
private Node node;
private String year, month, day;
public static void main( String[] args ) {
CalendarAssignment c = new CalendarAssignment( );
c.setSize( 400, 300 );
c.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
c.show( );
public CalendarAssignment( ) {
int CurrentYear, CurrentMonth;
String YearString, MonthString, Now;
Date today;
container = getContentPane( );
container.setLayout( new BorderLayout( ) );
SimpleDateFormat DateFormatter;
DateFormatter = new SimpleDateFormat( "MM.yyyy" );
today = new Date( );
Now = DateFormatter.format( today );
MonthString = Now.substring( 0,2 );
YearString = Now.substring( 3,7 );
CurrentMonth = Integer.valueOf( MonthString );
CurrentYear = Integer.valueOf( YearString );
top = new JPanel( );
String [] items = { "January", "February", "March", "April", "May", "June",
"July", "August", "September", "October", "November",
"December" };
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year1.setText( YearString );
year1.setEditable( true );
year1.setHorizontalAlignment( year1.CENTER );
fetch = new JButton( "Fetch Month" );
fetch.addActionListener( this );
top.setLayout( new GridLayout( 1, 3, 20, 0 ) );
top.add( months );
top.add( year1 );
top.add( fetch );
grid = new JPanel( );
grid.setLayout( new GridLayout( 7, 7, 0, 0 ) );
String [] week = { "Mon", "Tue", "Wed", "Thur", "Fri", "Sat", "Sun" };
for ( int a = 0; a < 7; a ++ ) {
JLabel lbl = new JLabel( week[a], JLabel.CENTER );
grid.add( lbl );
for ( int i = 0; i < 42; i ++ ) {
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container.add( top, BorderLayout.NORTH );
container.add( grid, BorderLayout.CENTER );
private void DrawCalendar( int SelectMonth, int SelectYear ) {
int DisplayMonthLength, Buttons;
String ButtonID = "";
int OffSet = MonthStart( SelectMonth, SelectYear );
DisplayMonthLength = MonthLength [SelectMonth - 1];
if ( SelectMonth == 2 )
DisplayMonthLength += LeapYear( SelectYear );
for ( Buttons = 1; Buttons < 43; Buttons ++ ) {
if ( ( Buttons <= OffSet ) || ( Buttons > ( DisplayMonthLength + OffSet ) ) ) {
ButtonID = "";
days[Buttons-1].setEnabled( false );
else {
ButtonID = Integer.toString( Buttons - OffSet );
days[Buttons-1].setEnabled( true );
days[Buttons-1].setLabel( ButtonID );
grid.add( days[Buttons-1] );
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int FourHundred, OneHundred, Fourth;
FourHundred = year % 400;
OneHundred = year % 100;
Fourth = year % 4;
if( ( ( FourHundred == 0 ) ) || ( ( OneHundred != 0 ) && ( Fourth == 0 ) ) )
return ( 1 );
else
return ( 0 );
private int MonthStart( int Month, int Year ) {
int OffSet, LastMonths, BeforeOrAfter, Years;
int AllDays = 0;
int YearDays = 365;
int YearMonths = 12;
BeforeOrAfter = Year - 2006;
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if( BeforeOrAfter != 0 )
BeforeOrAfter = BeforeOrAfter / Years;
switch( BeforeOrAfter ) {
case 1:
for( int a = 2006; a < Year; a ++ ) {
AllDays += YearDays + LeapYear( a );
AllDays += LastMonthsCalc( Month, Year );
break;
case -1:
for( int a = 2005; a > Year; a -- ) {
AllDays += YearDays + LeapYear( a );
for( LastMonths = YearMonths; LastMonths >= Month; LastMonths -- ) {
AllDays += MonthLength[LastMonths - 1];
if( LastMonths == 2 )
AllDays += LeapYear( Year );
break;
default:
if( Month > 1 )
AllDays += ( LastMonthsCalc( Month, Year ) );
OffSet = AllDays % 7;
if( BeforeOrAfter ==( -1 ) )
return( 6 - OffSet );
else if( OffSet > 0 )
return( OffSet - 1 );
else
return( 6 );
private int LastMonthsCalc( int Month, int Year ) {
int Counter;
int days = 0;
for( Counter = 1; Counter < Month; Counter ++ ) {
days += MonthLength[Counter - 1];
if( Counter == 2 )
days += LeapYear( Year );
return( days );
public void CreateReminder( String buttonID, String yearID, String monthID ) {
reminderframe = new JFrame( );
reminderlbl = new JLabel( );
reminderframe.setLayout( new GridLayout( 2, 1, 0, 0 ) );
remindercenter = new JPanel( );
reminderlbl = new JLabel( "Please type in reminder to be saved for " + buttonID + " " + monthID + " " + yearID + ":", JLabel.CENTER );
reminderinput = new JTextField( 30 );
reminderinput.setHorizontalAlignment( reminderinput.CENTER );
reminderinput.setEditable( true );
remindercenter.setLayout( new GridLayout( 2, 1, 0, 0 ) );
remindercenter.add( reminderlbl );
remindercenter.add( reminderinput );
reminderbottom = new JPanel( );
save = new JButton( "Save" );
save.addActionListener( this );
cancel = new JButton( "Cancel" );
cancel.addActionListener( this );
dayno = new JTextField( buttonID );
dayno.setEditable( false );
dayno.setEnabled( false );
dayno.show( false );
reminderbottom.setLayout( new FlowLayout( ) );
reminderbottom.add( save );
reminderbottom.add( cancel );
reminderbottom.add( dayno );
reminderframe.setSize( 500, 75 );
reminderframe.add( remindercenter );
reminderframe.add( reminderbottom );
reminderframe.pack( );
reminderframe.show( );
public void SaveReminder( String dayID, String yearID, String monthID ) throws Exception {
file = new File( "Diary.xml" );
doc = DocumentBuilderFactory.newInstance( ).newDocumentBuilder( ).parse( file.toURL( ).toString( ) );
String year = yearID;
String month = monthID;
String day = dayID;
//System.out.println( year );
//System.out.println( month );
//System.out.println( day );
CreateEntry( doc.getDocumentElement( ) );
writeXmlFile( );
public boolean CreateEntry( Node node ) {
Node searchNode;
searchNode = getYear( node );
if( searchNode == null ) {
Element newNode = doc.createElement( "Year" );
searchNode = node.appendChild( newNode );
newNode.setAttribute( "Id", year );
node = searchNode;
searchNode = getMonth( node );
if( searchNode == null ) {
Element newNode = doc.createElement( "Month" );
searchNode = node.appendChild( newNode );
newNode.setAttribute( "Id", month );
node = searchNode;
searchNode = getDay( node );
if( searchNode == null ) {
Element newNode = doc.createElement( "Day" );
searchNode = node.appendChild( newNode );
newNode.setAttribute( "Id", day );
node = searchNode;
String entry = reminderinput.getText( );
Node textNode = doc.createTextNode( entry );
node.appendChild( textNode );
return true;
private Node getYear( Node node ) {
node = node.getFirstChild( );
while( node != null ) {
if(node.getNodeName( ).equals( "Year" ) && String.valueOf( node.getAttributes( ).item( 0 ).getNodeValue( ) ) == year )
return node;
node = node.getNextSibling( );
return null;
private Node getMonth( Node node ) {
node = node.getFirstChild( );
while( node != null ) {
if( node.getNodeName( ).equals( "Month" ) && String.valueOf( node.getAttributes( ).item( 0 ).getNodeValue( ) ) == month )
return node;
node = node.getNextSibling( );
return null;
private Node getDay( Node node ) {
node = node.getFirstChild( );
while( node != null ) {
if( node.getNodeName( ).equals( "Day" ) && String.valueOf( node.getAttributes( ).item( 0 ).getNodeValue( ) ) == day )
return node;
node = node.getNextSibling( );
return null;
private void writeXmlFile( ) throws Exception {
Source source = new DOMSource( doc );
Result result = new StreamResult( file );
Transformer xformer = TransformerFactory.newInstance( ).newTransformer( );
xformer.setOutputProperty( OutputKeys.INDENT,"yes" );
xformer.setOutputProperty( OutputKeys.DOCTYPE_SYSTEM,"Diary.dtd" );
xformer.transform( source, result );
public void actionPerformed( ActionEvent e ) {
String IDButton = e.getActionCommand( );
String IDYear = year1.getText( );
Object IDMonthObj = months.getSelectedItem( );
if( e.getSource( ) == fetch ) {
String YearText = year1.getText( );
int YearNumber = Integer.valueOf( YearText );
int MonthsIndex = months.getSelectedIndex( ) + 1;
DrawCalendar( MonthsIndex, YearNumber );
else if( e.getSource( ) == cancel ) {
reminderframe.hide( );
else if( e.getSource( ) == save ) {
String IDDay = dayno.getText( );
String IDMonth = String.valueOf( IDMonthObj );
SaveReminder( IDDay, IDYear, IDMonth );
else {
String IDMonth = String.valueOf( IDMonthObj );
Toolkit.getDefaultToolkit( ).beep( );
int n = JOptionPane.showConfirmDialog( null, "Set reminder on this date?", "Question", JOptionPane.YES_NO_OPTION );
if( n == JOptionPane.YES_OPTION ) {
CreateReminder( IDButton, IDYear, IDMonth );
If you compile it, you will realise that I get an error about exception handling. My lecturer gave me an example code of how to do the same thing without using a GUI:
import javax.xml.parsers.*;
import org.xml.sax.*;
import java.io.*;
import java.util.*;
import org.w3c.dom.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.*;
import javax.xml.transform.stream.*;
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Document doc;
File file;
Scanner input;
int year, month, day;
String currentYear, currentMonth;
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CallDOM() throws Exception
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System.out.println("2) Read entry");
System.out.println("3) Show Diary");
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writeXmlFile();
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month=input.nextInt();
year=input.nextInt();
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node = searchNode;
searchNode = getMonth(node);
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node = searchNode;
System.out.println("Enter Text");
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entry+=input.nextLine();
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node.appendChild(textNode);
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node = stack.pop();
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child = node.getLastChild();
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currentYear=node.getAttributes().item(0).getNodeValue();
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currentMonth=node.getAttributes().item(0).getNodeValue();
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currentMonth+"/"+currentYear+": ");
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node=node.getFirstChild();
while(node!=null)
if(node.getNodeName().equals("Year")
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return node;
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}My question is, why does the exceptions in the example code not need to be caught? And why do I have to catch the exceptions in my code? Several exceptions are thrown in the example code, but there is no catch statement.
Thanks for any advice!!Since your question didn't come with any relevant details, and since you have huge steaming piles of irrelevant code, all I can give is a general answer to "Why do I need to catch this exception?"
[url http://java.sun.com/docs/books/tutorial/essential/exceptions/index.html]Exception tutorial at http://java.sun.com/docs/books/tutorial/essential/exceptions/index.html
Here's a quick overview of exceptions:
The base class for all exceptions is Throwable. Java provides Exception and Error that extend Throwable. RuntimeException (and many others) extend Exception.
RuntimeException and its descendants, and Error and its descendants, are called unchecked exceptions. Everything else is a checked exception.
If your method, or any method it calls, can throw a checked exception, then your method must either catch that exception, or declare that your method throws that exception. This way, when I call your method, I know at compile time what can possibly go wrong and I can decide whether to handle it or just bubble it up to my caller. Catching a given exception also catches all that exception's descendants. Declaring that you throw a given exception means that you might throw that exception or any of its descendants.
Unchecked exceptions (RuntimeException, Error, and their descendants) are not subject to those restrictions. Any method can throw any unchecked exception at any time without declaring it. This is because unchecked exceptions are either the sign of a coding error (RuntimeException), which is totally preventable and should be fixed rather than handled by the code that encounters it, or a problem in the VM, which in general can not be predicted or handled. -
Problem in creating a Persistent Class
Hi All,
I am working on Persistent Classes for the first time. I have tried to gain some info by going through some related threads and of course Thomas' Blog on Persistent Classes.
My Problem:
I have been trying to create a Persistent Class that takes fields from multiple database tables (KNA1 and KNVV).
I wasn't able to generate mapping successfully.
So, the solution was to create 2 Persistent Classes and create a data model class for these two (It was mentioned in one of the threads)
I have been trying to create a Persistent Class for the fields from table KNA1 (I need only some 11 fields)
When I activate, I again get a warning 'No mapping exists for the fields' as a result of which the main class is not activated.
I read somewhere that all fields from a table needs to be included in the 'Inclusion area', otherwise, the class doesn't activate.
So I tried creating a view, but I get another warning message saying 'Database operations with view are not allowed' and the main class remains unactivated.
Please suggest.
Also, if there are any related materials on how to deal with multiple tables, I would be more than glad.
Thanks for all your time.If you are creating a persistent class for SAP tables, then effectively you are attempting to update the tables directly. And that is a really bad idea.
See [here|regarding updation of database table...; and [here |Important points to be cautios of when updating a standard table; for more discussion on that topic.
Only create persistent classes for database operations on your own tables.
I guess your classes are failing because you haven't done the mapping. Did you click on the button marked "persistence" on the SE24 view of your ZCL class?
matt
One more thing - it's against the forum rules to ask for material and links... -
What am I doing wrong with the isNew() method? and why do I need the other methods?
I have coded an include jsp like this.
<%@page language="Java"%>
<%@page import="javax.servlet.http.HttpSession"%>
<%!
String iContextPath;
String iCommonPath;
String iImagesPath;
%>
<%
iContextPath = request.getContextPath();
iCommonPath = iContextPath + "/common";
iImagesPath = iCommonPath + "/images";
System.err.println(" here ");
HttpSession thisSession = request.getSession( false );
if( thisSession.isNew() ){
System.err.println("isnew");
response.sendRedirect( iContextPath + "/common/login.jsp" );
%>
Now I also have a redirect.jsp in the root of an application that contains
this.
<html>
<body>
<%
System.err.println("Redirecting at this time from the root");
response.sendRedirect( request.getContextPath() + "/secureArea/");
%>
</body>
</html>
And I have a logout.java servlet that looks like this.
package com.pch.epics;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import weblogic.servlet.security.ServletAuthentication;
public class Logout extends HttpServlet{
private static final String CONTENT_TYPE = "text/html";
//Initialize global variables
public void init() throws ServletException{
//Process the HTTP Get request
public void doGet( HttpServletRequest request, HttpServletResponse
response ) throws ServletException, IOException{
String username = "";
if( request.getUserPrincipal() == null ){
username = "Unknown";
} else {
username = request.getUserPrincipal().getName();
System.err.println( "ePics logging out '" + username + "'" );
request.getSession( false ).invalidate();
ServletAuthentication.logout( request );
ServletAuthentication.invalidateAll( request );
ServletAuthentication.killCookie( request );
response.sendRedirect( request.getContextPath() );
//Process the HTTP Post request
public void doPost( HttpServletRequest request, HttpServletResponse
response ) throws ServletException, IOException{
doGet( request, response );
//Clean up resources
public void destroy(){
First of all, why won't the isNew() report a new session in the server log?
EVERY request coming in says it's an old request (ie it's not new). The
J2EE Applications and BEA WebLogic Server book from BEA says this should
work.
My second question is why do I need to do those three lines from
ServletAuthentication to logout a user? Ok, maybe I'm from the MS world,
but that seems excessive, especially since I've already done a
session.invalidate() right before it, but the bea docs say I'm required to
do all four!
When you invalidate a session. You invalidate the session of the web
application that your jsp/servlet is part of. It is possible to have more
than one web application on WLS and have them share a authentication info.
While these applications share authentication they do not share their
sessions so because of that calling session invalidate does not kill all the
sessions. ServletAuthentication is needed to kill all the sessions and do a
complete logout from WLS.
"Flip" <[remove][email protected]> wrote in message
news:[email protected]...
> I have coded an include jsp like this.
>
> <%@page language="Java"%>
> <%@page import="javax.servlet.http.HttpSession"%>
> <%!
> String iContextPath;
> String iCommonPath;
> String iImagesPath;
> %>
> <%
> iContextPath = request.getContextPath();
> iCommonPath = iContextPath + "/common";
> iImagesPath = iCommonPath + "/images";
>
> System.err.println(" here ");
> HttpSession thisSession = request.getSession( false );
> if( thisSession.isNew() ){
> System.err.println("isnew");
> response.sendRedirect( iContextPath + "/common/login.jsp" );
> }
>
> %>
>
> Now I also have a redirect.jsp in the root of an application that contains
> this.
> <html>
> <body>
> <%
> System.err.println("Redirecting at this time from the root");
> response.sendRedirect( request.getContextPath() + "/secureArea/");
> %>
> </body>
> </html>
>
> And I have a logout.java servlet that looks like this.
> package com.pch.epics;
>
> import java.io.IOException;
> import javax.servlet.ServletException;
> import javax.servlet.http.HttpServlet;
> import javax.servlet.http.HttpServletRequest;
> import javax.servlet.http.HttpServletResponse;
> import weblogic.servlet.security.ServletAuthentication;
>
> public class Logout extends HttpServlet{
> private static final String CONTENT_TYPE = "text/html";
> //Initialize global variables
> public void init() throws ServletException{
> }
>
> //Process the HTTP Get request
> public void doGet( HttpServletRequest request, HttpServletResponse
> response ) throws ServletException, IOException{
> String username = "";
> if( request.getUserPrincipal() == null ){
> username = "Unknown";
> } else {
> username = request.getUserPrincipal().getName();
> }
> System.err.println( "ePics logging out '" + username + "'" );
> request.getSession( false ).invalidate();
> ServletAuthentication.logout( request );
> ServletAuthentication.invalidateAll( request );
> ServletAuthentication.killCookie( request );
> response.sendRedirect( request.getContextPath() );
> }
>
> //Process the HTTP Post request
> public void doPost( HttpServletRequest request, HttpServletResponse
> response ) throws ServletException, IOException{
> doGet( request, response );
> }
>
> //Clean up resources
> public void destroy(){
> }
> }
>
> First of all, why won't the isNew() report a new session in the server
log?
> EVERY request coming in says it's an old request (ie it's not new). The
> J2EE Applications and BEA WebLogic Server book from BEA says this should
> work.
>
> My second question is why do I need to do those three lines from
> ServletAuthentication to logout a user? Ok, maybe I'm from the MS world,
> but that seems excessive, especially since I've already done a
> session.invalidate() right before it, but the bea docs say I'm required to
> do all four!
>
>
>
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