Re: [OJB-developers] Re: Named Root Objects

[Michael N. <mic...@gm...>]

Hi Thomas!

Is there a way to let OJB create and remove tables automatically. In my
opinion such a feature could come in quite handy while developing your app.
JBoss has such an option. An XSLT Stylesheet that transforms
the repository XML into sql statements could look like this:

<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
  <xsl:output method="text" omit-xml-declaration="yes" indent="yes"/>

  <xsl:template match="/">
    <xsl:for-each select="MappingRepository/ClassDescriptor">
    <!-- generate sql drop table statement-->
    <xsl:text>drop table </xsl:text><xsl:value-of
select="table.name"/><xsl:text>;
    </xsl:text>
    <!-- generate sql create table statement-->
    <xsl:text>create table </xsl:text><xsl:value-of
select="table.name"/><xsl:text> (
    </xsl:text>
      <xsl:for-each select="FieldDescriptor">
        <xsl:value-of select="column.name"/>
        <xsl:text> </xsl:text>
        <xsl:value-of select="jdbc_type"/>
   <xsl:if test="PrimaryKey='true'">
     <xsl:text> NOT NULL PRIMARY KEY</xsl:text>
   </xsl:if>
        <xsl:text>
        </xsl:text>
      </xsl:for-each>
    <xsl:text>);

    </xsl:text>
    </xsl:for-each>
  </xsl:template>
</xsl:stylesheet>

What still remains to be done is inserting switches that indicate whether
you want automatic table creation/removal enabled or not. It might be
possible to change
the repository.dtd accordingly.
Another thing I don't know is whether jdbc types are automatically mapped to
sql types by the jdbc driver.

Greetings, Michael
----- Original Message -----
From: "Mahler Thomas" <tho...@it...>
To: "'Michael Nowotny'" <mic...@gm...>; "ojb"
<obj...@li...>
Sent: Tuesday, January 15, 2002 10:29 AM
Subject: AW: [OJB-developers] Re: Named Root Objects


> Hi Michael,
>
>
> There will be a lot of people using OJB who do not use named roots.
> Just imagine their faces when the GC starts and deletes all their objects
> because they where unreferenced >:-() !!!
>
> Thus Having the GC as a separate tool is a good idea, not to say a MUST!
>
> Implementing a GC that will reclaim everything that can not be reached
from
> a named root will not be difficult.
> The algorithm you describe is a simple "mark and sweep" algorithm. Would
be
> fun to implement such a thing!
>
> cheers,
>
> Thomas
>
>
> >
> > Hi Thomas!
> >
> > I've been thinking about the GC process over the last few days.
> >
> > > Currently there is no GC implemented.
> > > IMHO it will be VERY difficult to have a real GC as it
> > would be possible
> > > with an OODBMS.
> > > It will be very difficult to decide if objects can safely
> > be deleted.
> > >
> > > BUT: we have been thinking of changing the semantics of
> > DList.remove()
> > > an similar methods as name roots unbind so that removed objects are
> > > deleted from the DB.
> >
> > A first step towards true persistence by reachability could
> > be to offer
> > offline GC. This way you don't have the to deal with objects which not
> > reachable from any named root object any more but are still
> > referenced under
> > another transaction that has not yet committed. The algorithm
> > could look
> > like this:
> >
> > 1. Make a list of all objects stored in the database
> > 2. from every named root object traverse the object graph and mark any
> > object you come across as being persistent
> > 3. delete all the objects from the database which are
> > currently not marked
> > as persistent.
> >
> > The algorithm can be implemented using recursion. In order to avoid
> > indefinite loops caused by cyclic references, the algorithm
> > has to check
> > whether an object under investigation is already marked.
> >
> > Another advantage is that people who do not want seamless
> > persistence the
> > "Java Way" but instead want to have a more basic level
> > control over their
> > data still have the option not to execute the garbage collector.
> >
> > What do you think about it?
> >
>
>
> > Greetings Michael
> > ----- Original Message -----
> > From: "Thomas Mahler" <tho...@ho...>
> > To: "Michael Nowotny" <mic...@gm...>; "ojb"
> > <obj...@li...>
> > Sent: Wednesday, January 09, 2002 6:51 PM
> > Subject: Re: Named Root Objects
> >
> >
> > > Hi again,
> > >
> > >
> > > Michael Nowotny wrote:
> > >
> > > > Hi Thomas!
> > > >
> > > > Thanks for the illustration. Binding collections works
> > fine for me now!
> > > > The reason why my earlier attempt failed was that I was
> > still using
> > > > InstantDB.It seems that some transactions got only
> > halfway commited due
> > to
> > > > program termination following db.close(). Now I'm using
> > Hypersonic and
> > > > everything works.
> > > >
> > >
> > > Fine !
> > >
> > >
> > > > During the course of setting up a test procedure I came
> > across some
> > strange
> > > > behaviour. The following code snipped throws an
> > ObjectNameNotBoundException.
> > > >
> > > >             // fails:
> > > >             tx = odmg.newTransaction();
> > > >             tx.begin();
> > > >             db.bind(odmg.newDList(), "MyList");
> > > >             db.unbind("MyList");
> > > >             db.bind(odmg.newDList(), "MyList");
> > > > //            DList list = (DList)db.lookup("MyList");
> > > >             tx.commit();
> > > >
> > > >             tx = odmg.newTransaction();
> > > >             tx.begin();
> > > >             DList newList = (DList)db.lookup("MyList");
> > > >             tx.commit();
> > > >
> > > > Binding the same name twice within the same transaction
> > seems to cause
> > an
> > > > error.
> > >
> > >
> > > Oops, This is a bug. I'll add it to my todo list!
> > >
> > >
> > > This is not very important though because usually one wouldn't want
> > > > to bind an object to a some name and thereafter unbinding
> > that name
> > withing
> > > > the same transaction.
> > > >
> > > > Another question arose when I had a look at the contents
> > of my database.
> > If
> > > > I add content to my list which is a named root object
> > this content gets
> > > > persistent as well. That's part of persistence by
> > reachability. But when
> > I
> > > > unbind the root object and the content is therefore no
> > longer reachable,
> > it
> > > > doesn't get removed from the database but is still
> > present. Is there any
> > way
> > > > of performing some kind of garbage collection?
> > > >
> > >
> > >
> > >
> > > Currently there is no GC implemented.
> > > IMHO it will be VERY difficult to have a real GC as it
> > would be possible
> > > with an OODBMS.
> > > It will be very difficult to decide if objects can safely
> > be deleted.
> > >
> > > BUT: we have been thinking of changing the semantics of
> > DList.remove()
> > > an similar methods as name roots unbind so that removed objects are
> > > deleted from the DB.
> > >
> > > Any ideas?
> > >
> > > -- Thomas
> > >
> > >
> > >
> > >
> > > > Keep up the good work!
> > > >
> > > > Thanks, Michael
> > > >
> > > > ----- Original Message -----
> > > > From: "Thomas Mahler" <tho...@ho...>
> > > > To: "Michael Nowotny" <mic...@gm...>; "ojb"
> > > > <obj...@li...>
> > > > Sent: Tuesday, January 08, 2002 8:20 PM
> > > > Subject: Re: Named Root Objects
> > > >
> > > >
> > > >
> > > >>Hi Michael,
> > > >>
> > > >>please see the attached Java class.
> > > >>
> > > >>You can replace the original version of
> > test.ojb.odmg.OdmgExamples with
> > > >>this new version to have it executed with the OJB JUnit tests.
> > > >>
> > > >>There is a new testMethod testNrmAndDlists that tests
> > your scenario.
> > > >>Works great!
> > > >>
> > > >>HTH,
> > > >>
> > > >>Thomas
> > > >>
> > > >>Michael Nowotny wrote:
> > > >>
> > > >>
> > > >>>Hi Thomas!
> > > >>>
> > > >>>Just found your OJB project on sourceforge. I think it's
> > great to have
> > > >>>
> > > > an
> > > >
> > > >>>open source ODMG implementation around.
> > > >>>Now I've got a question concerning the ODMG implemetation.
> > > >>>Is it possible to use a DList for example as a named root object.
> > > >>>
> > > > Binding
> > > >
> > > >>>that object to a name works but looking it up again causes an
> > > >>>IllegalArgumentException.
> > > >>>
> > > >>>Have you ever tried to bind a Collection. If so, I would
> > be grateful if
> > > >>>
> > > > you
> > > >
> > > >>>could drop me some lines of source code.
> > > >>>
> > > >>>Thanks Michael
> > > >>>
> > > >>>
> > > >>>
> > > >>>
> > > >>>
> > > >>>
> > > >>
> > > >>
> > > >
> > > >
> > >
> > >
> > --------------------------------------------------------------
> > ------------
> > --
> > > > ----
> > > >
> > > >
> > > >
> > > >>package test.ojb.odmg;
> > > >>
> > > >>
> > > >>import junit.framework.TestCase;
> > > >>import ojb.broker.Identity;
> > > >>import ojb.broker.PersistenceBroker;
> > > >>import ojb.broker.PersistenceBrokerFactory;
> > > >>import ojb.broker.cache.ObjectCacheFactory;
> > > >>import ojb.odmg.OJB;
> > > >>import ojb.odmg.states.ModificationState;
> > > >>import ojb.odmg.states.StateNewClean;
> > > >>import ojb.odmg.states.StateNewDirty;
> > > >>import org.odmg.*;
> > > >>
> > > >>import java.util.List;
> > > >>
> > > >>/** Demo Application that shows basic concepts for
> > Applications using
> > the
> > > >>
> > > > OJB ODMG
> > > >
> > > >> * implementation as an transactional object server.
> > > >> */
> > > >>public class OdmgExamples extends TestCase
> > > >>{
> > > >>    public static void main(String[] args)
> > > >>    {
> > > >>        String[] arr = {CLASS.getName()};
> > > >>        junit.textui.TestRunner.main(arr);
> > > >>    }
> > > >>
> > > >>    private static Class CLASS = OdmgExamples.class;
> > > >>    private String databaseName;
> > > >>
> > > >>    /**
> > > >>     * Insert the method's description here.
> > > >>     * Creation date: (24.12.2000 00:33:40)
> > > >>     */
> > > >>    public OdmgExamples(String name)
> > > >>    {
> > > >>        super(name);
> > > >>    }
> > > >>
> > > >>    /**
> > > >>     * Insert the method's description here.
> > > >>     * Creation date: (06.12.2000 21:58:53)
> > > >>     */
> > > >>    public void setUp()
> > > >>    {
> > > >>        databaseName =
> > > >>
> > > >
> > PersistenceBrokerFactory.getConfiguration().getRepositoryFilename();
> > > >
> > > >>
> > > >>    }
> > > >>
> > > >>    /**
> > > >>     * Insert the method's description here.
> > > >>     * Creation date: (06.12.2000 21:59:14)
> > > >>     */
> > > >>    public void tearDown()
> > > >>    {
> > > >>        databaseName = null;
> > > >>    }
> > > >>
> > > >>    /**TestThreadsNLocks state transition of modification states*/
> > > >>    public void testModificationStates()
> > > >>    {
> > > >>        // get facade instance
> > > >>        Implementation odmg = OJB.getInstance();
> > > >>        Database db = odmg.newDatabase();
> > > >>        //open database
> > > >>        try
> > > >>        {
> > > >>            db.open(databaseName, Database.OPEN_READ_WRITE);
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>        ModificationState oldState = StateNewClean.getInstance();
> > > >>        ModificationState newState = oldState.markDirty();
> > > >>        assertEquals(StateNewDirty.getInstance(), newState);
> > > >>
> > > >>        oldState = newState;
> > > >>        newState = oldState.markDirty();
> > > >>        assertEquals(oldState, newState);
> > > >>
> > > >>
> > > >>        // close database
> > > >>        try
> > > >>        {
> > > >>            db.close();
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>
> > > >>    }
> > > >>
> > > >>    public void testOdmgSession()
> > > >>    {
> > > >>        // get facade instance
> > > >>        Implementation odmg = OJB.getInstance();
> > > >>        Database db = odmg.newDatabase();
> > > >>        //open database
> > > >>        try
> > > >>        {
> > > >>            db.open(databaseName, Database.OPEN_READ_WRITE);
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>        Transaction tx = odmg.newTransaction();
> > > >>
> > > >>        //perform transaction
> > > >>        try
> > > >>        {
> > > >>            tx.begin();
> > > >>
> > > >>            Article example = new Article();
> > > >>            example.setArticleId(777);
> > > >>            db.makePersistent(example);
> > > >>
> > > >>
> > > >>
> > > >>            // modify Object
> > > >>            example.setStock(333);
> > > >>            example.addToStock(47);
> > > >>            example.addToStock(7);
> > > >>            example.addToStock(4);
> > > >>
> > > >>
> > > >>            //System.out.println("now commit all changes...");
> > > >>            tx.commit();
> > > >>        }
> > > >>        catch (Exception ex)
> > > >>        {
> > > >>            tx.abort();
> > > >>        }
> > > >>
> > > >>        // close database
> > > >>        try
> > > >>        {
> > > >>            db.close();
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>    }
> > > >>
> > > >>    public void testOQLQuery()
> > > >>    {
> > > >>        // get facade instance
> > > >>        Implementation odmg = OJB.getInstance();
> > > >>        Database db = odmg.newDatabase();
> > > >>        //open database
> > > >>        try
> > > >>        {
> > > >>            db.open(databaseName, Database.OPEN_READ_WRITE);
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>        Transaction tx = odmg.newTransaction();
> > > >>
> > > >>        //perform transaction
> > > >>        try
> > > >>        {
> > > >>            tx.begin();
> > > >>
> > > >>
> > > >>            OQLQuery query = odmg.newOQLQuery();
> > > >>            query.create("select anArticle from " +
> > > >>
> > > > Article.class.getName() + " where articleId = 7");
> > > >
> > > >>            List results = (List) query.execute();
> > > >>
> > > >>            Article a = (Article) results.get(0);
> > > >>
> > > >>
> > > >>            // cross check with PersistenceBroker lookup
> > > >>            // 1. get OID
> > > >>            Article example = new Article();
> > > >>            example.setArticleId(7);
> > > >>            Identity oid = new Identity(example);
> > > >>            // 2. lookup object by OID
> > > >>            PersistenceBroker broker =
> > OJB.getInstance().getBroker();
> > > >>            broker.clearCache();
> > > >>            Article b = (Article) broker.getObjectByIdentity(oid);
> > > >>
> > > >>            assertEquals("should be same object", a, b);
> > > >>
> > > >>            //System.out.println("now commit all changes...");
> > > >>            tx.commit();
> > > >>        }
> > > >>        catch (Exception ex)
> > > >>        {
> > > >>            tx.abort();
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>
> > > >>        // close database
> > > >>        try
> > > >>        {
> > > >>            db.close();
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>    }
> > > >>
> > > >>    public void testNrmAndDlists()
> > > >>    {
> > > >>        // get facade instance
> > > >>        Implementation odmg = OJB.getInstance();
> > > >>        Database db = odmg.newDatabase();
> > > >>        //open database
> > > >>        try
> > > >>        {
> > > >>            db.open(databaseName, Database.OPEN_READ_WRITE);
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>        Transaction tx = odmg.newTransaction();
> > > >>
> > > >>        //perform transaction
> > > >>        try
> > > >>        {
> > > >>            tx.begin();
> > > >>
> > > >>
> > > >>            OQLQuery query = odmg.newOQLQuery();
> > > >>            query.create("select x from " +
> > Article.class.getName() + "
> > > >>
> > > > where productGroupId = 7");
> > > >
> > > >>            DList results = (DList) query.execute();
> > > >>
> > > >>
> > > >>            int originalSize = results.size();
> > > >>
> > > >>            OJB.getLogger().info(results);
> > > >>
> > > >>            String name = "gimme fruits !";
> > > >>
> > > >>            db.bind(results, name);
> > > >>            tx.commit();
> > > >>
> > > >>            // clear the cache to make sure things are
> > loaded from RDBMS
> > !
> > > >>            OJB.getInstance().getBroker().clearCache();
> > > >>
> > > >>            tx = odmg.newTransaction();
> > > >>            tx.begin();
> > > >>
> > > >>            // look it up again
> > > >>            DList newResults = (DList) db.lookup(name);
> > > >>
> > > >>            assertEquals(originalSize,newResults.size());
> > > >>            OJB.getLogger().info(results);
> > > >>
> > > >>            tx.commit();
> > > >>
> > > >>
> > > >>        }
> > > >>        catch (Throwable t)
> > > >>        {
> > > >>            tx.abort();
> > > >>            fail("ODMGException: " + t.getMessage());
> > > >>        }
> > > >>
> > > >>        // close database
> > > >>        try
> > > >>        {
> > > >>            db.close();
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>    }
> > > >>
> > > >>
> > > >>
> > > >>    public void testOQLQueryBind()
> > > >>    {
> > > >>        // get facade instance
> > > >>        Implementation odmg = OJB.getInstance();
> > > >>        Database db = odmg.newDatabase();
> > > >>        //open database
> > > >>        try
> > > >>        {
> > > >>            db.open(databaseName, Database.OPEN_READ_WRITE);
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>        Transaction tx = odmg.newTransaction();
> > > >>
> > > >>        //perform transaction
> > > >>        try
> > > >>        {
> > > >>            tx.begin();
> > > >>
> > > >>
> > > >>            OQLQuery query = odmg.newOQLQuery();
> > > >>            query.create("select anArticle from " +
> > > >>
> > > > Article.class.getName() + " where articleId = $678");
> > > >
> > > >>            query.bind(new Integer(7));
> > > >>
> > > >>            List results = (List) query.execute();
> > > >>
> > > >>            Article a = (Article) results.get(0);
> > > >>
> > > >>            //crosscheck with PersistenceBroker lookup
> > > >>            // 1. get OID
> > > >>            Article example = new Article();
> > > >>            example.setArticleId(7);
> > > >>            Identity oid = new Identity(example);
> > > >>
> > > >>            ObjectCacheFactory.getObjectCache().clear();
> > > >>            // 2. lookup object by OID
> > > >>            PersistenceBroker broker =
> > OJB.getInstance().getBroker();
> > > >>            broker.clearCache();
> > > >>            Article b = (Article) broker.getObjectByIdentity(oid);
> > > >>
> > > >>            assertEquals("should be same object", a, b);
> > > >>
> > > >>            //System.out.println("now commit all changes...");
> > > >>            tx.commit();
> > > >>        }
> > > >>        catch (Exception ex)
> > > >>        {
> > > >>            tx.abort();
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>
> > > >>        // close database
> > > >>        try
> > > >>        {
> > > >>            db.close();
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>    }
> > > >>
> > > >>    public void tesOQLQueryOnCollections()
> > > >>    {
> > > >>        // get facade instance
> > > >>        Implementation odmg = OJB.getInstance();
> > > >>        Database db = odmg.newDatabase();
> > > >>        //open database
> > > >>        try
> > > >>        {
> > > >>            db.open(databaseName, Database.OPEN_READ_WRITE);
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>        Transaction tx = odmg.newTransaction();
> > > >>
> > > >>        //perform transaction
> > > >>        try
> > > >>        {
> > > >>            tx.begin();
> > > >>            OQLQuery query = odmg.newOQLQuery();
> > > >>            query.create("select aLotOfArticles from " +
> > > >>
> > > > Article.class.getName() + " where productGroupId = 4");
> > > >
> > > >>            DCollection results = (DCollection) query.execute();
> > > >>            results = results.query("price > 35");
> > > >>
> > > >>            // now perform control query
> > > >>            query = odmg.newOQLQuery();
> > > >>            query.create("select aLotOfArticles from " +
> > > >>
> > > > Article.class.getName() + " where productGroupId = 4 and
> > price  > 35");
> > > >
> > > >>            DCollection check = (DCollection) query.execute();
> > > >>
> > > >>            assertEquals(results, check);
> > > >>
> > > >>
> > > >>            tx.commit();
> > > >>        }
> > > >>        catch (Exception ex)
> > > >>        {
> > > >>            tx.abort();
> > > >>            ex.printStackTrace();
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>
> > > >>        // close database
> > > >>        try
> > > >>        {
> > > >>            db.close();
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            fail("ODMGException: " + ex.getMessage());
> > > >>        }
> > > >>    }
> > > >>
> > > >>
> > > >>    /**try to open non-existing db*/
> > > >>    public void tesWrongDbName()
> > > >>    {
> > > >>        // get facade instance
> > > >>        OJB objectserver = OJB.getInstance();
> > > >>        Database db = objectserver.newDatabase();
> > > >>
> > > >>        //try open database with non existing repository file:
> > > >>        String wrongDatabaseName = "ThereIsNoSuchFile";
> > > >>        try
> > > >>        {
> > > >>            db.open(wrongDatabaseName, Database.OPEN_READ_WRITE);
> > > >>            fail("should not be able to open database " +
> > > >>
> > > > wrongDatabaseName);
> > > >
> > > >>        }
> > > >>        catch (ODMGException ex)
> > > >>        {
> > > >>            return;
> > > >>        }
> > > >>    }
> > > >>}
> > > >>
> > > >>
> > > >
> > > >
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