JPA with MySQL-Data-Source

Question

Hello Forum,
I have a question regarding usage of a MySQL-Data-Source in combination with JPA
on the SAP NetWeaver Application Server, Java ™ EE 5 Edition.
I have setup a custom datasource like explained in paper:
"Working with Database Tables, DataSources and JMS Resources"
- registered the database driver via telnet (Using mysql-connector-java-5.0.3-bin.jar)
- created the data-sources.xml file underneath the META-INF dir of the EAR project
[code]
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE data-sources SYSTEM "data-sources.dtd" >
<data-sources>
  <data-source>
    <data-source-name>titan_cruises_ds</data-source-name>
    <driver-name>mysql-connector-java-5.0.3-bin.jar</driver-name>
     <init-connections>1</init-connections>
     <max-connections>10</max-connections>
     <max-time-to-wait-connection>60</max-time-to-wait-connection>
     <expiration-control>
          <connection-lifetime>600</connection-lifetime>
          <run-cleanup-thread>60</run-cleanup-thread>
     </expiration-control>
     <sql-engine>native_sql</sql-engine>
    <jdbc-1.x>
      <driver-class-name>com.mysql.jdbc.Driver</driver-class-name>
      <url>jdbc:mysql://ourHost.internal.com:3306/practise_titan_cruises</url>
      <user-name>myUser</user-name>
      <password>myPass</password>
    </jdbc-1.x>
  </data-source>
</data-sources>
[/code]
After that I manually created the persistence.xml underneath the META-INF dir of the EJB project.
[code]
<persistence xmlns="http://java.sun.com/xml/ns/persistence" version="1.0">
     <persistence-unit name="titan_cruises_pu">
          <jta-data-source>titan_cruises_ds</jta-data-source>
     </persistence-unit>
</persistence>
[/code]
After that I created the Entity named "Cabin" and the corresponding table within the db.
Entity code:
[code]
package de.collogia.beans.pojo.ship;
import java.io.IOException;
import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
This persisted POJO class models the cabin data.
<p>
In this class persistence annotations are placed on the getter methods
of the attributes. This tells the persistence manager to access them
via the corresponding get- and set-Methods.</p>
(Unfortunately this does not work on NetWeaver and I had to place them
on field level aggain...)
@author Henning Malzahn ([email protected])
svn-revision:         $Rev:: 670                                           $:
svn-lasted-edited-by: $Author:: henning                                    $:
svn-last-changed:     $Date:: 2007-02-21 21:49:51 +0100 (Wed, 21 Feb 2007) $:
@Entity
@Table(name = "cabin")
public class Cabin implements Serializable {
    /** The generated serial version UID used for serialization. */
    private static final long serialVersionUID = -8522497314498903378L;
    /** The actual version number of this class used for serialization. */
    private static int actualVersion = 1;
    /** The cabin's id. */
    @Id
    @GeneratedValue
    @Column(name = "id")
    private long id;
    /** The cabin's name */
    @Column(name = "name")
    private String name;
    /** The cabin's deck level */
    @Column(name = "deck_level")
    private int deckLevel;
    /** The cabin's ship id */
    @Column(name = "ship_id")
    private int shipId;
    /** The cabin's bed count */
    @Column(name="bed_count")
    private int bedCount;
/---- Serialization/ Deserialization methods -/
Method that is responsible for deserialization of the object.
@param in The <code>ObjectInputStream</code> object to read
          the data from.
@throws IOException That may occur when reading from the
                    <code>ObjectInputStream</code> object
@throws ClassNotFoundException That may occur when invoking the default
                               deserialization mechanism.
    private void readObject(final java.io.ObjectInputStream in)
        throws IOException, ClassNotFoundException {
        /* Invoke default deserialization mechanism. */
        in.defaultReadObject();
        /* Read the actual version number of the class. */
        actualVersion =  in.readInt();
    } // End of readObject()
Method that is responsible for serialization of the object.
@param out The <code>ObjectOutputStream</code> object to write
           the data to.
@throws IOException That may occur when writing to the
                    <code>ObjectOutputStream</code> object.
    private void writeObject(final java.io.ObjectOutputStream out)
        throws IOException {
        /* Invoke default serialization mechanism. */
        out.defaultWriteObject();
        /* Write the actual version number of the class. */
        out.writeInt(actualVersion);
    } // End of writeObject()
/---- Defining constructors -/
Private default constructor.
    private Cabin() {
    } // End of default constructor
Full constructor.
@param name The cabin's name.
@param deckLevel The cabin's deck level.
@param shipId The cabin's ship id.
@param bedCount The cabin's bed count.
    public Cabin(final String name,
                 final int deckLevel,
                 final int shipId,
                 final int bedCount) {
        this.name = name;
        this.deckLevel = deckLevel;
        this.shipId = shipId;
        this.bedCount = bedCount;
    } // End of full constructor
/---- Overridden class methods -/
Returns a string representation of the cabin's data.
@see java.lang.Object#toString()
    @Override
    public String toString() {
        StringBuffer strBuf = new StringBuffer();
        strBuf.append(this.name);
        strBuf.append("\n");
        strBuf.append(this.deckLevel);
        strBuf.append("\n");
        strBuf.append(this.shipId);
        strBuf.append("\n");
        strBuf.append(this.bedCount);
        return strBuf.toString();
    } // End of toString()
/---- Defining instance methods -/
Get method for the member "<code>id</code>".
@return Returns the id.
    public long getId() {
        return this.id;
Set method for the member "<code>id</code>".
HTDODO hm: Check whether it is possible to have setId method
using private accesss level with NetWeaver JPA-Provider!
@param id The id to set.
    private void setId(final long id) {
        this.id = id;
Get method for the member "<code>name</code>".
@return Returns the name.
    public String getName() {
        return this.name;
Set method for the member "<code>name</code>".
@param name The name to set.
    public void setName(final String name) {
        this.name = name;
Get method for the member "<code>deckLevel</code>".
@return Returns the deckLevel.
    public int getDeckLevel() {
        return this.deckLevel;
Set method for the member "<code>deckLevel</code>".
@param deckLevel The deckLevel to set.
    public void setDeckLevel(final int deckLevel) {
        this.deckLevel = deckLevel;
Get method for the member "<code>shipId</code>".
@return Returns the shipId.
    public int getShipId() {
        return this.shipId;
Set method for the member "<code>shipId</code>".
@param shipId The shipId to set.
    public void setShipId(final int shipId) {
        this.shipId = shipId;
Get method for the member "<code>bedCount</code>".
@return Returns the bedCount.
    public int getBedCount() {
        return this.bedCount;
Set method for the member "<code>bedCount</code>".
@param bedCount The bedCount to set.
    public void setBedCount(final int bedCount) {
        this.bedCount = bedCount;
} // End of class Cabin
[/code]
After that I created the TravelAgentBean, a Stateless Session Bean, implementing
a remote interface that allows construction and persisting of new Cabin objects:
[code]
package de.collogia.beans.session.stateless;
import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import de.collogia.beans.pojo.ship.Cabin;
Class that implements the <code>TravelAgentRemote</code> interface
and defines the business methods of the TravelAgent service.
@author Henning Malzahn ([email protected])
svn-revision:         $Rev:: 670                                           $:
svn-lasted-edited-by: $Author:: henning                                    $:
svn-last-changed:     $Date:: 2007-02-21 21:49:51 +0100 (Wed, 21 Feb 2007) $:
@Stateless
public class TravelAgentBean implements TravelAgentRemote {
    /** The <code>Log</code> object for this class. */
//    private static final Log LOGGER;
    /** The <code>PersistenceManager</code> object. */
    @PersistenceContext(unitName = "titan_cruises_pu")
    EntityManager em;
/---- Static initializer -/
//    static {
//        LOGGER = LogFactory.getLog(TravelAgentBean.class);
//    } // End of static initializer block
/---- Implementing remote interface methods -/
{@inheritDoc}
    public void createCabin(final Cabin cabin) {
        this.em.persist(cabin);
    } // End of createCabin()
} // End of class TravelAgentBean
[/code]
After that I created a Controller class containing a main method that looks up the remote
interface of the TravelAgentBena like explained in document "Accessing Enterprise JavaBeans Using JNDI
in SAP NetWeaver Application Server, Java ™ EE 5 Edition" written by Validimir Pavlov of SAP NetWeaver
development team.
Unfortunately I receive an Exception after invoking the createCabin(...) method.
On the console of the NWDS I receive:
[code]
javax.ejb.EJBException: Exception in getMethodReady() for stateless bean sap.com/test2Earannotation|test2Ejb.jarannotation|TravelAgentBean;
nested exception is: com.sap.engine.services.ejb3.util.pool.PoolException: javax.ejb.EJBException: Cannot perform injection over bean instance
Caused by: java.lang.RuntimeException: The persistence unit is inconsistent:
The entity >>de.collogia.beans.pojo.ship.Cabin<< is mapped to the table >>cabin<<, which does not exist.
[/code]
But if I look at the log file located in "C:\NWAS_JAVAEE5\JP1\JC00\j2ee\cluster\server0\log\defaultTrace.0.trc"
I see the real reason is:
[code]
[EXCEPTION]
#6#1064#42000#You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax
to use near '"cabin"' at line 1#collnx02.collogia.de:3306:null:practise_titan_cruises#select * from "cabin"#com.mysql.jdbc.exceptions.MySQLSyntaxErrorException:
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '"cabin"' at line 1
     at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:936)
     at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2870)
     at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1573)
     at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1665)
     at com.mysql.jdbc.Connection.execSQL(Connection.java:3124)
     at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1149)
     at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1262)
     at com.sap.sql.jdbc.basic.BasicPreparedStatement.executeQuery(BasicPreparedStatement.java:99)
     at com.sap.sql.jdbc.direct.DirectPreparedStatement.executeQuery(DirectPreparedStatement.java:307)
     at com.sap.sql.jdbc.direct.DirectPreparedStatement.executeQuery(DirectPreparedStatement.java:264)
     at com.sap.engine.services.dbpool.wrappers.PreparedStatementWrapper.executeQuery(PreparedStatementWrapper.java:274)
[/code]
My goodness - what a long post - sorry for this - I hope I provided all information
necessary to deal with the issue.
Am I thinking in the right direction to blame attribute [code]<sql-engine>native_sql</sql-engine>[/code]
of file data-sources.xml for the beaviour? Are there any other argument options than native_sql?
Thanks in Advance!
Henning Malzahn

Answer 1

Hi Henning,
> Despite the fact it's working now I have to do some
> changes to my code currently
> developed using JBoss/ Hibernate combination.
> Hibernate allows you to have the
> default no-arg constructor with private visibility -
> any special reason for the fact that
> only protected is allowed on NetWeaver?
Here we strictly implemented the checks according to the requirements of the JPA specification. Technically, we could do with private constructors as well. But the JPA specifications requires the constructor to be protected to allow a JPA implementation to subclass entities if needed.
> The entities in the project are final classes
> so declaring a ctor protected doesn't really make
> sense...
For the same reason, your entities should not be final. Are we missing a check here ?
> Also the persistence.xml parameter
>
hibernate.hbm2ddl.auto
with the value of
> create-drop is very useful while
> developing the app - everytime you deploy the project
> you get a fresh database.
> Is there a comparable option for NetWeaver?
No, unfortunately, there is no comparable option in SAP JPA (yet). We understand that there is a need for forward mapping. We would have liked to delegate this task to the JPA design time (i.e. Dali). However, we had to discover that Dali does not perform this task properly and we can't recommend using it any more.
Consequently, there is no automatic schema generation in SAP JPA 1.0.
>
> Another thing is the extra TMP_SEQUENCE table which
> isn't necessary using JBoss and
> Hibernate - what's the reason for that?
With Hibernate Entity Manager, the id generation strategy in use with GenerationType.AUTO depends on the database dialect. This means that depending on the database dialect, IDENTITY columns, SEQUENCES or generator tables (TableHiLo) are required. As Hibernate has the before mentioned schema generation property this fact can be hidden to the user.
In SAP JPA, we are always using a table generator if GenerationType.AUTO is used. This allows for better portability across databases. It requires the table TMP_SEQUENCE. As we unfortunately do not have a schema generation capability, the user must create this table.
Best regards,
Adrian