Entity Beans extending a POJO - will I ever get this to work

[peterrusselluk]

Since EJBs are now POJOs I would have expected that I could define an Entity Bean that extended a base class with standard methods.

I have been unable to achieve this and get a nnumber of exceptions regarding overiding ID properties among others.

Is this something that should work, or am I never going to get it to work?

thanks in advance

Pete

[ejb3workshop]

Could you be a bit more specific what you are trying to override and what exceptions you are getting. I have implemented inheritance from POJO's, but I also had problems inheriting annotations. Basic services worked fine.

[peterrusselluk]

Here is the Base Class

public class BaseDeptDTOImpl implements Serializable {

 private static final Log log = LogFactory.getLog(BaseDeptDTO.class);


 /** Primary key. */
 private int deptId;

 /**
 * auto_increment
 *
 * Get the primary key.
 *
 * @return The primary key.
 */
 @javax.persistence.Id @javax.persistence.GeneratedValue(strategy=javax.persistence.GenerationType.AUTO)
 @javax.persistence.Column(name = "dept_id")
 public int getDeptId() {
 return deptId;
 }

 /**
 * auto_increment
 *
 * Set the primary key.
 *
 * @param deptId The primary key.
 */
 public void setDeptId(int deptId) {
 this.deptId = deptId;
 }

 /** Regular field. */
 private java.lang.String deptName;

 /**
 * Get the deptName.
 *
 * @return The deptName.
 */
 @javax.persistence.Column(name = "dept_name")
 public java.lang.String getDeptName() {
 return deptName;
 }

 /**
 * Set the deptName.
 *
 * @param deptName The deptName.
 */
 public void setDeptName(java.lang.String deptName) {
 this.deptName = deptName;
 }

 /** Association. */
 private java.util.Collection<tv.probability.referenceimplementation.dto.EmpDTO> emps;
 /**
 * Get the emps.
 *
 * @return The emps.
 */
 @javax.persistence.OneToMany(cascade = javax.persistence.CascadeType.ALL, fetch = javax.persistence.FetchType.EAGER)
 @javax.persistence.JoinColumn(name = "dept_id")
 public java.util.Collection<tv.probability.referenceimplementation.dto.EmpDTO> getEmps() {
 return emps;
 }
 /**
 * Set the emps.
 *
 * @param emps The emps.
 */
 public void setEmps(java.util.Collection<tv.probability.referenceimplementation.dto.EmpDTO> emps) {
 this.emps = emps;
 }
}

and here is the extending class

@javax.persistence.Entity
@org.hibernate.annotations.Entity(dynamicInsert = true)
@javax.persistence.Table(name = "dept")
public class DeptDTOImpl extends BaseDeptDTOImpl implements DeptDTO {
 private static final Log log = LogFactory.getLog(DeptDTOImpl.class);

 /** Primary key. */
 private int deptId;

 /**
 * auto_increment
 *
 * Get the primary key.
 *
 * @return The primary key.
 */
 @javax.persistence.Id @javax.persistence.GeneratedValue(strategy=javax.persistence.GenerationType.AUTO)
 @javax.persistence.Column(name = "dept_id")
 public int getDeptId() {
 return deptId;
 }

 /**
 * auto_increment
 *
 * Set the primary key.
 *
 * @param deptId The primary key.
 */
 public void setDeptId(int deptId) {
 this.deptId = deptId;
 }
}

This compiles and runs, but the inherited deptName is not persisted to the database, it is ommited from the SQL entirely.
If I add the entity annotations to the Base class:

@javax.persistence.Entity
@org.hibernate.annotations.Entity(dynamicInsert = true)
@javax.persistence.Table(name = "dept")

I get the exception:

FATAL 05-02 09:00:24,776 (PersistenceXmlLoader.java:parsePersistenceUnit:101) -refImplDB JTA
ERROR 05-02 09:00:28,605 (AbstractController.java:incrementState:350) -Error installing to Start: name=persistence.units:jar=embeddable-ejb.jar,unitName=refImplDB state=Create
org.hibernate.AnnotationException: Unable to define/override @Id(s) on a subclass: tv.probability.referenceimplementation.dto.DeptDTOImpl

btw. I am running this using EMbeddable EJBs and JUnit.

[ejb3workshop]

I don't know if it is a bug, but I was also unable to inherit annotations. In my case I tried to inherit the @Version and @Id annotations.

[alximik]

Please read ejb 3 spec. In PFD (chapter 2.1.9.2) it is explicitly written that any annotations on non-entity superclass are ignored.

You can use @MappedSuperclass annotation to solve the problem.

[chrismalan]

Hi Peter,

I have successfully extended from a base class in several applications. Other problems crop up so I don't have things too easy, but not this one.

You will find the solution here:
http://docs.jboss.org/ejb3/app-server/tutorial/singleinheritance/single.html

Also, the extended class should have no primary key - the pk is only in the base class.

Do use the single table inheritance method, it works well and is amenable to some changes in your inheritance hierarchy later on, should it be needed.

Hope this helps.