How do I override the targetEntity

prestonfm · **Joined:** Wed Jun 17, 2009 5:27 pm **Posts:** 9

I've created a couple of base class master / detail entity beans. Now I want to descend from them. In order to maintain the new master / detail relationship I need to change the targetEntity in the descendant. How is this done?

Froestel · **Posted:** Wed Oct 07, 2009 8:22 pm

Hi prestonfm,

what do you want to do? Could you probably be more precise and possibly provide some code?

CU
Froestel

prestonfm · **Joined:** Wed Jun 17, 2009 5:27 pm **Posts:** 9

I have two separate databases that contain a report and reportItems table. The table structure is the same for both databases.

I have a session bean that needs to write to each database / table. In order to keep the code simple I want the session bean to work with a base entity bean that then goes to the appropriate table.

To accomplish that, I've created a base entity class call Report and another called ReportItem. The Report class contains a OneToMany relation for the ReportItem class.

Code:

@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public class Report implements Serializable {
  ...    

  @OneToMany(fetch=FetchType.EAGER, cascade={CascadeType.ALL},targetEntity=ReportItem.class)
  @JoinColumn(name="Report_ID", nullable=false)
  private Collection<ReportItem> reportItems = new ArrayList<ReportItem>();

... (set all the other properties)

}

From the Report and ReportItem classes I've descended two additional classes.

Report -> Database1Report & Database2Report

ReportItem -> Database1ReportItem & Database2ReportItem

The base class does not contain a @Table because I really don't want it to write to the database so I declare it in the descendant classes accordingly.

Code:

@Entity
@Table(schema= "Database1", name = "reports")
public class Database1Report extends Report implements Serializable {
    public Database1Report() {}
}

The problem is that now I need my Database1Report class to use Database1ReportItem for it's collection. Without being able to override the targetEntity in the descendant class I don't know how to change the collection that was defined in the base entity class.

I'd like to do something like the AssociationOverrride but it doesn't work for targetEntity

Code:

@AssociationOverride( name="report", targetEntity=Database1Report.class)

Froestel · **Posted:** Sat Oct 10, 2009 3:19 am

Hi prestonfm,

ok, that's better now.

I'm afraid, you have to use Java generics to get to the solution. Something like

Code:

public class Report<T extends ReportItem> implements ... {
...
private Collection<T> reportItems = new ArrayList<T>();
...
}

Then, create your subclasses as, i.e.,

Code:

public class Database1Report<Database1ReportItem> implements ... {
...
}

Java type erasure gets your subclass collections to be limited to the corresponding ReportItem sub-class.

CU
Froestel