Saint Johns Development Team

I try to learn JDO and I have some problems already. After I succeeded to configure datanucleus with spring using HSQLDB, I started to play around.

I have a Worker class and a Tool class. A Worker can have more than one tool so we have a 1-n relationship.

There are 2 ways to define a 1-n relationship. One case is with a foreign key and the other is throw a middle join table.

Here the solution with the foreign key (using Annotations):

public class Worker {

 
 @PrimaryKey
 @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
 private Long id;
 
 @Override
 public String toString() {
  return this.getClass().getName() + " [" +
    "id:"+id+", " +
    "tools:"+getTools()+", " +
    "]";
 }

 @Persistent
 private String name;
 
 @Persistent
 @Element(types=gr.open.thohapi.model.Tool.class)
 private Set tools = new HashSet();
.
.
.
}

and here the solution with the join table (using Annotations):

public class Worker {

 
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
 private Long id;
 
 @Override
 public String toString() {
  return this.getClass().getName() + " [" +
    "id:"+id+", " +
    "tools:"+getTools()+", " +
    "]";
 }

 @Persistent
 private String name;
 
 @Persistent
 @Element(types=gr.open.thohapi.model.Tool.class)
 @Join(table="WORKER_TOOLS", column="WORKER_ID")
 private Set tools = new HashSet();
.
.
.
}