How to model parent child relationship with DPL? @Transient?

Question

Hello All,
I want to model a parent entity object with a collection of child entities:
@Entity
public class Parent{
@PrimaryKey
String uuid;
List<Child> children;
@Entity
public class Child{
@PrimaryKey
String id;
I know that the DPL won't support automatic persistence where it'll recursively go through my parent bean and persist my children with one call. Is there a way of applying the equivalent to JPA's @Transient annotation on "children" so I can persist the children manually and have the engine ignore the collection?
If not and I want to return to the user a Parent with a List named "children," do I have to create a new object which is identical to Parent, but doesn't have the BDB annotations and manually assemble everything? If possible, I'd like to avoid defining redundant objects.
Thanks in advance,
Steven
Harvard Children's Hospital Informatics Program
Edited by: JavaGeek_Boston on Oct 29, 2008 2:22 PM

Answer 1

Hi Steven,
The definition of persistence is here:
http://www.oracle.com/technology/documentation/berkeley-db/je/java/com/sleepycat/persist/model/Entity.html
And includes this: "All non-transient instance fields of an entity class, as well as its superclasses and subclasses, are persistent. static and transient fields are not persistent."
So you can use the Java transient keyword. If that isn't practical because you're using transient in a different way for Java serialization, see the JE @NotPersistent annotation.
In general a parent-child relationship between entities is implemented almost as you've described, but with a parentId secondary key in the Child to index all children by their parent. This enables a fast lookup of children by their parent ID.
I suggest looking at this javadoc:
http://www.oracle.com/technology/documentation/berkeley-db/je/java/com/sleepycat/persist/SecondaryIndex.html
as it describes all types of entity relationships and the trade-offs involved. The department-employee relationship in these examples is a parent-child relationship.
--mark