Re: [eclipselink-users] [MOXy] setting bi-directional references during

["polly.c.chang" <polly.c.chang@xxxxxxxxx>]

Hi Matt,

Thank you for the quick and informative response!  :)  I am currently using
EL 1.1.2.  It sounds like there's a good reason to upgrade to 1.2.  I do
have a few more questions though:

1.  The example that you described below would work well for 1:many
bi-directional relationships.  But what about many:many bi-directional
relationships?  For example, if class "A" has a collection of B's, and "B"
has a collection of A's, the code to set the back-reference then looks like:

	public void addB(B b) {
			this.getBs().add(b);
			b.getAs().add(this);
		}
	}

EL 1.2 can take care of this too?

2.  Would the workaround that I have described work?  Does EclipseLink need
public getters and setters if I turn on "method access"?  Or would
private/protected methods be ok?

Thanks!
--Polly



Matt MacIvor wrote:
> 
> Hey Polly, 
> 
> We're currently working on better support for handling bi-directional
> relationship mappings in EclipseLink. Currently in EclipseLink 1.2
> (which is available today) for containment relationships, you can
> configure the mapping to automatically set the back-reference when it's
> populating the collection. This functionality isn't currently exposed
> in the MappingWorkbench but is available through the mapping APIs,
> Project XML and in JAXB through a custom annotation. 
> 
> Using the mapping APIs you would do something like: 
> XMLCompositeCollectionMapping childMapping = new
> XMLCompositeCollectionMapping(); 
> childMapping.setXPath("children/child"); 
> childMapping.setReferenceClass(Child.class); 
> //Specify the name of the attribute on the reference class that points
> back to the container object 
> childMapping.setContainerAttributeName("parent"); 
> childMapping.setContainerGetMethodName("getParent"); 
> childMapping.setContainerSetMethodName("setParent"); 
> parentDescriptor.addMapping(childMapping); 
> 
> If you're using Project XML,  this can also be specified in the xml
> version of the project using the <container-attribute> element on
> the composite mapping. 
> 
> In EclipseLink 1.2 this support is only availabe for Containment based
> mappings (XMLCompositeObjectMapping and XMLCompositeCollectionMapping),
> but EclipseLink 2.0 will have expanded support for bi-directional
> relationships to also include reference mappings. 
> 
> Hope this helps, 
> 
> -Matt 
> 
> polly.c.chang wrote:
> 
>   Hi,
> 
> I have a bi-directional relationship between Parent and Child classes like
> this:
> 
> public class Parent {
>     private List<Child> children;
> 
>     public List<Child> getChildren()
>     public void setChildren(List<Child> children)
>     public void addChild(final Child child) {
>         this.getChildren().add(child);
> 	child.setParent(this);
>     }
>     public void removeChild(final Child child) {
>         this.getChildren().remove(child);
> 	child.setParent(null);
>     }
> }
> 
> public class Child {
>     private Parent parent;
> 
>     public void setParent(Parent parent)
>     public Parent getParent()
> }
> 
> When I unmarshal the Parent object, I find that the "children" collection
> contains Child objects that do not have the back-reference to the Parent. 
> This is probably because the Child objects were unmarshalled and set
> directly into the "children" collection.  How do I change the behavior so
> that EclipseLink MOXy calls the addChild() method for each Child object? 
> I
> looked around EclipseLink Workbench and the schema, but I can't find any
> mappings that look suitable.  Does MOXy support adding objects into a
> collection by calling an add() method?  
> 
> If MOXy does not support calling an add() method for unmarshalling
> collections, then the only workaround that I can think of is to turn on
> "method accessing" for each bi-directional collection so that MOXy uses
> the
> getter and setter methods for the list.  Then the setter needs to go
> through
> the collection and fix up the back references to the Parent.  Usually my
> setter is private/protected, so I assume that I'd have to make it public
> too
> for EclipseLink to use it. 
> 
> What do you recommend?
> 
> Thanks!
> --Polly
>   
> 
> 
> 
> 
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> 
> 

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