Question

Null @Embedded objects in Java Persistence

Asked by: todd_farmer

I have entity objects that I am using with Java Persistence.  These objects (for example, Person) use @Embedded annotations on things like addresses, so properties look like:

@Entity
@Table(name="person")
public class Person implements Serializable {

@Id
@GeneratedValue
private Long id;
private String firstName;
private String lastName;
@Embedded
private Address homeAddress;

...

The problem that I'm having is that I can't control when the Address object is null.  The code above is simplified - I can understand having a null Address object when there are no properties of the Address object.  My domain objects are a little more complex, and there are times where all properties of the embedded object are, in fact, null.  But I don't want the object itself to be null.  I tried explicitly setting the object to a new instance before persisting it:

Person p = new Person();
p.setFirstName("Todd");
p.setHomeAddress(new Address());

// persist it here

But when I retrive that Person from the database, I get back a Person that has a null Address:

p.getHomeAddress().getCity();  // null pointer exception here!

I have searched the API, and found no way to control this behavior.  Has anybody run into this and found a solution, or do I need to explicitly test for null embedded objects when I use retrieve the objects from the database?

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Asked On
2006-08-06 at 09:16:20ID21944922
Tags

java

,

persistence

,

embedded

,

object

Topic

Java Programming Language

Participating Experts
2
Points
500
Comments
11

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Answers

 

by: CEHJPosted on 2006-08-06 at 10:05:09ID: 17259353

>>p.setHomeAddress(new Address());

>>p.getHomeAddress().getCity();  // null pointer exception here!

How can it have a city when one (per the above) has not been set?

 

by: todd_farmerPosted on 2006-08-06 at 10:34:29ID: 17259448

It can't - city should be null.  The problem is that I get a null pointer exception because p.getHomeAddress() is null.  Again, remember that this is a simplified domain model, and only exists to demonstrate the issue.  As best I can tell, if any of the properties of the embedded object are not null, the embedded object itself is not null.  But if all of the properties of the embedded object are null, the embedded object is null when retrieved from the database.

I figure I can work around this by making sure that one property is always not null, but that's not a real solution.

 

by: CEHJPosted on 2006-08-06 at 15:14:08ID: 17260241

you can avoid the NPE by

Address a = p.getHomeAddress();
String city = null;
if(a != null) {
    city = a.getCity();
}

 

by: todd_farmerPosted on 2006-08-06 at 16:00:36ID: 17260465

I'm implementing a workaround similar, but I'm looking to find out whether this is configurable behavior in the Java Persistence API.  I've scanned the specification for JSR-220 related to persistence, but cannot find anything defining expected (or required) behavior.

 

by: objectsPosted on 2006-08-06 at 16:00:50ID: 17260467

If your bean does not have an address then it *should* be null.
use something like commons beanutils to get bean properties

 

by: objectsPosted on 2006-08-06 at 16:12:04ID: 17260496

and are you sure your properties correctly map to your fiesl names, and you have annoted Address correctly?

 

by: todd_farmerPosted on 2006-08-06 at 16:20:19ID: 17260515

Yeah - everything maps correctly.  When I persist a Person that has an Address with non-null properties (p.getAddress().setCity("Los Angeles");), everything works fine.  But when the Address object is not null - but the properties of the Address object are all null - I get a null back for the Address object when retrieving it from the database.  Perhaps this is expected behavior - but I can't find it documented anywhere.  If all the properties of the embedded object are null, the embedded object itself becomes null when retrieved from the database.

 

by: CEHJPosted on 2006-08-06 at 23:50:24ID: 17261715

I'm not sure why you'd want a non-null Address if it has no properties, so the above workaround should be OK

 

by: objectsPosted on 2006-08-07 at 01:24:25ID: 17261983

> so the above workaround should be OK

its unnecessary for a start

20120131-EE-VQP-002

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