Question

Take a look at the first example of http://code.google.com/intl/sv-SE/appengine/docs/java/datastore/jdo/relationships.html (Owned One-to-One Relationships).

I dont quite understand one thing.
If i get a Employee from my PersistanceManager, will i get the ContactInfo at the same time, or will it get the ContactInfo when i try to use it?

If it does get it at the same time, how about Owned One-to-Many Relationsships?
Just to make an example,lets say Employee has a List containing 100 ContactInfos.
Does this mean i will get all the 100 ContactInfos when i get my Employee?

Thanks
//F

Answer 1

By default you will not get child data when you load the parent data. However, if you try and access the child it will be loaded at that time. This is called lazy loading. An important note is that once you have closed the JDO transaction if you try and access a lazily loaded property you will get an exception (since the entity is now detached).

You can configure eager loading on an entity using JDO fetch groups. Eager loading will load all the child data when you load the parent. This is useful if you need to access the property after a transaction or if you need to send the entity across the network to a client.

Recommended reading:

Fetch Groups

JDO Layer Design