App engine does not store List when it is annotated with serializable and defaultFetchGroup set

I am trying to store an Jdo which has a 开发者_Python百科List in it. When the list is annotated with

@Persistent (defaultFetchGroup = "true")

It works fine, but when I have

@Persistent (serializable = "true", defaultFetchGroup = "true")

It does not store the list. Does anyone know why? What do I do when I have a list of custom objects that I want to store, do I mark them as serializable or not?

I see 3 cases :

1. a core type (List<String>,List<Date>, etc...) : You should use @Persistent
2. a @PersistenceCapable class (List<MyPersistenceCapableClass>) : You should use @Persistent, it's the One-To-Many relationship case
3. not a core type neither a @PersistenceCapable class but a @Serializable one (List<MySerializableClass>) : You must use @Persistent (serializable = "true")

When using serializable = "true", you need to call JDOHelper.makeDirty to notify JDO everytime you modify the list :

MySerializableClass serializableObject = new MySerializableClass();
persistedObject.getMySerializableClassList().add(serializableObject);
JDOHelper.makeDirty(persistedObject, "mySerializableClassList");

note : the defaultFetchGroup = "true" parameter is used to tell JDO to automatically fetch all objects of the list, and not wait for access to the field (lazy fetching).

@Persistent(serialized = "true", defaultFetchGroup="true") is the correct annotation.

Also when you are changing something to an element of the list you should call JDOHelper.makeDirty(this, "yourSerializedField"); because when it re-serialize the element it only looks at the reference not at each item (it uses .equals of the object) Hope this helps