Comment rattacher un objet à la session EclipseLink après désérialisation
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02-10-2019 - |
Question
Voici simple POC:
public void main(String[] args) {
final String FILE_NAME = "c:/poc.ser";
try {
HotelJdo hotel = HotelJdoFinder.findById(430);
ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(FILE_NAME));
// serialize the object
oos.writeObject(hotel);
oos.close();
// read the object in the same vm
ObjectInputStream ois = new ObjectInputStream(new FileInputStream(FILE_NAME));
HotelJdo hotel2 = (HotelJdo) ois.readObject();
// this line throws an exception
System.out.println("number of crs channels: " + hotel2.getAvailableRooms().size());
ois.close();
} catch (Exception e) {
System.out.println("Unexpected exception:");
e.printStackTrace();
}
}
hotel2.getAvailableRooms () interroge la liste des pièces qui configuré pour utiliser indirection transparent. Et cet appel lève l'exception suivante:
Exception [EclipseLink-7242] (Eclipse Persistence Services - 1.2.1.v20100428-r70
82): org.eclipse.persistence.exceptions.ValidationException
Exception Description: An attempt was made to traverse a relationship using indi
rection that had a null Session. This often occurs when an entity with an unins
tantiated LAZY relationship is serialized and that lazy relationship is traverse
d after serialization. To avoid this issue, instantiate the LAZY relationship p
rior to serialization.
at org.eclipse.persistence.exceptions.ValidationException.instantiatingV
alueholderWithNullSession(ValidationException.java:975)
at org.eclipse.persistence.internal.indirection.QueryBasedValueHolder.in
stantiate(QueryBasedValueHolder.java:83)
at org.eclipse.persistence.internal.indirection.QueryBasedValueHolder.in
stantiate(QueryBasedValueHolder.java:75)
at org.eclipse.persistence.internal.indirection.DatabaseValueHolder.getV
alue(DatabaseValueHolder.java:83)
at org.eclipse.persistence.indirection.IndirectList.buildDelegate(Indire
ctList.java:237)
at org.eclipse.persistence.indirection.IndirectList.getDelegate(Indirect
List.java:397)
at org.eclipse.persistence.indirection.IndirectList.size(IndirectList.ja
va:726)
Je comprends que je peux l'initialisation de déclenchement de la liste des chambres avant sérialisation mais je me demande comment puis-je rattacher à l'objet hotel2 session de EclipseLink afin d'obtenir la liste des chambres paresseusement.
La solution
Pour refixer un objet, vous devez utiliser la méthode EntityManager.merge
avant d'accéder à ses relations.
Quelque chose comme:
hotel2 = em.merge(hotel2);
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