Question

I want to avoid serialisation ( in JMS / AMF ) but still persist the field with JPA/Hibernate.

Is the transient modifier my friend ? Are @Transient annotation and the transient modifier related or not a all ?

The java specification precise that a transient field will not be saved to a persistent storage by a system service. But is hibernate a system service ? ( i dont think so )
http://java.sun.com/docs/books/jls/second_edition/html/classes.doc.html#78119

And java.io.Serialisable seams to indicate that a out.writeObject and in.readObject are called for serialisation
http://download.oracle.com/javase/1.4.2/docs/api/java/io/Serializable.html

Any insight ?

Maybe should i just write a quick test, but i will be more confident with a piece of spec.

Thank !

Answer 1

Is the transient modifier my friend ? Are @Transient annotation and the transient modifier related or not a all ?

They are not really related but I’m afraid they won’t be your friend anyway, transient properties aren’t persisted by Hibernate/JPA. The JPA specification puts it like this:

2.1.1 Persistent Fields and Properties

The persistent state of an entity is
accessed by the persistence provider
runtime either via JavaBeans style
property accessors or via instance
variables. A single access type (field
or property access) applies to an
entity hierarchy. When annotations are
used, the placement of the mapping
annotations on either the persistent
fields or persistent properties of the
entity class specifies the access type
as being either field – or property –
based access respectively.

• If the entity has field-based access, the persistence provider
  runtime accesses instance variables
  directly. All non-transient
  instance variables that are not
  annotated with the Transient
  annotation are persistent. When
  field-based access is used, the
  object/relational mapping annotations
  for the entity class annotate the
  instance variables.
• If the entity has property-based access, the persistence provider
  runtime accesses persistent state via
  the property accessor methods. All
  properties not annotated with the
  Transient annotation are persistent.
  The property accessor methods must be
  public or protected. When
  property-based access is used, the
  object/relational mapping annotations
  for the entity class annotate the
  getter property accessors.
• Mapping annotations cannot be applied to fields or properties that
  are transient or Transient.
• The behavior is unspecified if mapping annotations are applied to
  both persistent fields and properties
  or if the XML descriptor specifies use
  of different access types within a
  class hierarchy.

…

References

• JPA 1.0 specification
  • Section 2.1.1 Persistent Fields
• Hibernate Core Reference Guide
  • 2.2.2. Mapping simple properties

Related questions

• Why does JPA have a @Transient annotation?