Hi I have a question about object identities and cascading saves.

As an example assume I have two classes:

Language which has two fields 'code' for example 'en' and 'name' for example 'English'


Person which has a number of fields 2 related to Language, 'defaultLanguage' and
'languages'.

My application constructs a Person class with the associated Language objects. But I am having 2 problems:

1- if I specify that defaultLanguage is not-null then adding the person class fails with:
not-null property references a null or transient value: domain.Person.defaultLanguage
Note, that Person does have a defaultLanguage (ie it is not null).

2- if the default language is also in the languages set, adding fails telling me:
org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [domain.Language#en]

Perhaps I need to change my PersonDAO class to make sure it creates Language objects prior to trying to save a Person,
but I thought that was the use of cascade.

Perhaps I have messed up with identifiers, although I did override the equals, and hashcode methods of Language.

Most likely I have misunderstood something. I am hoping someone in this forum has gone through the same problem and
can offer me some advice.

Thanks,
Hani

When you want to set an existing language, you must load it into the session or get a link to the one exiting in the session.
transient means that your language is not yet saved and an ID is not created.

example:
language = session.get(1);
if (language == null) // it is transient
{
//set all needed fields
session.save(language);
0
person.getLanguages.add(language);
session.save(person);



Something else:
you may consider to use iso_codes instead of a integer primary key.

Regards Sebastian

Please rate, if this helped out.

Thanks for the reply.

From your example it seems like my PersonDAO.add(Person person) method would need to check if defaultLanguage and languages have
been persisted prior to persisting Person. If that is the case than what
does the cascade="save-update" do? I thought the whole point was that
with cascading I could simply save the person object and the corresponding Language objects would be saved if needed.

Not sure what you meant by int identifiers, my Language object has a
String identifier (user assigned) called 'code'.

Hani

regarding 2: make sure you don't add two different instances in the Person class, i.e. one language as defaultLanguage and a different instance of the same language in the set. Otherwise you have (as the error message says) two different objects with the same identifier.

This is partial right:

when you create a new language instance and a new person instance
and
add the language to your person and save the person than both will be saved if the cascase is properly set.
but:
as language has a defined id, you must be sure that you do not have allready have an instance in your session or in the database. The first case leeds to your exception 1, the second to duplicate key.

If you are unsure, you must look up if the language exists. I say this as I expect that you will generate languages in very rare cases.

You can only have one instance with the same primary key in the same session. session save will not look up an instance of your langauge in the session. session.save tries to regenerate a new instance in the session and will fail if one exist. So if the object may exist in the session than you should be sure that you get this instance or you will get your exception 2
session.get(Langauge.class,'en') will get you this instance.

Sebastian