Question

I am using DB2 database and hibernate framework. There are two tables such as Word and Litter and their relationship is one to many.

1. Schema A:

   Table Word: ID,
   IDLIT -> references to ID of Litter table
   Name
   

2. Schema B:

   Table Litter ID,
   Short_Name,
   Long_Name.
   

Both tables are located in two different schemas but in one database. I have an POJO and XML mapping files to map the tables. Now how can I save the objects into database while handling the many to one relationship(Litter – Word)? Is the any suggestion? If yes please provide me with detailed instructions, thanks in advance!

Updated question

Also I have changed because my mapping xml files different for each POJO class. Here is the code for running:

 Session session = HibernateUtility.getSessionFactory().openSession();
   session.beginTransaction();

   Word word = new Word();
   Word word1 =new Word();

   Litter litter = new Litter();
   litter.setFullname("bla bla");
   word.setLitter(litter);    
   word1.setLitter(litter); //Here I have to handle one to many relationship

   Set Words =new  HashSet();
   Words.add(word);
   Words.add(word1);
   litter.setWords(words);
   session.save(litter);
   session.save(word);
   session.save(word1);
  session.getTransaction().commit();
  session.close();

But this code giving an exception: JDBCExceptionReporter logExceptions
Is the approach which I am using is correct?

Stack trace------------------
INFO: schema update complete
Hibernate: select max(ID) from LITTER
сен 25, 2012 7:33:42 PM org.hibernate.util.JDBCExceptionReporter logExceptions
WARNING: SQL Error: -204, SQLState: 42704
сен 25, 2012 7:33:42 PM org.hibernate.util.JDBCExceptionReporter logExceptions
SEVERE: DB2 SQL Error: SQLCODE=-204, SQLSTATE=42704, SQLERRMC=BIMASH.LITTER, DRIVER=3.64.104
сен 25, 2012 7:33:42 PM org.hibernate.util.JDBCExceptionReporter logExceptions
WARNING: SQL Error: -204, SQLState: 42704
сен 25, 2012 7:33:42 PM org.hibernate.util.JDBCExceptionReporter logExceptions
SEVERE: DB2 SQL Error: SQLCODE=-204, SQLSTATE=42704, SQLERRMC=BIMASH.LITTER, DRIVER=3.64.104
сен 25, 2012 7:33:42 PM org.hibernate.util.JDBCExceptionReporter logExceptions
WARNING: SQL Error: -727, SQLState: 56098
сен 25, 2012 7:33:42 PM org.hibernate.util.JDBCExceptionReporter logExceptions
SEVERE: DB2 SQL Error: SQLCODE=-727, SQLSTATE=56098, SQLERRMC=2;-204;42704;BIMASH.LITTER, DRIVER=3.64.104
Exception in thread "main" org.hibernate.exception.SQLGrammarException: could not fetch initial value for increment generator
    at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:67)
    at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
    at org.hibernate.id.IncrementGenerator.getNext(IncrementGenerator.java:107)
    at org.hibernate.id.IncrementGenerator.generate(IncrementGenerator.java:44)
    at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:99)
    at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:187)
    at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
    at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:172)
    at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:27)
    at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
    at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:535)
    at org.hibernate.impl.SessionImpl.save(SessionImpl.java:523)
    at org.hibernate.impl.SessionImpl.save(SessionImpl.java:519)
    at Main.main(Main.java:73)

Answer 1

You can define the schema a mapped class belongs to with the schema attribute of the <class> element in the mapping file. Notice this will override the setting in the general <hibernate-mapping>‘s schema attribute.

<!-- A is set to be the default schema -->
<hibernate-mapping schema="A">
    <class name="mypackage.Word" table="WORD" >
    ....
    </class>

    <!-- Overriding the schema definition for this class -->
    <class name="mypackage.Litter" table="LITTER" schema="B">
    ....
    </class>
</hibernate-mapping>

The following Hibernate reference chapter might be worth a read: Chapter 5. Basic O/R Mapping, specially the sections about the <hibernate-mapping> and <class> elements.

UPDATE

Seeing the stack trace, it seems that a <generator class="increment"> is being used in the class. If it’s the case (it seems so by the select max(ID) from LITTER query), you’ll also have to specify the schema in the <generator> so that the issued query transforms into select max(ID) from B.LITTER. You can achieve that with a <param> named schema in the <generator>:

<generator class="increment">
    <param name="schema">B</param>
</generator>

For more details see this almost duplicate question: Hibernate: ID generator using increment and Oracle Schema