Hibernate mapping doubt

[Valmir Cinquini]

Hi everybody. I'm new on Java world and Hiernate. Since I'm working on a project that must be delivered soon, I haven't got too much time for reading books or documentation about Hibernate. I believe my question is simple.

1) Tables: Sql Server 2005

    CREATE TABLE [dbo].[father](  
        [father_id] [int] IDENTITY(1,1) NOT NULL,  
        [father_descr] [varchar](20) NULL,  
    CONSTRAINT [PK_father] PRIMARY KEY CLUSTERED   
    (  
        [father_id] ASC  
    ) ON [PRIMARY]  
      
    GO  
     
   CREATE TABLE [dbo].[child](  
       [child_id] [int] IDENTITY(1,1) NOT NULL,  
       [father_Id] [int] NOT NULL,  
       [child_descr] [varchar](20) NULL,  
   CONSTRAINT [PK_child] PRIMARY KEY CLUSTERED   
   (  
       [child_id] ASC  
   ) ON [PRIMARY]  
     
   GO  
     
  ALTER TABLE [dbo].[child]  WITH CHECK ADD  CONSTRAINT [FK_child_father] FOREIGN KEY([father_Id]) REFERENCES [dbo].[father] ([father_id])  
  GO  
  ALTER TABLE [dbo].[child] CHECK CONSTRAINT [FK_child_father]  
  GO  

Hibernate hbm mapping files (Havent seen how to do that using Annotations)

  <hibernate-mapping>  
       <class name="father" table="father">  
           <meta attribute="class-description">  
               Table father  
           </meta>  
           <id name="fatherId" type="java.lang.Integer" column="father_id">  
               <generator class="native"/>  
           </id>  
           <property name="descr" type="java.lang.String" column="father_descr"  length="20" />  
                  <set name="childs" table="childs" cascade="all" inverse="true">  
               <key column="father_ID" />  
               <many-to-many column="child_ID" class="child" />  
           </set>      
       </class>  
   </hibernate-mapping>  

and

 <hibernate-mapping>  
     <class name="child" table="child">  
           <meta attribute="class-description">  
               Table child  
           </meta>  
           <id name="childId" type="java.lang.Integer" column="child_id">  
               <generator class="native"/>  
           </id>  
           <property name="descr" type="java.lang.String" column="child_descr"  length="20" />  
     </class>  
   </hibernate-mapping>  

The code:

    public class Teste {  
      
        public static void main(String[] args) {  
            Teste t = new Teste();  
            t.saveFamilia();  
        }  
          
        public void saveFamilia()  {  
               Session session = HibernateUtil.getSessionFactory().openSession();  
               Transaction transaction = null;  
               Integer fatherId = null;  
                 
               try {  
                   transaction = session.beginTransaction();  
                   father father = new father();  
                   father.setDescr("Valmir");  
                   child child = new child();  
                   child.setDescr("Isadora");  
                   father.getchilds().add(child);  
                   fatherId = (Integer) session.save(father);  
                   transaction.commit();  
               } catch (HibernateException e) {  
                   transaction.rollback();  
                   e.printStackTrace();  
               } finally {  
                   session.close();  
               }  
       }  
   }  

When I execute, I got this error:

Hibernate: insert into father (father_descr) values (?)
Hibernate: insert into child (father_Id, child_descr) values (?, ?)
4875 [main] WARN org.hibernate.util.JDBCExceptionReporter - SQL Error: 515, SQLState: 23000
4875 [main] ERROR org.hibernate.util.JDBCExceptionReporter - Cannot insert the value NULL into column 'father_Id', table 'TesteHibernate.dbo.child'; column does not allow nulls. INSERT fails.
org.hibernate.exception.ConstraintViolationException: could not insert: [child]


I always thougt that Hibernate should know that when saving the father, it should use the father id (generated by sql server) as a value for the column child_id automaticaly, i mean by itself.

Why I must save the Father, set child_id in class child with the father_id and after call update (as above)?

    transaction = session.beginTransaction();  
   father father = new father();  
    father.setDescr("Valmir");  
    fatherId = (Integer) session.save(father);  
    child child = new child();  
    child.setDescr("Isadora");  
    [b]child.setfatherId(fatherId);[/b]  
    father.getchilds().add(child);  
    session.update(father);  
   transaction.commit();   

Thanks in advance, and excuse me my poor English