Getting Error while setting generated id in hibernate

I have a Student object which i need to save in database. The id : studentId is defined like in HBM :-

        <id name="studentId" type="long">
            <column name="ST_ID" />
            <generator class="native" />
        </id>

Now, for generating the ID, i have written the code, which i have generally implemented, same as it was present in hibernate Source, as below :-

// fetching the entity persister for the entity
EntityPersister persister = 
    ((SessionImpl)session.).getEntityPersister(entity.getClass().getName(), entity);

// get the model 
PersistentClass model = configuration.getClassMapping(persister.getEntityName());

// cache concurrency
CacheConcurrencyStrategy strategy = persister.getCache();
Class persiterClass = model.getEntityPersisterClass();

SessionFactoryImpl  sessionFactoryImpl = 
            (SessionFactoryImpl) session.getSessionFactory();

if(persiterClass == null) {     
    persister = new SingleTableEntityPersister(model, strategy, sessionFactoryImpl)
}

this.id = persister.getIdentifierGenerator().generate((SessionImpl)session, entity);

persister.setIdentifier(entity, id, EntityMode.POJO);

Now, when i reach the code line persister.setIdentifier(entity, id, EntityMode.POJO);, I get the following exception :-

IllegalArgumentException in class:
com.school.class.Student, setter method of property: studentId
org.hibernate.property.BasicPropertyAccessor$BasicSetter set
SEVERE: expected type: long, actual value: org.hibernate.id.IdentifierGeneratorFactory$2
org.hibernate.PropertyAccessException: IllegalArgum开发者_开发问答entException occurred while calling setter of com.school.class.Student.studentId
    at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPropertyAccessor.java:104)
    at org.hibernate.tuple.entity.AbstractEntityTuplizer.setIdentifier(AbstractEntityTuplizer.java:211)
    at org.hibernate.persister.entity.AbstractEntityPersister.setIdentifier(AbstractEntityPersister.java:3601)
    at com.school.class.Student.<init>(Student.java:140)

Please Help, as i am unable to understand the error, as I have picked the code same from hibernate. If it works, properly over there, then this code should also work here.

Thanks

---

Some generators can't generate the identifier before the actual insert, therefore they return a special marker object from the generate() method. This object indicates that Hibernate should obtain identifier in different way, using PostInsertIdentifierGenerator.getInsertGeneratedIdentifierDelegate() method.

---

In the HBM File, i mentioned the generator as <generator class="native" />, with which it was not working, then i tried with <generator class="increment"/>, I don't know the exact reason, but it worked properly with that.

I feel the proper reason can be that the identifier generator was POST_INSERT_INDICATOR, which i feel means that the id will be generated after the object is being inserted into the database, whereas I was trying to generate the same before insetion, thats the reason it was failing.

I even tried with other id generators also, Refer This , i tried uuid, assigned, increment, sequence, and hilo, they have worked properly, but native & identity, failed with the same problem.

Any updates to this answer are invited, as even i want to know the exact reason for this thing and will like to know, the exact reason.

---

That error is caused because the Student class does not have the method setStudentId{Long id)