CODEWITHSUNDEEP
javahibernate
chiperortiz
chiperortiz

Reputation: 4991

Java Hibernate.merge may in any circunstance return null?

Hello i have a snippet like this.

public void update(Student student)
{
    student=super.merge(student);
    currentSession().update(student);
    return;
}

But sometimes this code throws

java.lang.IllegalArgumentException: attempt to create saveOrUpdate event with null entity.

I was wondering how is this possible merge may return null in any circunstance? 

Because i have checked Student is not null because if is null merge would throw.

Exception in thread "main" java.lang.IllegalArgumentException: attempt to create merge event with null entity

The only situation i think is happening this stuff is if merge is returning null is this possible??

Sorry if this question is simple thanks a lot a best regards from Venezuela..

Upvotes: 1

Views: 1880

Answers (1)

XLi
XLi

Reputation: 164

merge() is used to merge a detached object with an attached object (both have the same id). For example, you passed in a student1 object in method update(), which has an id and its status is detached:

public void update(Student student1)
{
    //student1 is in detached status, you may modify it if not yet done
    student1.setName("ABC");

    //now load a student2 from db with the same id, note student2 is in persistent status
    Student student2 = currentSession().load(Student.class, student1.getId());

    //merge student1 to student2 and return a new student3
    Student student3 = currentSession().merge(student1);
    //--done, checkout student3, you will see "ABC" is merged. You can't call update() in this case. 
    return;
}

If you just want to update passed in student, then remove student=super.merge(student);, call saveOrUpdate(), like this:

public void update(Student student)
{
    currentSession().saveOrUpdate(student);
    return;
}

Upvotes: 1

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