a different object with the same identifier value was already associated with the session [duplicate]

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Hibernate: different object with the same identifier value was already associated with the session

I get the following error:

a different object with the same identifier value was already associated with the session

I have two types of objects, Course and RecommendedSchedule which has a set of courses. Here are their xml definitions:

<hibernate-mapping>
<class name="database.datatypes.Course" table="courses" lazy="false">
    <id name="id" column="ID">
         <generator class="assigned"/>
    </id>
    <property name="name" type="string"/>
    <property name="date"/>
</class>

and

<hibernate-mapping>
<class name="database.datatypes.RecommendedSchedule" table="recommended_schedules" lazy="false">
    <id name="id" column="ID">
         <generator class="increment"/>
    </id>
    <set name="courses" table="schedules_courses" cascade="save-update" lazy="false">
        <key column="course_id"/>
        <many-to-many class="database.datatypes.Course"/>
    </set>
    <property name="semester" type="string"/>
    <property name="path" type="string"/>
</class>

Basically if i insert two recommended systems with different sets, but using the same Course objects, it works, but if i do the exact same thing but use different Course objects (with the same values) i get the error.

Anyone knows what I'm doing wrong?

Here is an example for a piece of code that fails:

Session s = db.factory.openSession();
    Set<Course> set1 = new HashSet<>();
    Set<Course> set2 = new HashSet<>();
    Course c1 = new Course(104167L, "Algebra A");
    Course c2 = new Course(234114L, "Introduction to CS H and M");
    Course c3 = new Course(104012L, "Calculus 1 T");
    Course c4 = new Course(234145L, "Digital Systems");
    Course c12 = new Course(104167L, "Algebra A");
    Course c22 = new Course(234114L, "Introduction to CS H and M");
    Course c32 = new Course(104012L, "Calculus 1 T");
    Course c42 = new Course(234145L, "Digital Systems");
    set1.add(c1);
    set1.add(c2);
    set1.add(c3);
    set2.add(c12);
    set2.add(c22);
    set2.add(c32);
    set2.add(c42);
    RecommendedSchedule r1 = new RecommendedSchedule(set1, "General 3 years", "1");
    RecommendedSchedule r2 = new RecommendedSchedule(set2, "General 4 years", "1");
    Collection<RecommendedSchedule> col = new ArrayList<RecommendedSchedule>();
    Collection<Course> col2 = new ArrayList<Course>();
    col.add(r1);
    col.add(r2);
    col2.add(c12);
    col2.add(c22);
    col2.add(c32);
    col2.add(c42);

    Transaction t = s.beginTransaction();
    s.save(r1);
    s.save(r2);
    t.commit();
    s.close();

if i did instead:

set2.add(c1);
set2.add(c2);
set2.add(c3);
set2.add(c4);

It would've worked. (This of course isn't the real issue, but a simple example)

Answer 1

In the end i simply used merge() instead of save(), seems it solves the problem even though i have a set of objects and not just trying to work with a normal object.