I have mapped a bidirectional many-to-many exception between the entities Course and Trainee in the following manner:

Course
{
    ...
    private Collection<Trainee> students;
    ...
    @ManyToMany(targetEntity = lesson.domain.Trainee.class,
        cascade = {CascadeType.All}, fetch = {FetchType.EAGER})
    @Jointable(name="COURSE_TRAINEE",
        joincolumns = @JoinColumn(name="COURSE_ID"),
        inverseJoinColumns = @JoinColumn(name = "TRAINEE_ID"))
    @CollectionOfElements
    public Collection<Trainee> getStudents() {
        return students;
        }
    ...
}


Trainee
{
    ...
    private Collection<Course> authCourses;
    ...
    @ManyToMany(cascade = {CascadeType.All}, fetch = {FetchType.EAGER},
        mappedBy = "students", targetEntity = lesson.domain.Course.class)
    @CollectionOfElements
    public Collection<Course> getAuthCourses() {
        return authCourses;
    }
    ...
}

Instead of creating a table where the Primary Key is made of the two foreign keys (imported from the table of the related two entities), the system generates the table "COURSE_TRAINEE" with the following schema:

I am working on MySQL 5.1 and my App. Server is JBoss 5.1. Does anyone guess why?