Duplicate entry for key 'PRIMARY' in JPA/Hibernate

Question

I have a many-to-many relation in a mysql database (Module - <Module_has_Subject> - Subject). Entites were generated by Eclipse, I added the method add in both classes. I use JBoss AS7/Hibernate. When I call the persist method in EJB, I get

org.hibernate.exception.ConstraintViolationException: Duplicate entry '3' for key 'PRIMARY'

I know it must be a trivial mistake, but I just don't see it. I went through most related problems here on StackOverflow and RoseIndia (I added cascade, targetEntity,...) and still without success. Entities for tables are as such:

Module.java

@Entity
@Table(name="Module")
public class Module implements Serializable {

@Id
@Column(unique=true, nullable=false)
private int idModule;

//bi-directional many-to-many association to Subject
@ManyToMany(mappedBy="modules", fetch=FetchType.EAGER,targetEntity=entity.Subject.class,cascade=CascadeType.ALL)
private List<Subject> subjects;

public void addSubject(Subject subject) {
    if(subject.getModules() == null) {
        subject.setModules(new ArrayList<Module>());
    }
    if(getSubjects() == null) {
        setSubjects(new ArrayList<Subject>());
    }
    if (!getSubjects().contains(subject)) {
        getSubjects().add(subject);
    }
    if (!subject.getModules().contains(this)) {
        subject.getModules().add(this);
    }
}
...}

Subject.java

@Entity
@Table(name="Subject")
public class Subject implements Serializable {

    @Id
    @Column(unique=true, nullable=false)
    private int idSubject;

    //bi-directional many-to-many association to Module
    @ManyToMany(fetch=FetchType.EAGER, targetEntity=entity.Module.class,cascade=CascadeType.ALL)
    @JoinTable(
        name="Module_has_Subject"
        , joinColumns={
            @JoinColumn(name="Subject_idSubject", nullable=false, referencedColumnName="idSubject")
            }
        , inverseJoinColumns={
            @JoinColumn(name="Module_idModule", nullable=false, referencedColumnName="idModule")
            }
        )
    private List<Module> modules;

    public void addModule(Module module) {
        if(getModules() == null) {
            setModules(new ArrayList<Module>());
        }
        if(module.getSubjects() == null) {
            module.setSubjects(new ArrayList<Subject>());
        }

        if (!getModules().contains(module)) {
            getModules().add(module);
        }
        if (!module.getSubjects().contains(this)) {
            module.getSubjects().add(this);
        }
    }
    ...}

SubjectEJB.java

...
Subject subject = new Subject();
for(Module module : subjectModules) {
  subject.addModule(module);
}
em.persist(subject);
em.flush();
...

Answer 1

I don't know if you managed to solve your problem yet, but I have just had exactly the same problem.

In my @OneToMany mapping I used CascadeType.ALL which resulted in 2 records being saved when I attempted to save the entity. (duplicated data, different ID's)

After scrolling on the web, I found this http://forums.codeguru.com/showthread.php?t=511992, so I changed from CascadeType.ALL to {CascadeType.PERSIST, CascadeType.MERGE}, which caused the error you have:

"ConstraintViolationException: Duplicate entry '9-2-2012-05-30' for key 'PlayerId'"

Finally I removed CascadeType.MERGE and was left with CascadeType.PERSIST which fixed the duplicate entry error and the duplicated records.

As a point, if I use just CascadeType.MERGE or just CascadeType.PERSIST, I get no errors and no duplicated data

Maybe try with CascadeType.MERGEand CascadeType.PERSIST, if you get errors, try with just CascadeType.MERGE.

It is not ideal, but hope it helps.

Chris