Spring data JPA and hibernate detached entity passed to persist on ManyToMany relationship

Question

I am trying to persist an object that has a many-to-many relationship with other objects already persisted.

Here is my persisted object (they are already persisted i

Answer 1

You need to ensure both side of the relationship are properly maintained in your code.

Update Reservation as below and then add the corresponding methods to Product.

@Entity
@Table(name = "RESERVATION")
public class Reservation {

    private int reservationId;

    private Set products = new HashSet(0);

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public int getReservationId() {
        return reservationId;
    }

    public void setReservationId(int reservationId) {
        this.reservationId = reservationId;
    }

    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinTable(name = "product_reservation", joinColumns = { @JoinColumn(name = "reservationId", nullable = false, updatable = false) }, inverseJoinColumns = { @JoinColumn(name = "productId", 
            nullable = false, updatable = false) })
    public Set getProducts() {

        //force clients through our add and remove methods
        return Collections.unmodifiableSet(products);
    }

    public void addProduct(Product product){

        //avoid circular calls : assumes equals and hashcode implemented
        if(! products.contains(product){
            products.add(product);

            //add method to Product : sets 'other side' of association
            product.addReservation(this);
        }
    }

    public void removeProduct(Product product){

        //avoid circular calls: assumes equals and hashcode implemented: 
        if(product.contains(product){
            products.remove(product);

            //add method to Product: set 'other side' of association: 
            product.removeReservation(this);
        }
    }
}

And in Products:

public void addReservation(Reservation reservation){

    //assumes equals and hashcode implemented: avoid circular calls
    if(! reservations.contains(reservation){
        reservations.add(reservation);

        //add method to Product : sets 'other side' of association
        reservation.addProduct(this);
    }
}

public void removeReservation(Reservation reservation){

    //assumes equals and hashcode implemented: avoid circular calls
    if(! reservations.contains(reservation){
        reservations.remove(reservation);

        //add method to Product : sets 'other side' of association
        reservation.reomveProduct(this);
    }
}

Now you should be able to call save on either Product or Reservation and everything should work as expected.