如何使用一对多单向删除两个表之间的关系

Question

I have two entities bound with one-to-many relationship. But one entity can exist without the other. So the relationship is uni-directional. As this;

@Entity
public class TransportationOrderProduct  {

    @OneToMany(fetch = FetchType.EAGER,cascade = CascadeType.ALL)
    private List<WarehousePackage> selectedWarehousePackages;
}

@Entity
public class WarehousePackage{
}

And hibernate created these tables;

TransportationOrderProduct

• id

TransportationOrderProductSelectedWarehousePackages

• transportationOrderProductId
• selectedWarehousePackageId

WarehousePackage

• id

When fetching the collection (selectedWarehousePackages) everything works fine. But when I clear the TransportationOrderProduct.selectedWarehousePackages list, and add new ones, Hibernate throws DuplicateEntry exception. Saying that transportationOrderProductId in the TransportationOrderProductSelectedWarehousePackages table cannot be inserted twice.

I think this is because Hibernate doesn't delete the relation in the TransportationOrderProductSelectedWarehousePackages table when I call;

TransportationOrderProduct.selectedWarehousePackages.clear()

And add some entities after ;

TransportationOrderProduct.selectedWarehousePackages.add(newPackage)
TransportationOrderProduct.selectedWarehousePackages.add(newPackage)
.
.

Can somebody help?

Answer 1

Its sounds the relation is one-Many as I understand

Don't use unidirectional one-to-many associations

avoid unidirectional one-to-many associations in your domain model. Otherwise, Hibernate might create unexpected tables and execute more SQL statements than you expected and this certainly described why hibernate create 3 entities while your implementation should be 2 entities with relation one-2-many.

The definition of uni-directional sounds not an issue in our case if we use directional it's OKAY it will serve our purpose you just need attribute to map our association

using annotation

@Entity
public class TransportationOrderProduct  {
   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   @Column(name = "id")
   private long id; 

@OneToMany(fetch = FetchType.EAGER,cascade = CascadeType.ALL)
    private Set<WarehousePackage> packages= new HashSet<>();

public Set<WarehousePackage> getPackages() {
    return packages;
}

public void setPackages(Set<WarehousePackage> packages) {
    this.packages = packages;
}

public void addPackages (WarehousePackage value) {
this.packages.add(value);
} 

public void clearPackages (WarehousePackage value) {
    this.packages.clear();
} 
    ...
} 

@Entity
public class WarehousePackage{
   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   @Column(name = "id")
   private long id; 
}

You can save transportation order with association you need

TransportationOrderProduct transportation = new TransportationOrderProduct  ();

Set<WarehousePackage> packages = new HashSet <> () ; 
WarehousePackage package1 = new WarehousePackage () ;
WarehousePackage package2 = new WarehousePackage () ;
packages.add(package1);
packages.add(package2);
transportation.setPackages(packages) ;

session.save(transportation);