@ManyToMany: Howto delete associations ?
Does anybody know, how to remove a ManyToMany relationship ?
I've experimented with the follwoing case:
@Entity
@Table (name="products")
public class A_Product implements Serializable {
private int id;
A_Product() {}
@Column (name ="products_id", nullable=false)
@Id(generate = GeneratorType.IDENTITY)
public int getId() { id }
void setId(int id) { this.id = id; }
@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE},
fetch = FetchType.LAZY, mappedBy="products")
public Collection<A_Category> getCategories() { return categories; }
void setCategories(Collection<A_Category> categories) { this.categories = categories; }
}
@Entity
@Table(name="categories")
public class A_Category implements Serializable {
private int id;
@Id(generate = GeneratorType.IDENTITY)
@Column(name="categories_id", nullable=false)
public int getId() { return this.id; }
public void setId(int id) { this.id = id; }
@ManyToMany(cascade = { CascadeType.PERSIST, CascadeType.MERGE },
fetch = FetchType.EAGER)
@AssociationTable(table = @Table(name="products_to_categories"),
joinColumns = {
@JoinColumn(name="categories_id", referencedColumnName="categories_id")
},
inverseJoinColumns = {
@JoinColumn(name="products_id", referencedColumnName="products_id")
})
public Collection<A_Product> getProducts() { return products; }
void setProducts(Collection<A_Product> products) { this.products = products; }
}
@Stateless
class ProductManager {
@Inject
private EntityManager manager;
// ...
@TransactionAttribute(value = TransactionAttributeType.REQUIRES_NEW)
public void delete(A_Product product, String clientID) {
if (product == null) { return false; }
manager.refresh(product);
Collection<A_Category> cats = product.getCategories();
for (A_Category c : cats) {
c.getProducts().remove(product);
manager.merge(c);
}
manager.remove(product);
}
}
But unfortunately, this doesn't work :(. So I'tried to directly manipulate the assoc. table with
Query q = manager.createQuery("DELETE FROM products_to_categories ptc "
+ "WHERE ptc.products_id=:id").setParameter("id", product.getId());
q.executeUpdate();
but here I get an "unsupported" exception.
So how can one remove a relationship from the association table (cascading.all is obviously not possible)?
