How to populate back reference while binding nested autogrown list?
Preface
I've got a classical Parent-Child problem. Here's the code:
Code:
@Entity
public class Supply {
@OneToMany(cascade = { CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH, CascadeType.DETACH }, mappedBy = "supply")
private List<SupplyItem> items = new ArrayList<SupplyItem>();
// Getters/Setters and id field
}
@Entity
public class SupplyItem {
@NotNull
@ManyToOne
private Supply supply;
private Integer quantity;
// Getters/Setters and id field
}
When I'm trying to save a bean tree in one go:
Code:
Supply supply = new Supply();
SupplyItem item = new SupplyItem();
supply.getItems().add(item);
entityManager.persist(supply);
Naturally I get ConstraintViolationException since I have validation configured and item.supply is null.
Hibernate in Action suggests the following approach:
Code:
public class Supply {
// Skipped
public void addItem(SupplyItem item) {
item.setSupply(this);
items.add(item);
}
// Skipped
}
Supply supply = new Supply();
SupplyItem item = new SupplyItem();
supply.addItem(item);
entityManager.persist(supply);
Problem
The problem is that I don't populate items by hand, thus I cannot use a helper addItem() method. Instead I get my supply object constructed via web binding. The items list is populated by means of list autogrowing facility.
So my view markup looks like this:
HTML Code:
<form:form modelAttribute="supply">
<!-- Other supply fields -->
<form:input path="items[0].quantity" />
<form:input path="items[1].quantity" />
</form:form>
I know that I could iterate over all the supply items and set the back reference to supply, but that looks like a hack to me.
So I wonder is there any other way to make binder/expression parser/whatever to do that for me :)? Maybe I could provide the factory method for supply items creation somehow?
If that matters I use WebFlow, but I would like to know whether it is possible for MVC too.
