Question

I’m using Hibernate to store a data model, which has a number of simple fields:

@Entity
public class Shape extends DomainObject {

    @LazyCollection(LazyCollectionOption.FALSE)
    @CollectionOfElements()
    private List<Shape> children;

    @Column
    private int numSides;

    ... etc. ...
}

The DomainObject superclass keeps track of the Long id.

We’d like to make a change to the children List, so that instead of being a simple List, it’s actually a Map where the key is the Long id (from the superclass).

@???
private Map<Long, Shape> children;

How are migrations/type changes of this nature handled in Hibernate? I’m not too familiar with this aspect of Hibernate – is there some method that can be overloaded to accept the List<Shape> (on the first load of the application, using the older data) and perform a manual generation of the new Map?

Answer 1

There shouldn’t be any difference in the database: you just choose to use a Map rather than a List to store the Shapes, but the attributes of the Shape entity stay identical and thus the table storing the shapes also has the same columns.