How to add a Map in an entity class?

Question

I want to add a mapping as

Map personMap;

inside an entity class, where Person is the entity. The

Answer 1

As per section 2.7 of JSR-317, if the value of the Map is an entity (which is your case) a join table is created and then a OneToMany / ManyToOne annotation should be used.

As for the key, if it is a Basic Type, the @MapKeyColumn can be used to customize the mapping column of the key. So here is my take on your example:

@OneToMany
@MapKeyColumn(name="person_nickname")
Map<String, Person> personMap;

EDITED:

After some testing, the following seems to work pretty well:

@ElementCollection
@CollectionTable(name="<name_of_join_table>")
@MapKeyColumn(name="<name_of_map_key_in_table>")
Map<String, Person> personMap;

The above generates a join table with three fields: one for the mapping holder id, one for the key and one for the value.