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3.4.6.2.4. Bag with primary key

Another interesting feature is the ability to define a surrogate primary key to a bag collection. This remove pretty much all of the drawbacks of bags: update and removal are efficient, more than one EAGER bag per query or per entity. This primary key will be contained in a additional column of your collection table but will not be visible to the Java application. @CollectionId is used to mark a collection as id bag, it also allow to override the primary key column(s), the primary key type and the generator strategy. The strategy can be identity, or any defined generator name of your application. 
@Entity
@TableGenerator(name="ids_generator", table="IDS")
public class Passport {
    ...

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name="PASSPORT_VISASTAMP")
    @CollectionId( columns = @Column(name="COLLECTION_ID"), type=@Type(type="long"), generator = "ids_generator" )
    private Collection<Stamp> visaStamp = new ArrayList();
    ...
}
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