OneToMany和JoinColumn注释是分开的

Question

I'm using hibernate 3.2.1. In an entity class I've seen the annotations @OneToMany and @JoinColumns are always used together. But what do these mean in separate? For instance what it would mean if we annotated our entity class as follows:

@Entity
@Table(name = "player_account")
public class PlayerAccount {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id;

    @ManyToOne(targetEntity = Player.class, fetch = FetchType.EAGER) 
    //Without @JoinColumn
    private Player player;

    //GET, SET
}

Answer 1

Please see what says Hibernate documentation about it: http://docs.jboss.org/hibernate/annotations/3.5/reference/en/html_single/ You need 2.2.5.2. Many-to-one section: The @JoinColumn attribute is optional, the default value(s) is like in one to one, the concatenation of the name of the relationship in the owner side, _ (underscore), and the name of the primary key column in the owned side.

Answer 2

@OneToMany annotation defines a many-valued association with one-to-many multiplicity. If the collection is defined using generics to specify the element type, the associated target entity type need not be specified; otherwise the target entity class must be specified

@JoinColumn is used to specify a mapped column for joining an entity association.