java - Apache OpenJPA - 仅当数据库中不存在时插入元组

Question

您好 stackoverflow 社区。

我想知道，OpenJPA 是否有可能在插入之前首先检查对象是否已存在于数据库中。

我有两个类(class):

imports...

@Entity(name="Player")
public class Player {
    private long id;
    private String nickName;
    private Team team; /* A Player is on a Team */

    @ManyToOne(cascade=CascadeType.PERSIST)
    @JoinColumn(name = "team_id")
    public Team getTeam() {
        return team;
    }

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    public long getId() {
        return id;
    }

    /* more getters / setters ...*/
}
@Entity(name="Team")
public class Team {
    private long id;
    private String name;
    private List<Player> players; /* A Team Has Players */

    @OneToMany(mappedBy = "team", targetEntity = Player.class, 
            fetch = FetchType.EAGER, cascade = CascadeType.PERSIST)
    public List<Player> getPlayers() {
        return players;
    }

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    public long getId() {
        return id;
    }

如果我想添加一个新的玩家或团队，JPA 应首先检查该玩家或团队是否已在数据库中。 如果是，则应使用现有单元的主/外键。

这可能吗？还是我需要编写自己的方法？

致以诚挚的问候 投票

Answer 1

您可能想检查此开关: http://openjpa.apache.org/builds/2.2.0/apache-openjpa/docs/jpa_2.2.html#jpa_2.2_cascadePersist

我猜您正在使用 OpenJPA 2.2.0。