Question

我有一个类需要管理另外两个类的映射，但我需要将它隔离到它关心的记录。基本上，您有一个可能在任意数量的游戏服务器上拥有帐户的玩家。每个服务器必须仅管理其服务器的播放器到帐户映射。在这些存根类中，我省略了许多不必要的字段。假设

// player has no collections or associations in the class
public class Player {
    @Id @GeneratedValue @Column private int id;
    // other crap about the actual person
}

// character has an association to the player and the server
public class LocalCharacter {
    @Id @GeneratedValue @Column private int id;
    @ManyToOne private Player player;
    @ManyToOne private GameServer server;
    // other crap about this person's character on this server
}

// game server needs to know who all is on it, but it needs to be mapped to the player
public class GameServer {
    @Id @GeneratedValue @Column private int id;
    @/* no idea here */ private Map<Player, LocalCharacter> localCharacters;
}

我不确定如何构建此映射。我知道如果我只想要一个Set<LocalCharacter>我可以用@OneToMany做到这一点。我知道我可以在玩家身上做join fetch并自己构建地图，但这似乎很蹩脚 - 我希望冬眠来为我做！ :-)我怎样才能实现这一目标？

Answer 1

您需要使用@MapKeyJoinColumn：

public class GameServer {

    @Id 
    private Integer id;

    @OneToMany(mappedBy="server")       
    @MapKeyJoinColumn(name="player_id")
    private Map<Player, LocalCharacter> localCharacters = new HashMap<>();

}

检查此答案以获取various java.util.Map associations的详细说明。

如何注释地图以加入两个看似无关的类？

1 个答案: