hibernate关联关系问题

[k851590063]

现有RoomArea,Room,Bed,三个实体，
关系是RoomArea对应多个Room，Room对应多个Bed,
RoomArea实体中有
@OneToMany(mappedBy = "areaId")
private List<Room> rooms;

Room实体中有
private Long areaId;
@ManyToOne
@JoinColumn(insertable = false, updatable = false)
@NotFound(action = NotFoundAction.IGNORE)
private RoomArea roomArea;
@OneToMany(mappedBy = "roomId")
private List<Bed> beds;

Bed实体中
private Long roomId;
@ManyToOne
@JoinColumn(insertable = false, updatable = false)
@NotFound(action = NotFoundAction.IGNORE)
private Room room;

hibernate在生成表的时候room表生成了area_id 和room_area_id,
bed表中只生成了room_id 并没有生成bed_room_id,
为什么room表会多生成一个room_area_id，他们的一对多关系配的是一样的