我是Spring-boot和MongoDB的新手。在MongoDB中，两个集合之间的手动引用可以正常工作。 Spring-boot中的映射似乎不起作用。我真的不知道还要检查什么。在所有相关的详细信息下面，很长的问题对不起。

不使用DBref的原因是因为我可能需要这些投影。

“玩家”集合具有此架构（不允许其他任何形式）

{"_id":{"$oid":"5f56021d61738cc35de79438"},"name":"Romeo","entryDate":{"$date":"2020-08-23T22:00:00.000Z"}}`

“游戏”集合具有以下架构

   {
    "_id":{"$oid":"5f5614a361738cc35de7943b"},"dices":{
       "value1":1,"value2":6
     },"gameScore":1,"player_id":{"$oid":"5f56021d61738cc35de79438"}
   }

MongoDB Compass中的聚合

[{
    $match: {
        _id: ObjectId('5f56021d61738cc35de79438')
    }
},{
    $lookup: {
        from: 'games',localField: '_id',foreignField: 'player_id',as: 'games'
    }
}]

收益

在Spring-boot中，POJO为：

@Document(collection = "players")
public class Player {
    @Id
    private String id;
    private String name;
    private LocalDate entryDate= LocalDate.now();
    private List<Game> game;
    
    public Player(){};

    public Player(String name) {
        this.name = name;
    }
//getters and setters for all properties,including game
}

@Document(collection = "games")
public class Game {
    @Id
    private String id;
    private Dices dices;
    private Integer gameScore;
    @Field(value = "player_id")
    private String playerId;

    public Game(){};

    public Game(Dices dices) {
        this.dices = dices;
    }
//getters and setters for all properties
}

public class Dices {

    private int value1;
    private int value2;

    public Dices(){}

    public Dices(int value1,int value2) {
        this.value1 = value1;
        this.value2 = value2;
    }
//getters and setters for both properties

在邮递员中

获取findAll玩家显示：

[{“ id”：“ 5f56021d61738cc35de79438”，“名称”：“ Romeo”，“ entryDate”：[2020,8,24]，“ game”：null}，{“ id”：“ 5f5602e361738cc35de79439”，“ name“：” Julieta“，” entryDate“：[2020,24]，” game“：null}， ....]

显示游戏是因为我还为此属性添加了getter和setter方法，只是试图找到一种方法来正确映射游戏作为对玩家的手动引用

获取findAll游戏：

[{“ id”：“ 5f5614a361738cc35de7943b”，“ dices”：{“ value1”：1，“ value2”：6}，“ gameScore”：1，“ playerId”：“ 5f56021d61738cc35de79438”}，

{“ id”：“ 5f5619f561738cc35de7943c”，“骰子”：{“ value1”：2，“ value2”：5}，“ gameScore”：1，“ playerId”：“ 5f5602e361738cc35de79439”}，

{“ id”：“ 5f561a5461738cc35de7943d”，“骰子”：{“ value1”：3，“ value2”：3}，“ gameScore”：0，“ playerId”：“ 5f56021d61738cc35de79438”}， ...]

GET lh：8080 / players / 5f56021d61738cc35de79438 / games 产生一个空数组，这就是为什么我认为Spring-boot中的集合之间的映射失败的原因。

GamesRepository

@Repository
public interface GameRepository extends MongoRepository<Game,String> {

    List<Game> findAll();

    List<Game> findGamesByPlayerId(String playerId);

}

服务中的方法

    @Override
    public List<Game> findAllGamesByPlayerId(String playerId) {

        Optional<Player> playerDB= playerRepository.findById(playerId);

        if(playerDB.isPresent()) {
            return  gameRepository.findGamesByPlayerId(playerId);
        }

        else throw new ResourceNotFoundException("Player with id: "+playerId+" does not exist");
    }

和GameController

    @GetMapping("/{ID}/games")
    public ResponseEntity<List<Game>> getallGamesByPlayerId (@PathVariable("ID") String playerId){
        return ResponseEntity.ok()
                .body(gameService.findAllGamesByPlayerId(playerId));
    }

欢迎小贴士！