如何在mongoDB中执行联接查询

Question

我已经在 SQL 中完成了此操作，以获取parentName作为对parentId的响应。

public class FolderStructure extends CommonAttribute implements Serializable {

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

@JsonIgnore
@ManyToOne
@JoinColumn(name = "parentid")
private FolderStructure parent;

@Transient
private Long parentid;

@Transient
private String parentName;


@JsonIgnore
@OneToMany(mappedBy = "parent", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<FolderStructure> childFolder = new HashSet();

public void setParentid() {
    if (parent != null && parent.getFolderId() > 0) {
        this.parentid = parent.getFolderId();
    }

}

public void setParentName() {
    if (parent != null && parent.getFolderId() > 0
            && parent.getFolderName() != null) {
        this.parentName = parent.getFolderName();
    }

}

我收到如下响应，{ folderId: 4, folderName: "BATTERY LOG", parentid: 1, parentName: "Engine", folderType: "custom" }

我正在尝试使用 mongoDB 通过添加relmongo依赖性来执行相同的代码。但是我不明白如何在mongoDB中连接两列。这是我的模特

@EnableRelMongo
@Document(collection = "folderstructure")
public class FolderStructure
{

@JsonIgnore
@JoinProperty(name = "parentid")
private FolderStructure parent;

@Field("parentid")
private Long parentid;

@Transient
private String parentName;

@JsonIgnore
@OneToMany( fetch=FetchType.EAGER, cascade = CascadeType.PERSIST)
@JoinProperty(name = "parent")
private Set<FolderStructure> childFolder = new HashSet();

这是我的控制器，

 @GetMapping("")
  public String getAllFolders() {
     String res = "";
        try {
            JSONObject jsonobj = new JSONObject();
            List<FolderStructure> folderlst = folderDao.findAll();
            List<FolderStructure> folderlstRes = new ArrayList<FolderStructure>();
            for (FolderStructure folder : folderlst) {
                folder.setParentid();
                folder.setParentName();
                folderlstRes.add(folder);
            }

            if (folderlstRes != null && folderlstRes.size() > 0) {
                ObjectMapper mapperObj = new ObjectMapper();
                String Detail = mapperObj.writeValueAsString(folderlstRes);
                jsonobj.put("data", new JSONArray(Detail));
                jsonobj.put("responsecode", 200);
                jsonobj.put("message", "Success");
                jsonobj.put("timestamp", new Date());
            } else {
                jsonobj.put("responsecode", 404);
                jsonobj.put("message", "Record Not Found");
                jsonobj.put("timestamp", new Date());
            }
            res = jsonobj.toString();
        } catch (JSONException | JsonProcessingException ex) {
            CampbellResponse derr = new CampbellResponse(500, new Date(), "JSON parsing exception occurred.");
            res = derr.toString();
            ex.printStackTrace();
        } catch (Exception ex) {
            CampbellResponse derr = new CampbellResponse(500, new Date(), "Exception is occurred.");
            res = derr.toString();
            ex.printStackTrace();
        }
        return res;
  }

但是我得到的是parentName作为响应。