带Hibernate空间自引用的弹簧引导JPA导致循环

Question

我目前正在编写一个服务，在那里我可以用一些数据存储一个地理空间点。我有一个"dataPoint“类，如下所示：

@Entity
@Table(name = "datapoint")
public class DataPoint {
    @Id
    int dataPoint_id;

    @Column(name = "body")
    String body;

    @Column(name = "location", columnDefinition = "Geometry")
    PGgeometry location;

    @Column(name = "deleted")
    boolean deleted;

    //Getters and Setters...

我试图使用Spring通过API路径向PostGIS数据库添加一个带有一些信息的点。我已经建立了一个控制器，它看起来像这样：

@RestController
@RequestMapping(value = "/dataPoint")
public class DataPointController {

    @Autowired
    private DataPointService myPointService;

    @RequestMapping(value = "/add/{body}/{latitude}/{longitude}/")
    public DataPoint addDataPoint(@PathVariable String body, @PathVariable double latitude, @PathVariable double longitude){
        DataPoint myPoint = new DataPoint();
        myPoint.setBody(body);
        PGgeometry geometry = new PGgeometry();
        try {
            geometry.setValue("POINT("+longitude +" " + latitude+")");
            geometry.setType("POINT");
            // Debugging Stuff
            System.out.println("GEOMETRY VALUE LOOK: {{{{ " + geometry.getValue() + "   " + geometry.getType());
        } catch (SQLException e) {
            e.printStackTrace();
        }
        myPoint.setLocation(geometry);
        myPointService.saveDataPoint(myPoint);
        return myPoint;
    }

它反过来链接到一个DataPointService，它只是充当控制器之间的中间角色，saveDataPoint()看起来是这样的：

public void saveDataPoint(DataPoint myPoint) {
    dataPointRepository.save(myPoint);
}

以及DataPointRepository，它看起来是这样的：

@Repository
public interface DataPointRepository extends JpaRepository<DataPoint, Integer> {
}

但是，当我访问add链接时，会得到以下错误：

Failed to write HTTP message: org.springframework.http.converter.HttpMessageNotWritableException: Could not write content: Direct self-reference leading to cycle (through reference chain: com.testing.model.DataPoint["location"]->org.postgis.PGgeometry["geometry"]->org.postgis.Point["firstPoint"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Direct self-reference leading to cycle (through reference chain: com.testing.model.DataPoint["location"]->org.postgis.PGgeometry["geometry"]->org.postgis.Point["firstPoint"])

我在一些例子中看到了@JsonBackReference及其对偶的用法，然而，在实体被来回链接的情况下，它被使用了，我在这里没有看到这种情况，事实上，错误似乎并不是循环的，那么这里发生了什么呢？

Answer 1

我遇到了同样的问题。它是循环的，因为Point有一个字段firstPoint，它再次引用Point。我能够通过安装postgis-geojson：https://jitpack.io/p/stephenbrough/postgis-geojson来解决这个问题。