Question

我正在尝试创建一个用于保存pays对象的api，问题是此对象包含另一个类Region的外键。当我创建用于保存区域对象的api时，它起作用了，但是当我要保存新的pays实例时，外键在数据库中为空。

付费类别：

@Entity
public class Pays {

@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private int id_pays;

private String pays;

private String description;

private String etat;

@ManyToOne
@JoinColumn(name="region_id")
@JsonBackReference
private Region region;

@OneToMany(mappedBy="pays",
        cascade=CascadeType.ALL,
        fetch=FetchType.EAGER)
@JsonManagedReference
private List<Zone> zone;

public int getId_pays() {
    return id_pays;
}

public void setId_pays(int id_pays) {
    this.id_pays = id_pays;
}

public List<Zone> getZone() {
    return zone;
}

public void setZone(List<Zone> zone) {
    this.zone = zone;
}

public String getPays() {
    return pays;
}

public void setPays(String pays) {
    this.pays = pays;
}

public String getDescription() {
    return description;
}

public void setDescription(String description) {
    this.description = description;
}

public String getEtat() {
    return etat;
}

public void setEtat(String etat) {
    this.etat = etat;
}

public Region getRegion() {
    return region;
}

public void setRegion(Region region) {
    this.region = region;
}

@Override
public String toString() {
    return "Pays [idpays=" + id_pays + ", pays=" + pays + ", description=" + description + ", etat=" + etat + ", region="
            + region + ", zone=" + zone + "]";
}

}

区域类别：

@Entity
public class Region {

@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private int id_Region;

private String region;

private String description;


@OneToMany(mappedBy="region", 
        cascade=CascadeType.ALL,
        fetch=FetchType.EAGER)
@JsonManagedReference
private List<Pays> pays;

public List<Pays> getPays() {
    return pays;
}
public void setPays(List<Pays> pays) {
    this.pays = pays;
}
public int getIdRegion() {
    return id_Region;
}
public void setIdRegion(int idRegion) {
    this.id_Region = idRegion;
}
public String getRegion() {
    return region;
}
public void setRegion(String region) {
    this.region = region;
}
public String getDescription() {
    return description;
}
public void setDescription(String description) {
    this.description = description;
}
public void add(Pays tempPays) {
    if (pays==null) {
        pays=new ArrayList<Pays>();
    }
    pays.add(tempPays);
    tempPays.setRegion(this);
}
@Override
public String toString() {
    return "Region [idRegion=" + id_Region + ", region=" + region + ", description=" + description + ", pays=" + pays
            + "]";
}

}

paysContoller类：

@RestController
public class PaysController {

@Autowired
private PaysService paysService;

//Get all the pays
@GetMapping("/api/pays")
public ResponseEntity<List<Pays>> list(){
    List<Pays> list = paysService.listPays();
    return ResponseEntity.ok().body(list);
}

//Save the pays
@PostMapping("/api/pays")
public ResponseEntity<?> save(@RequestBody Pays pays){
    long id = paysService.save(pays);
    return ResponseEntity.ok().body("Pays added successfully with id " + id);       
}

//Get a single record
@GetMapping("/api/pays/{id}")
public ResponseEntity<Pays> get(@PathVariable("id") int id){
    Pays pays = paysService.getPays(id);
    return ResponseEntity.ok().body(pays);
}

//Updating a record
@PutMapping("/api/pays/{id}")
public ResponseEntity<?> update(@PathVariable("id") int id, @RequestBody Pays pays){
    paysService.updatePays(id, pays);
    return ResponseEntity.ok().body("Pays has been updated.");
}

//delete a record
@DeleteMapping("/api/pays/{id}")
public ResponseEntity<?> delete(@PathVariable("id") int id){
    paysService.deletePays(id);
    return ResponseEntity.ok().body("record deleted");
}

}

JSON parse error: Cannot construct instance of `com.managem.model.Region` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('4'); nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `com.managem.model.Region` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('4') at [Source: (PushbackInputStream); line: 5, column: 13] (through reference chain: com.managem.model.Pays["region"])]

json：

{
"pays" : "USA",
"description" : "free country",
"etat" : "active",
"region_id" : 1
 }

Answer 1

我认为您的错误说明了一切

no String-argument constructor/factory method to deserialize from String value ('4');

因此，在Pays实体中，您已将region_id定义为Region对象

但是在JSON中，您正在传递"region_id" : 4

现在无法将4反序列化为Region对象

因此出现错误

要解决此问题，需要像这样的JSON。

{
    "pays" : "USA",
    "description" : "free country",
    "etat" : "active",
    "region_id" : {
        id_Region: 4,
    }
}

注意：只是一个示例，它的实际JSON密钥可能有所不同。

JSON解析错误无法构造``无字符串参数构造函数/工厂方法的实例以从字符串值（'4'）反序列化;

1 个答案: