OneToMany映射在Controller Crud Spring Boot Rest API中不起作用

Question

I don't know how to solve the 500 status response by the api. I am testing with Postman.

The request

{
        "nome": "Ciencia da Computação",
        "totalCreditos": 2333,
        "professor": {
            "id": 2,
            "matricula": 0,
            "nome": "José da silva"
    }
}

How do I implement One to many relationship and expose the api the correct way for CRUD operation. I'm getting a 500 error. I don't know if I need to change the Controller functions

CursoController.java

@CrossOrigin(origins = "*")
@RestController
@RequestMapping({"/api/curso"})
public class CursoController {
    @Autowired
    private CursoService cursoService;
    private ProfessorService professorService;

    @PostMapping
    public Curso create(@RequestBody Curso curso){
        return cursoService.create(curso);
    }

    @GetMapping(path = {"/{id}"})
    public Curso findOne(@PathVariable("id") int id){
        return cursoService.findById(id);
    }

    @PutMapping
    public Curso update(@RequestBody Curso Curso){
        return cursoService.update(Curso);
    }

    @DeleteMapping(path ={"/{id}"})
    public Curso delete(@PathVariable("id") int id) {
        return cursoService.delete(id);
    }

    @GetMapping
    public List findAll(){
        return cursoService.findAll();
    }
}

Curso.java

@Entity
@Table(name = "curso")
public class Curso implements Serializable {
    @Id
    @Column
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    @Column
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long codigo;
    @Column
    private Long totalCreditos;

    @Column
    private String nome;

    @ManyToOne(fetch = FetchType.LAZY, optional = false, cascade = 
    CascadeType.PERSIST)
    @JoinColumn(name = "professor_id", nullable = false)
    @OnDelete(action = OnDeleteAction.CASCADE)
    @JsonIgnore
    @JsonManagedReference
    private Professor professor;


}

Answer 1

you should never use CascadeType.ALL on @ManyToOne since entity state transitions should propagate from Parent entities to Child ones.

Remove

(fetch = FetchType.LAZY, optional = false, cascade = 
    CascadeType.PERSIST)

from

@ManyToOne(fetch = FetchType.LAZY, optional = false, cascade = 
    CascadeType.PERSIST)

and add it in

 @OneToMany(fetch = FetchType.LAZY, optional = false, cascade = 
        CascadeType.PERSIST)

side.

Explanation :

As vladmihalcea explained in this article and in his book, High-Performance Java Persistence , you should never use CascadeType.ALL on @ManyToOne since entity state transitions should propagate from Parent entities to Child ones.

The @ManyToOne side is always the Child association since it should map the underlying FK.

Therefore, move the CascadeType.ALL from the @ManyToOne association to the @OneToMany which should use the mappedBy attribute since it's the most efficient one-to-many mapping . `

Answer 2

Can you use CascadeType.ALL whitch Cascade all operations ( PERSIST,MERGE,REMOVE,REFRESH,DETACH ). For more details you can take a look here