处理一对多和多对一映射的问题

Question

the problem is when i add sous_categorie for a categorie that already exists an exception appears

java.sql.SQLIntegrityConstraintViolationException: Le champ 'id_cat' ne peut être vide (null)

i used postman for testing the API

{
"id_Cat": "1274d819-ca54-455b-b69f-07a3f8b345c0",
"souCatName": "hospitals"
}

Class DBCategorie

@Entity
@Table(name = "categorie")
public class DBCategorie {
@Id
@GeneratedValue(generator = "uuid2")
@GenericGenerator(name = "uuid2", strategy = "uuid2")
private String idCat;

private String catName;

@OneToMany(mappedBy = "categorie")
private List<DBSousCategorie> souscategorie;

public DBCategorie() {
}
//getters& setter

public DBCategorie(String idCat, String catName, List<DBSousCategorie> souscategorie) {
    super();
    this.idCat = idCat;
    this.catName = catName;
    this.souscategorie = souscategorie;
}

public DBCategorie(String idCat, String catName) {
    this.idCat = idCat;
    this.catName = catName;
}

class DBSousCategorie

@Entity
@Table(name = "souscategorie")
public class DBSousCategorie {
@Id
@GeneratedValue(generator = "uuid2")
@GenericGenerator(name = "uuid2", strategy = "uuid2")
private String idSouCat;

private String souCatName;

@ManyToOne(cascade=CascadeType.ALL)
@JoinColumn(name="id_Cat")
private DBCategorie categorie;

@OneToMany(mappedBy = "souscategorie")
private List<DBFile> files;

public DBSousCategorie() {
}

//Getters & Setters

public DBSousCategorie(String idSouCat, String souCatName, DBCategorie categorie) {
    super();
    this.idSouCat = idSouCat;
    this.souCatName = souCatName;
    this.categorie = categorie;
}

Answer 1

Did you set the parent categorie object to sous_category before persisting?

dbSousCategory.setCategory(categorie);
subCategoryService.save(dbSousCategory);

And to avoid recursion use @JsonIgnore to ignore the parent category.

@Entity
@Table(name = "souscategorie")
public class DBSousCategorie {
@Id
@GeneratedValue(generator = "uuid2")
@GenericGenerator(name = "uuid2", strategy = "uuid2")
private String idSouCat;

private String souCatName;

@ManyToOne(cascade=CascadeType.ALL)
@JoinColumn(name="id_Cat")
@JsonIgnore
private DBCategorie categorie;

@OneToMany(mappedBy = "souscategorie")
private List<DBFile> files;

public DBSousCategorie() {
}

//Getters & Setters

public DBSousCategorie(String idSouCat, String souCatName, DBCategorie categorie) {
    super();
    this.idSouCat = idSouCat;
    this.souCatName = souCatName;
    this.categorie = categorie;
}