Hibernate many-to-many infinite recursion

Question

I have a many-to-many table between Employees - SchoolDepartment EmployeeSchoolDepartment

But I could not manage to solve recursion between them. I could ignore the Set but i dont want to do it i want to show the list without recursion.

Here is the entity files :

Employee :

@Id
@Column(name="`UserId`",nullable=false)
private int userId;

@Column(name="`FirstName`",nullable=false)
private String firstName;

@Column(name="`LastName`",nullable=false)
private String lastName;


@Column(name="`NationalityId`",unique=true,nullable=false)
private String nationalityId;

@Column(name="`BirthOfDate`",nullable=false)
private Date birthOfDate;

@OneToOne(fetch = FetchType.LAZY)   
@JoinColumn(name="`UserId`")
private User user;

@OneToMany(mappedBy="employee")
@JsonIgnore()
Set<EmployeeSchoolDepartment> employeeSchoolDepartments;

SchoolDepartment

  @Id()
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   @Column(name = "id")
   private int id;
   
   
   @Column(name = "department",nullable = false)
   private String department;
   
   @ManyToOne()
   @JoinColumn(name =  "school_id")
   private School school;
   
   
   @OneToMany(mappedBy="schoolDepartment")
   Set<EmployeeSchoolDepartment> employeeSchoolDepartments;

EmployeeSchoolDepartment

@EmbeddedId
EmployeeSchoolDepartmentId id;

@Column(name = "start_date")
private Date startDate;

@Column(name = "graduate_date")
private Date graduateDate;



@ManyToOne()
@MapsId("employee_id")
@JoinColumn(name="employee_id")
private Employee employee;

@ManyToOne()
@MapsId("school_deparment_id")
@JoinColumn(name="school_department_id")
private SchoolDepartment schoolDepartment;

Answer 1

You need to change EmployeeSchoolDepartment.

@MapsId is not correct in this case because it only works if the value of the association can be used as an id. In this case you need a composite id because is the combination of the two associations that makes the id.

You can pick one of these two approaches:

1. Composite identifiers with @IdClass:

@Entity
@IdClass(EmployeeSchoolDepartmentId.class)
class EmployeeSchoolDepartment {

    @Id
    @ManyToOne
    @JoinColumn(name="employee_id")
    private Employee employee;

    @Id
    @ManyToOne
    @JoinColumn(name="school_department_id")
    private SchoolDepartment schoolDepartment;

    @Column(name = "start_date")
    private Date startDate;

    @Column(name = "graduate_date")
    private Date graduateDate;

}

class EmployeeSchoolDepartmentId implements Serializable {

    private Employee employee;

    private SchoolDepartment schoolDepartment;

    public EmployeeSchoolDepartmentId(Employee employee, SchoolDepartment schoolDepartment) {
        this.employee = employee;
        this.schoolDepartment = schoolDepartment;
    }

    private EmployeeSchoolDepartmentId() {
    }

    //Getters and setters are omitted for brevity
}

2. Composite identifiers with @EmbeddedId:

@Entity
class EmployeeSchoolDepartment {

    @EmbeddedId
    EmployeeSchoolDepartmentId id;

    @Column(name = "start_date")
    private Date startDate;

    @Column(name = "graduate_date")
    private Date graduateDate;
}

@Embeddable
class EmployeeSchoolDepartmentId implements Serializable {

    @ManyToOne
    @JoinColumn(name="employee_id")
    private Employee employee;

    @ManyToOne
    @JoinColumn(name="school_department_id")
    private SchoolDepartment schoolDepartment;

    public EmployeeSchoolDepartmentId(Employee employee, SchoolDepartment schoolDepartment) {
        this.employee = employee;
        this.schoolDepartment = schoolDepartment;
    }

    private EmployeeSchoolDepartmentId() {
    }

    //Getters, setters, hashcode and equals are omitted for brevity
}