I have two tables [1]users and [2] employee_group
I am trying to implement ManyToMany relationship and this is how I implemented using annotation
@Entity
@Table(name = "employee_group")
public class EmployeeGroup {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "ID")
private long id;
@ManyToMany(mappedBy = "employeeGroups")
private List<User> users;
.........
// other properties
}
@Entity
@Table(name = "users")
public class User{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "ID")
private long id;
@ManyToMany
@JoinTable(name = "emp_group_map",
joinColumns = { @JoinColumn(name = "fk_user") },
inverseJoinColumns = { @JoinColumn(name = "fk_emp_group") })
private List<EmployeeGroup> employeeGroups;
.........
// other properties
}
Expectation: I have one user (for example: userId 100) and two employee groups in which this user belongs, so I am expecting that when I try to get this user by userId saay 100 it will get user details with employee group list and this employeeGroups will be having two records.
Issue: This returns nested results like:
{
"id": 11,
"employeeGroups": [
{
"id": 1,
"users": [
{
"id": 11,
"employeeGroups": [
{
"id": 1,
"users": [
{
"id": 11,
"employeeGroups": [
{
"id": 1,
"users": [
{
"id": 11,
"employeeGroups": [
{
"id": 1,
"users": [
{
"id": 11,
I stuck here and not getting that exactly what is wrong. I am using Spring-Boot 2.6.4.
CodePudding user response:
Jackson will be going in to User
, sees the employeeGroup
so it goes in to that, which has a List<User>
so it starts to go over those, again getting the user, then its employee group etc.
This leads to the potential OOM.
@JsonManagedReference
@JsonBackReference
may be of use to you.
Also, consider using a DTO as I am assuming you are trying to return a user out of a controller (so jackson will map it).
Using a DTO Data Transfer Object
, you will de-couple the entity and the returned DTO from the controller and also more easily customise and handle what is returned and the structure of it.