Relationship CRUD API Spring Boot - spring-boot

Question

I am creating a crud api with a many to many relationship betwen role and user. When i make a Get HTTP Request, i get the mesage below but When i delete all relationship and make findall on single table, it works percfecttly. Where do you think the problem is?
Error Message in postman
{
"timestamp": "2021-07-10T04:28:24.877+0000",
"status": 500,
"error": "Internal Server Error",
"message": "JSON mapping problem: java.util.ArrayList[0]->com.notyfyd.entity.User[\"roles\"]; nested exception is com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: com.notyfyd.entity.User.roles, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->com.notyfyd.entity.User[\"roles\"])",
"path": "/user/all"
}
Role Entity
package com.notyfyd.entity;
import com.fasterxml.jackson.annotation.JsonIdentityInfo;
import com.fasterxml.jackson.annotation.ObjectIdGenerators;
import javax.persistence.*;
import java.util.List;
#Entity
#Table(name = "t_role")
#JsonIdentityInfo(
generator = ObjectIdGenerators.PropertyGenerator.class,
property = "id")
public class Role {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private String description;
#ManyToMany(targetEntity = User.class, mappedBy = "roles", cascade = {CascadeType.PERSIST, CascadeType.DETACH,CascadeType.MERGE,CascadeType.REFRESH})
private List<User> users;
public Long getId() {
return this.id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
public String getDescription() {
return this.description;
}
public void setDescription(String description) {
this.description = description;
}
public List<User> getUsers() {
return users;
}
public void setUsers(List<User> users) {
this.users = users;
}
}
User Entity
import com.fasterxml.jackson.annotation.JsonIdentityInfo;
import com.fasterxml.jackson.annotation.ObjectIdGenerators;
import javax.persistence.*;
import java.util.List;
#Entity
#Table(name = "t_user")
#JsonIdentityInfo(
generator = ObjectIdGenerators.PropertyGenerator.class,
property = "id")
public class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String firstName;
private String lastName;
private String mobile;
#Column(unique = true)
private String email;
#ManyToMany(targetEntity = Role.class, cascade = {CascadeType.PERSIST, CascadeType.DETACH,CascadeType.MERGE,CascadeType.REFRESH} )
#JoinTable(
name="t_user_roles",
joinColumns=
#JoinColumn( name="user_id", referencedColumnName="id"),
inverseJoinColumns=#JoinColumn(name="role_id", referencedColumnName="id"))
private List<Role> roles;
public List<Role> getRoles() {
return roles;
}
public void setRoles(List<Role> roles) {
this.roles = roles;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getMobile() {
return mobile;
}
public void setMobile(String mobile) {
this.mobile = mobile;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
}
here is the log error on MSSQL Server
2021-07-10 11:20:59.333 WARN 3124 --- [nio-6120-exec-4] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: failed to lazily initialize a collection of role: fdsa.edu.PNUFDSA.Model.AnneeAcademique.paiements, could not initialize proxy - no Session; nested exception is com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: fdsa.edu.PNUFDSA.Model.AnneeAcademique.paiements, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->fdsa.edu.PNUFDSA.Model.AnneeAcademique["paiements"])]
the Entity is:
* "Visual Paradigm: DO NOT MODIFY THIS FILE!"
*
* This is an automatic generated file. It will be regenerated every time
* you generate persistence class.
*
* Modifying its content may cause the program not work, or your work may lost.
*/
/**
* Licensee:
* License Type: Evaluation
*/
package fdsa.edu.PNUFDSA.Model;
import com.fasterxml.jackson.annotation.JsonIgnore;
import lombok.Data;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import javax.persistence.*;
#Entity
#Data
//#org.hibernate.annotations.Proxy(lazy=false)
#Table(name="AnneeAcademique")
public class AnneeAcademique implements Serializable {
public AnneeAcademique() {
}
#Column(name="ID", nullable=false, length=10)
#Id
#GeneratedValue(generator="PNU_ANNEEACADEMIQUE_ID_GENERATOR")
#org.hibernate.annotations.GenericGenerator(name="PNU_ANNEEACADEMIQUE_ID_GENERATOR", strategy="native")
private int id;
#Column(name="Debut", nullable=true)
#Temporal(TemporalType.DATE)
private java.util.Date debut;
#Column(name="Fin", nullable=true)
#Temporal(TemporalType.DATE)
private java.util.Date fin;
#JsonIgnore
#ManyToMany(mappedBy="anneeAcademiques", targetEntity=fdsa.edu.PNUFDSA.Model.Cours.class)
#org.hibernate.annotations.Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE, org.hibernate.annotations.CascadeType.LOCK})
#org.hibernate.annotations.LazyCollection(org.hibernate.annotations.LazyCollectionOption.TRUE)
private java.util.Set cours = new java.util.HashSet();
#JsonIgnore
#OneToMany(mappedBy="anneeAcademique", targetEntity=fdsa.edu.PNUFDSA.Model.Paiement.class)
#org.hibernate.annotations.Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE, org.hibernate.annotations.CascadeType.LOCK})
#org.hibernate.annotations.LazyCollection(org.hibernate.annotations.LazyCollectionOption.TRUE)
private List paiements = new ArrayList();
private void setId(int value) {
this.id = value;
}
public int getId() {
return id;
}
public int getORMID() {
return getId();
}
public void setDebut(java.util.Date value) {
this.debut = value;
}
public java.util.Date getDebut() {
return debut;
}
public void setFin(java.util.Date value) {
this.fin = value;
}
public java.util.Date getFin() {
return fin;
}
public void setCours(java.util.Set value) {
this.cours = value;
}
public java.util.Set getCours() {
return cours;
}
public void setPaiements(List value) {
this.paiements = value;
}
public List getPaiements() {
return paiements;
}
public String toString() {
return String.valueOf(getId());
}
}

Answer 1

Are you returning that entity directly as json. Can add #JsonIgnore on below field.
#JsonIgnore
private List<Role> roles;

Answer 2

You can set fetch type to FetchType.EAGER on your many to many relations in your entities.
Try this and let me know what happened.