问题描述
我正在创建一个角色和用户之间具有多对多关系的 crud api。当我发出一个获取 HTTP 请求时，我得到下面的消息但是当我删除所有关系并在单个表上进行 findall 时，它完美地工作。您认为问题出在哪里？
邮递员中的错误信息
{
"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"
}
角色实体
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;
}
}
用户实体
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,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;
}
}
解决方法
您是否直接以 json.json 形式返回该实体？可以在下面的字段中添加@JsonIgnore。
@JsonIgnore
private List<Role> roles;
这里是 MSSQL Server 上的日志错误
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"])]
实体是：
* "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());
}
}
您可以将实体中的多对多关系的提取类型设置为 FetchType.EAGER。
试试这个，让我知道发生了什么。