Java 许多JPA获取
嗨,我在从志愿者那里获取技能时遇到了问题。由于某些原因,我在使用此方法时无法获得列表Java 许多JPA获取,java,orm,jpa,eclipselink,Java,Orm,Jpa,Eclipselink,嗨,我在从志愿者那里获取技能时遇到了问题。由于某些原因,我在使用此方法时无法获得列表 public Volunteer getVolunteer(int id){ Volunteer vo; Query q; q = em.createNamedQuery("Volunteer.findById").setParameter("id", id); vo = (Volunteer) q.getSingleResult(); for(Skill s: vo.getSkills())
public Volunteer getVolunteer(int id){
Volunteer vo;
Query q;
q = em.createNamedQuery("Volunteer.findById").setParameter("id", id);
vo = (Volunteer) q.getSingleResult();
for(Skill s: vo.getSkills()){
System.out.println(s);
}
return vo;
}
列表为空,因此抓取似乎不起作用
我在使用JPA Eclipselink和Glassfish
感谢您的帮助
技能实体:
@Entity
@Table(name="skill")
@NamedQueries({
@NamedQuery(name = "Skill.findAll", query = "SELECT s FROM Skill s"),
@NamedQuery(name = "Skill.findById", query = "SELECT s FROM Skill s WHERE s.id = :id"),
@NamedQuery(name = "Skill.findBySkillDescription", query = "SELECT s FROM Skill s WHERE s.skillDescription = :skillDescription")})
public class Skill implements Serializable {
@Override
public String toString() {
return "Skill [id=" + id + ", skillDescription=" + skillDescription
+ "]";
}
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(unique=true, nullable=false)
private int id;
@Column(name="skill_description", length=130)
private String skillDescription;
//bi-directional many-to-many association to Volunteer
@ManyToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
@JoinTable(
name="skill_volunteer"
, joinColumns={
@JoinColumn(name="skill_id", nullable=false)
}
, inverseJoinColumns={
@JoinColumn(name="volunteer_id", nullable=false)
}
)
private List<Volunteer> volunteers;
public Skill() {
}
public int getId() {
return this.id;
}
public void setId(int id) {
this.id = id;
}
public String getSkillDescription() {
return this.skillDescription;
}
public void setSkillDescription(String skillDescription) {
this.skillDescription = skillDescription;
}
public List<Volunteer> getVolunteers() {
return this.volunteers;
}
public void setVolunteers(List<Volunteer> volunteers) {
this.volunteers = volunteers;
}
}
@Entity
@Table(name="volunteer")
@NamedQueries({
@NamedQuery(name = "Volunteer.findAll", query = "SELECT v FROM Volunteer v"),
@NamedQuery(name = "Volunteer.findById", query = "SELECT v FROM Volunteer v WHERE v.id = :id"),
@NamedQuery(name = "Volunteer.findByPhone", query = "SELECT v FROM Volunteer v WHERE v.phone = :phone"),
@NamedQuery(name = "Volunteer.findByEmail", query = "SELECT v FROM Volunteer v WHERE v.email = :email"),
@NamedQuery(name = "Volunteer.findByFirstName", query = "SELECT v FROM Volunteer v WHERE v.firstName = :firstName"),
@NamedQuery(name = "Volunteer.findByLastName", query = "SELECT v FROM Volunteer v WHERE v.lastName = :lastName")})
public class Volunteer implements Serializable {
@Override
public String toString() {
return "Volunteer [id=" + id + ", email=" + email + ", firstName="
+ firstName + ", lastName=" + lastName + ", phone=" + phone
+ "]";
}
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(unique=true, nullable=false)
private int id;
@Column(length=255)
private String email;
@Column(name="first_name", length=255)
private String firstName;
@Column(name="last_name", length=255)
private String lastName;
@Column(length=255)
private String phone;
//bi-directional many-to-many association to Event
@ManyToMany(mappedBy="volunteers")
private List<Event> events;
//bi-directional many-to-many association to Skill
@ManyToMany(mappedBy="volunteers", cascade=CascadeType.ALL, fetch=FetchType.EAGER)
private List<Skill> skills;
public Volunteer() {
}
public int getId() {
return this.id;
}
public void setId(int id) {
this.id = id;
}
public String getEmail() {
return this.email;
}
public void setEmail(String email) {
this.email = email;
}
public String getFirstName() {
return this.firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return this.lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getPhone() {
return this.phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
public List<Event> getEvents() {
return this.events;
}
public void setEvents(List<Event> events) {
this.events = events;
}
public List<Skill> getSkills() {
return this.skills;
}
public void setSkills(List<Skill> skills) {
this.skills = skills;
}
}
@实体
@表(name=“skill”)
@命名查询({
@NamedQuery(name=“Skill.findAll”,query=“从技能s中选择s”),
@NamedQuery(name=“Skill.findById”,query=“从Skill s中选择s,其中s.id=:id”),
@NamedQuery(name=“Skill.findBySkillDescription”,query=“从技能s中选择s,其中s.skillDescription=:skillDescription”)}
公共类技能实现可序列化{
@凌驾
公共字符串toString(){
return“Skill[id=“+id+”,skillDescription=“+skillDescription
+ "]";
}
私有静态最终长serialVersionUID=1L;
@身份证
@GeneratedValue(策略=GenerationType.IDENTITY)
@列(unique=true,nullable=false)
私有int-id;
@列(name=“skill\u description”,长度=130)
私有字符串技术描述;
//双向多对多协会志愿者
@ManyToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
@可接合(
name=“技能\志愿者”
,连接柱={
@JoinColumn(name=“skill\u id”,nullable=false)
}
,反向连接列={
@JoinColumn(name=“志愿者id”,null=false)
}
)
私人名单志愿者;
公共技能(){
}
公共int getId(){
返回此.id;
}
公共无效集合id(内部id){
this.id=id;
}
公共字符串getSkillDescription(){
返回此.skillDescription;
}
public void setSkillDescription(字符串skillDescription){
this.skillDescription=skillDescription;
}
公开名单{
把这个还给志愿者;
}
公众志愿者(列出志愿者){
这个。志愿者=志愿者;
}
}
和志愿者实体:
@Entity
@Table(name="skill")
@NamedQueries({
@NamedQuery(name = "Skill.findAll", query = "SELECT s FROM Skill s"),
@NamedQuery(name = "Skill.findById", query = "SELECT s FROM Skill s WHERE s.id = :id"),
@NamedQuery(name = "Skill.findBySkillDescription", query = "SELECT s FROM Skill s WHERE s.skillDescription = :skillDescription")})
public class Skill implements Serializable {
@Override
public String toString() {
return "Skill [id=" + id + ", skillDescription=" + skillDescription
+ "]";
}
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(unique=true, nullable=false)
private int id;
@Column(name="skill_description", length=130)
private String skillDescription;
//bi-directional many-to-many association to Volunteer
@ManyToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
@JoinTable(
name="skill_volunteer"
, joinColumns={
@JoinColumn(name="skill_id", nullable=false)
}
, inverseJoinColumns={
@JoinColumn(name="volunteer_id", nullable=false)
}
)
private List<Volunteer> volunteers;
public Skill() {
}
public int getId() {
return this.id;
}
public void setId(int id) {
this.id = id;
}
public String getSkillDescription() {
return this.skillDescription;
}
public void setSkillDescription(String skillDescription) {
this.skillDescription = skillDescription;
}
public List<Volunteer> getVolunteers() {
return this.volunteers;
}
public void setVolunteers(List<Volunteer> volunteers) {
this.volunteers = volunteers;
}
}
@Entity
@Table(name="volunteer")
@NamedQueries({
@NamedQuery(name = "Volunteer.findAll", query = "SELECT v FROM Volunteer v"),
@NamedQuery(name = "Volunteer.findById", query = "SELECT v FROM Volunteer v WHERE v.id = :id"),
@NamedQuery(name = "Volunteer.findByPhone", query = "SELECT v FROM Volunteer v WHERE v.phone = :phone"),
@NamedQuery(name = "Volunteer.findByEmail", query = "SELECT v FROM Volunteer v WHERE v.email = :email"),
@NamedQuery(name = "Volunteer.findByFirstName", query = "SELECT v FROM Volunteer v WHERE v.firstName = :firstName"),
@NamedQuery(name = "Volunteer.findByLastName", query = "SELECT v FROM Volunteer v WHERE v.lastName = :lastName")})
public class Volunteer implements Serializable {
@Override
public String toString() {
return "Volunteer [id=" + id + ", email=" + email + ", firstName="
+ firstName + ", lastName=" + lastName + ", phone=" + phone
+ "]";
}
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(unique=true, nullable=false)
private int id;
@Column(length=255)
private String email;
@Column(name="first_name", length=255)
private String firstName;
@Column(name="last_name", length=255)
private String lastName;
@Column(length=255)
private String phone;
//bi-directional many-to-many association to Event
@ManyToMany(mappedBy="volunteers")
private List<Event> events;
//bi-directional many-to-many association to Skill
@ManyToMany(mappedBy="volunteers", cascade=CascadeType.ALL, fetch=FetchType.EAGER)
private List<Skill> skills;
public Volunteer() {
}
public int getId() {
return this.id;
}
public void setId(int id) {
this.id = id;
}
public String getEmail() {
return this.email;
}
public void setEmail(String email) {
this.email = email;
}
public String getFirstName() {
return this.firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return this.lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getPhone() {
return this.phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
public List<Event> getEvents() {
return this.events;
}
public void setEvents(List<Event> events) {
this.events = events;
}
public List<Skill> getSkills() {
return this.skills;
}
public void setSkills(List<Skill> skills) {
this.skills = skills;
}
}
@实体
@表(name=“志愿者”)
@命名查询({
@NamedQuery(name=“志愿者.findAll”,query=“从志愿者v中选择v”),
@NamedQuery(name=“志愿者.findById”,query=“从志愿者v中选择v,其中v.id=:id”),
@NamedQuery(name=“志愿者.findByPhone”,query=“从志愿者v中选择v,其中v.phone=:phone”),
@NamedQuery(name=“志愿者.findByEmail”,query=“从志愿者v中选择v,其中v.email=:email”),
@NamedQuery(name=“志愿者.findByFirstName”,query=“从志愿者v中选择v,其中v.firstName=:firstName”),
@NamedQuery(name=“志愿者.findByLastName”,query=“从志愿者v中选择v,其中v.lastName=:lastName”)}
公共类实现了可序列化{
@凌驾
公共字符串toString(){
return“志愿者[id=“+id+”,email=“+email+”,firstName=”
+firstName+”,lastName=“+lastName+”,phone=“+phone”
+ "]";
}
私有静态最终长serialVersionUID=1L;
@身份证
@GeneratedValue(策略=GenerationType.IDENTITY)
@列(unique=true,nullable=false)
私有int-id;
@列(长度=255)
私人字符串电子邮件;
@列(name=“first_name”,长度=255)
私有字符串名;
@列(name=“last_name”,长度=255)
私有字符串lastName;
@列(长度=255)
私人电话;
//事件的双向多对多关联
@许多人(mappedBy=“志愿者”)
私人列表活动;
//技能的双向多对多关联
@ManyToMany(mappedBy=“志愿者”,cascade=CascadeType.ALL,fetch=FetchType.EAGER)
私人名单技能;
公共志愿者(){
}
公共int getId(){
返回此.id;
}
公共无效集合id(内部id){
this.id=id;
}
公共字符串getEmail(){
返回此电子邮件;
}
公用电子邮件(字符串电子邮件){
this.email=电子邮件;
}
公共字符串getFirstName(){
返回这个.firstName;
}
public void setFirstName(字符串firstName){
this.firstName=firstName;
}
公共字符串getLastName(){
返回this.lastName;
}
public void setLastName(字符串lastName){
this.lastName=lastName;
}
公共字符串getPhone(){
还这个电话;
}
公用无效设置电话(字符串电话){
this.phone=电话;
}
公共列表getEvents(){
返回此项。事件;
}
公共void setEvents(列出事件){
这个事件=事件;
}
公共列表getSkills(){
归还这本书。技能;
}
公共技能(列出技能){
这就是:技能=技能;
}
}
列表为空,因此抓取似乎不起作用
获取一个空列表并不意味着“获取”不起作用,无论您使用的是惰性获取类型还是渴望获取类型,您都应该获取给定志愿者的技能记录(如果有的话)
因为映射看起来是正确的,所以我将首先查看生成的SQL并对数据库运行它以确认
persistence.xml
中设置以下属性:
<property name="eclipselink.logging.level" value="FINEST" />
<property name="eclipselink.logging.level.sql" value="FINEST" />
然后找到findById
和getSkills
的SQL查询,并对数据库运行它们
并且请用获得的给定id的结果更新问题(生成的SQL和数据是否正常的确认)。只需尝试使用em.flush(),它对我有用
Query q = em.createNamedQuery("Volunteer.findById").setParameter("id", id);
vo = (Volunteer) q.getSingleResult();
em.flush();
for(Skill s: vo.getSkills()){
System.out.println(s);
}
双向关系最常见的问题是当用户不同时维护双方时——JPA实体是普通java对象,JPA不会像EJB2.0那样为您修复关系。将志愿者添加到技能时,还必须将该技能添加到志愿者,以便缓存与您在数据库中强制执行的更改保持同步