JPA 休眠 4 延迟加载问题。如何在不急切的情况下在 ManyToOne 中加载惰性数据

Question

有 2 个 table。

一个 table 与另一个 table 有很多联系。

所有连接都是延迟加载风格。当我想从 UppeningUsers 那里得到一些东西时，延迟加载起作用了，我可以获取数据。这部分说清楚了。

Session session = this.sessionFactory.getCurrentSession();
    List<UppeningUsers> countryList =  session.createQuery("from UppeningUsers").list();

如果我调用 listPhotoObj、peopleWhoBlockedMe、peopleIBlocked，这会简单地获取代理，然后它们会被初始化。所以我明白了这部分。

但是如果我调用

      Session session = this.sessionFactory.getCurrentSession();
List<UsersPhotos> countryList =  session.createQuery("from UsersPhotos").list();

然后

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "user_id")
private UppeningUsers user;

这家伙是代理人，这意味着我无法获得任何数据。即使我请求 get 我也没有得到任何信息。 Table 1

Table 2

所以如果我从妈妈那里打电话table。我们可以在需要时获得列表。这部分没问题。

现在的问题是，如果我从 child table 那里调用 manytoOne relation.I 从那里获取代理。我没有得到完整的信息。如果我渴望，我会得到它，但我不想要那样。有没有其他方法可以让我在需要时无需执行 EAGER 即可获得这些惰性数据。

更新 1

    package com.uppening.models;

    import com.sun.istack.internal.Nullable;
    import org.hibernate.annotations.Formula;
    import org.hibernate.annotations.Proxy;

    import javax.persistence.*;
    import java.util.Set;


   @Entity
  @Table(name = "uppening_users")
  @Proxy(lazy = true)

   public class UppeningUsers {

@Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.IDENTITY)
int id;

private String name;
private boolean isblocked;

private String mail;
private String birthday;
private String source;
private String gender;
private String link;

private String description;
private String traveller;
private String interests;
private String device;
private String location;
private String showup;

@OneToMany(mappedBy = "user", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<UsersPhotos> listPhotoObj;

@OneToMany(mappedBy = "personBlocked", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<UserBlocks> peopleWhoBlockedMe;

@OneToMany(mappedBy = "blocker", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<UserBlocks> peopleIBlocked;

@OneToMany(mappedBy = "activityUser", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<UserActivities> listActivities;


@Formula(" DATE_FORMAT( FROM_DAYS( TO_DAYS( NOW( ) ) - TO_DAYS( birthday ) ) ,  '%Y' )    ")
@Nullable
private Integer age;














public UppeningUsers() {
    super();
}

@Transient
public Integer getAge() {
    return age;
}

public UppeningUsers(String name, boolean isblocked, String mail, String birthday,
                     String source, String gender, String link, String description,
                     String traveller, String interests, String device, String location,
                     String showup, Set<UsersPhotos> listPhotoObj, Set<UserBlocks> peopleWhoBlockedMe,
                     Set<UserBlocks> peopleIBlocked, Set<UserActivities> listActivities, Integer age) {
    this.name = name;
    this.isblocked = isblocked;
    this.mail = mail;
    this.birthday = birthday;
    this.source = source;
    this.gender = gender;
    this.link = link;
    this.description = description;
    this.traveller = traveller;
    this.interests = interests;
    this.device = device;
    this.location = location;
    this.showup = showup;
    this.listPhotoObj = listPhotoObj;
    this.peopleWhoBlockedMe = peopleWhoBlockedMe;
    this.peopleIBlocked = peopleIBlocked;
    this.listActivities = listActivities;
    this.age = age;
}
public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public boolean isIsblocked() {
    return isblocked;
}

public void setIsblocked(boolean isblocked) {
    this.isblocked = isblocked;
}

public String getMail() {
    return mail;
}

public void setMail(String mail) {
    this.mail = mail;
}

public String getBirthday() {
    return birthday;
}

public void setBirthday(String birthday) {
    this.birthday = birthday;
}

public String getSource() {
    return source;
}

public void setSource(String source) {
    this.source = source;
}

public String getGender() {
    return gender;
}

public void setGender(String gender) {
    this.gender = gender;
}

public String getLink() {
    return link;
}

public void setLink(String link) {
    this.link = link;
}

public String getDescription() {
    return description;
}

public void setDescription(String description) {
    this.description = description;
}

public String getTraveller() {
    return traveller;
}

public void setTraveller(String traveller) {
    this.traveller = traveller;
}

public String getInterests() {
    return interests;
}

public void setInterests(String interests) {
    this.interests = interests;
}

public String getDevice() {
    return device;
}

public void setDevice(String device) {
    this.device = device;
}

public String getLocation() {
    return location;
}

public void setLocation(String location) {
    this.location = location;
}

public String getShowup() {
    return showup;
}

public void setShowup(String showup) {
    this.showup = showup;
}

public Set<UsersPhotos> getListPhotoObj() {
    return listPhotoObj;
}

public void setListPhotoObj(Set<UsersPhotos> listPhotoObj) {
    this.listPhotoObj = listPhotoObj;
}

public Set<UserBlocks> getPeopleWhoBlockedMe() {
    return peopleWhoBlockedMe;
}

public void setPeopleWhoBlockedMe(Set<UserBlocks> peopleWhoBlockedMe) {
    this.peopleWhoBlockedMe = peopleWhoBlockedMe;
}

public Set<UserBlocks> getPeopleIBlocked() {
    return peopleIBlocked;
}

public void setPeopleIBlocked(Set<UserBlocks> peopleIBlocked) {
    this.peopleIBlocked = peopleIBlocked;
}

public Set<UserActivities> getListActivities() {
    return listActivities;
}

public void setListActivities(Set<UserActivities> listActivities) {
    this.listActivities = listActivities;
}

public void setAge(Integer age) {
    this.age = age;
}
   }

用户照片Class

    package com.uppening.models;

    import org.hibernate.annotations.Proxy;

    import javax.persistence.*;

    @Entity
    @Table(name="uppening_resimler")
    @Proxy(lazy = true)

    public class UsersPhotos {

@Id
@Column(name="id")
@GeneratedValue(strategy= GenerationType.IDENTITY)
int id;

@Column(name="photo")
private
String photo;
public UsersPhotos() {
    super();
}

public UsersPhotos(String photo, UppeningUsers user) {
    this.photo = photo;
    this.user = user;
}

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "user_id")
private UppeningUsers user;

public String getPhoto() {
    return photo;
}

public void setPhoto(String photo) {
    this.photo = photo;
}

public UppeningUsers getUser() {
    return user;
}

public void setUser(UppeningUsers user) {
    this.user = user;
}

}

更新 2 我看到，如果我在此 UserPhoto object 中调用任何 setter 用户，它就会获取信息。例如 countryList .get(0).getUser().getLink() 实际上进入数据库并检索信息..但只有该信息不会作为完整的 object 数据响应，我的意思是 countryList .get(0) .getUser() 这个。我不想获取所有数据，所以这就是我的问题。

更新 3 获取 sql 建议是答案，但它产生了另一个问题

   @OneToMany(mappedBy = "user", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<UsersPhotos> listPhotoObj;

@OneToMany(mappedBy = "personBlocked", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<UserBlocks> peopleWhoBlockedMe;

@OneToMany(mappedBy = "blocker", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<UserBlocks> peopleIBlocked;

@OneToMany(mappedBy = "activityUser", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<UserActivities> listActivities;

这 4 个正在创建 SQL，即使它们是延迟加载。

假设我只想要

private String mail;
private String birthday;
private String source;
private String gender;
private String link;

那么我实际上并不需要那些 sql 发生。

Answer 1

您可以使用 Hibernate.initialize() 触发任何关联数据的提取，只需确保在同一个 session

中使用它

示例：

Session session = this.sessionFactory.getCurrentSession();
List<UsersPhotos> countryList =  session.createQuery("from UsersPhotos").list();

for(UsersPhotos usersPhotos : countryList){ // don't forget the null countryList case
  Hibernate.initialize(usersPhotos.getUser());
}

Answer 2

试试这个：

List<UsersPhotos> countryList =  session.createQuery("from UsersPhotos up JOIN FETCH up.user").list();

检查此以获取更多信息：Difference between JOIN and JOIN FETCH in Hibernate

更新 1： 您可以使用 LEFT JOIN FETCH instead of JOIN FETCH 这样查询就不会排除没有 UppeningUsers.

的 UsersPhotos

List<UsersPhotos> countryList =  session.createQuery("from UsersPhotos up LEFT JOIN FETCH up.user").list();

JPA 休眠 4 延迟加载问题。如何在不急切的情况下在 ManyToOne 中加载惰性数据

JPA hibernate 4 lazy load issue. How to load lazy data in ManyToOne without eager

java

hibernate

jpa

hibernate-4.x