JPA休眠4延遲加載問題。 如何不急切地在ManyToOne中加載懶數據

Question

有2張桌子。

一個表與另一個表有許多連接。

所有連接均為延遲加載樣式。 當我想從UppeningUsers獲得一些東西時，可以進行延遲加載，並且可以獲取數據。 這部分很清楚。

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

這只是去獲取listPhotoObj，peopleWhoBlockedMe，peopleIBlocked的代理（如果我調用它們，則它們將被初始化）。 所以我理解了這一部分。

但是如果我打電話

      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;

這個人是代理人，這意味着我無法獲取任何數據。 即使我要求得到我也沒有得到任何信息。 表格1

表2

因此，如果我從母表打來電話。 我們會在需要時獲得列表。 這部分還可以。

現在的問題是，如果我從有多對多關系的子表中調用。我從那里獲得代理。 我沒有得到足夠的信息。 如果我做得更好，我會得到的，但是我不要。 還有什么其他方法可以在我需要時不執行EAGER的情況下獲取此惰性數據。

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;
}
   }

UsersPhotos類

    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對象中調用User的任何setter，則它將獲取信息。 例如countryList .get（0）.getUser（）。getLink（）實際上進入數據庫並檢索信息。但是，只有該信息不能作為完整的對象數據響應，我的意思是countryList .get（0）.getUser（）這個。 我不想獲取所有數據，所以這就是我的問題。

UPDATE 3 Fetch sql建議是答案，但是它創建了另一個問題

   @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;

盡管它們是延遲加載的，但這四個仍在創建SQL。

假設我只想要

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

那么我實際上並不需要發生這些sql。

Answer 1

您可以使用Hibernate.initialize()觸發任何關聯數據的獲取，只需確保在同一session使用它即可

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

嘗試這個 ：

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

檢查更多信息： Hibernate中JOIN和JOIN FETCH之間的區別

更新1：您可以使用LEFT JOIN FETCH ，而不是連接抓取 ，因此查詢將不排除UsersPhotos不具有UppeningUsers 。

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