@ManyToMany 链接表中没有条目

Question

也许这里有人可以给我一个提示，错误可能出现在哪里（JSF 2.2，Glassfish 4.0）：

• 我有两个具有多对多关系的实体（参见示例）
• 当我在 glassfish 中部署我的项目时，所有表（也是链接表）都会正确生成（在 persistence.xml 中启用创建表）：TAGUSERWISH、TAGUSERWISH_WISH（链接表）、WISH
• 当我执行持久化（参见示例）实体“wish”和“tagUserWish”时，会正确持久化，但是当我直接查看 mysql 表时，没有任何内容写入链接表。但是当我用 JPA 读出“wish”时，List<TagUserWish> 被填满了
• 新会话一开始（重新部署）List<TagUserWish> 在使用 JPA 读出时也是空的

所有者实体：

@Entity
public class Wish implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String subject;
    private String abstractT;

    @OneToOne
    private User user;

    @ManyToMany(mappedBy = "wishes", cascade = {CascadeType.ALL} )
    private List<TagUserWish> tags = new LinkedList<>();

    public void addTag(TagUserWish tag){
        tags.add(tag);
    }

    public void setTags(List<TagUserWish> tags) {
        this.tags = tags;
    }       

    public void removeTag(TagUserWish tag){
        tags.remove(tag);
    }

    public List<TagUserWish> getTags(){
        return tags;
    }

    public String getSubject() {
        return subject;
    }

    public void setSubject(String subject) {
        this.subject = subject;
    }

    public String getAbstractT() {
        return abstractT;
    }

    public void setAbstractT(String abstractT) {
        this.abstractT = abstractT;
    }

    public User getUser() {
        return user;
    }

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


    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (id != null ? id.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof Wish)) {
            return false;
        }
        Wish other = (Wish) object;
        if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "eu.citato.main.model.Wish[ id=" + id + " ]";
    }

}

实体 2：

@Entity
public class TagUserWish implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;        
    private String name;

    public TagUserWish() {
    }          

    public TagUserWish(String name) {
        this.name = name;
    }          

    @ManyToMany
    private List<Wish> wishes = new LinkedList<>();

    public void addWish(Wish wish){
        wishes.add(wish);
    }

    public void setWishes(List<Wish> wishes) {
        this.wishes = wishes;
    }       

    public void removeWish(Wish tag){
        wishes.remove(tag);
    }

    public List<Wish> getWishes(){
        return wishes;
    }

    public String getName() {
        return name;
    }

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

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }


    @Override
    public int hashCode() {
        int hash = 0;
        hash += (id != null ? id.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof TagUserWish)) {
            return false;
        }
        TagUserWish other = (TagUserWish) object;
        if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "eu.citato.main.model.Tag[ id=" + id + ", name="+name+" ]";
    }     
}

我如何坚持：

@javax.inject.Named 
@SessionScoped
public class WishPM implements Serializable {

    @EJB
    private WishService wls;

    public void commitEditWish(){        
        List<TagUserWish> selTags = new ArrayList<>();
        selTags.add(new TagUserWish("Tag1"));
        selTags.add(new TagUserWish("Tag2"));
        currentWish = new Wish();
        currentWish.setSubject("wishSubject");
        currentWish.setAbstractT("wishAbstract");
        currentWish.setTags(selTags);
        wls.createWish(currentWish);
    }
}

还有愿望服务：

@Stateless
public class WishService implements Serializable{

    @PersistenceContext(unitName = "WishlistPU")
    private EntityManager em;

    public void createWish(Wish entity){
        em.persist(entity);
    }
}

Answer 1

关系基于关系的所有者方而持续存在。双向关系的所有者是反面的mappedBy 值的所有者。在以下情况下，关系的所有者是 TagUserWish 实体中的 wishes 字段

@ManyToMany(mappedBy = "wishes", cascade = {CascadeType.ALL} )
private List<TagUserWish> tags = new LinkedList<>();

因为TagUserWish 的实例确实有空的wishes 集合，所以关系不会保持。问题可以通过在TagUserWish的实例中添加相关的Wish来解决，例如：

...
TagUserWish tuw1 = new TagUserWish("Tag1")
TagUserWish tuw2 = new TagUserWish("Tag2")

selTags.add(tuw1);
selTags.add(tuw2);

currentWish = new Wish();
tuw1.addWish(currentWish); //setting to owner side of relationship
tuw2.addWish(currentWish); //setting to owner side of relationship
...