实体类

// 标签类

@Entity

public class Label {

@Id

@Column(name = "lid",unique = true,nullable = false)

@GeneratedValue(strategy = GenerationType.AUTO)

private Integer lid;

private String tag;

@ManyToMany(fetch = FetchType.EAGER)

@Cascade(value = {CascadeType.ALL}) // 设置级联关系

@JoinTable(name = "song_label",// 指定第三张表

joinColumns = {@JoinColumn(name = "label_id")},//本表与中间表的外键对应

inverseJoinColumns = {@JoinColumn(name = "song_id")}

)

private Set<Song> songs = new HashSet<>();

// setter and getter

｝

// 歌曲类

@Entity

public class Song {

@Id

@Column(name = "sid",unique = true,nullable = false)

@GeneratedValue(strategy = GenerationType.AUTO)

private Integer sid;

private String title;

private String special;

@ManyToMany(fetch = FetchType.EAGER)

@Cascade(value = { CascadeType.ALL})

@JoinTable(

name = "song_label",

joinColumns = {@JoinColumn(name = "song_id")},//本表与中间表的外键对应

inverseJoinColumns = {@JoinColumn(name = "label_id")}

)

private Set<Label> labels = new HashSet<>();

// setter and getter

｝

关联关系: 一首歌曲可以对应多个标签,一个标签可以对应多首歌曲

遇到的级联保存问题： 在添加已经存在的标签记录时保错org.hibernate.PersistentObjectException: detached entity passed to persist

测试代码

@Test

public void test1() {

Song song = new Song();

song.setSpecial("等你下课");

song.setTitle("等你下课");

Label label1 = new Label();

label1.setTag("华语");

Label label2 = new Label();

label2.setTag("内地");

song.getLabels().add(label1);

song.getLabels().add(label2);

this.songDao.save(song);//因设置级联关系CascadeType.ALL相应会在Label表添加记录

}

@Test

public void test123(){

Song song = new Song();

song.setSpecial("流星花园");

song.setTitle("北极星的眼泪");

Label label1 = this.labelDao.findByTag("爱情");

Label label2 = this.labelDao.findByTag("华语");

if (label2 == null){

label2 = new Label();

label2.setTag("华语");

}

if(label1 == null){

label1 = new Label();

label1.setTag("爱情");

}

song.getLabels().add(label1);

song.getLabels().add(label2);

this.songDao.save(song);// 报错org.hibernate.PersistentObjectException: detached entity passed to persist: com.example.data.bean.Label

}

test1()能够添加成功，到了test2时由于Label表存在”华语”这条记录，保存会出错

疑问：如何在Label表存在记录时执行更新而不是保存？

在此先感谢大神路过指点迷津哈哈