JPA with "Detached Entity passed to persist:"

Question

Hello, I have a problem because I use an intermediate table to save the Ids of other 2 tables. Except that the way that Mapeei, I can’t save in this table because apparently JPA understands that I can’t pass the null entity nor pass the filled object to q it does a "MERGE" without change, follows:

instance.setDtCriacao(new Date(System.currentTimeMillis()));
instance.setQtMidiaTransmissao(dualListMidias.getTarget().size());
instance = playlistBean.salvarPlaylist(referenceValue);

int i = 1;
for(Midia midias : dualListMidias.getTarget()){             
    MidiaPlaylist midiaPlaylist = new MidiaPlaylist();
    MidiaPlaylistPK midiaPlaylistPK = new MidiaPlaylistPK();
    midiaPlaylistPK.setIdMidia(midias.getIdMidia());
    midiaPlaylistPK.setIdPlaylist(instance.getIdPlaylist());                
    midiaPlaylist.setPk(midiaPlaylistPK);               
    midiaPlaylist.setNrOrdem(i++);
    midiaPlaylist.setMidia(midias); 
    midiaPlaylist.setPlaylist(instance);

    //playlistBean.salvar(midiaPlaylist);
    midiaPlaylistBean.salvar(midiaPlaylist);
}   

Saved in "playlist" table so you have the ID I want and the media Ids are already in the list dualListMidias.getTarget(), then I do a for to record all id.playlist and id.midia in the media table

My Midiaplaylistbean

@TransactionAttribute(TransactionAttributeType.REQUIRED)
public MidiaPlaylist salvar(MidiaPlaylist entity){
    try{
        entity = super.save(entity);
    }catch(Exception e){
        e.printStackTrace();
    }
    return entity;
}

My Midiaplaylist

@EmbeddedId 
private MidiaPlaylistPK pk = new MidiaPlaylistPK();

public MidiaPlaylist(){
}

@MapsId("idMidia")
@ManyToOne
@JoinColumn(name="id_midia", referencedColumnName="id_midia")
private Midia midia;

@MapsId("idPlaylist")
@ManyToOne
@JoinColumn(name="id_playlist", referencedColumnName="id_playlist")
private Playlist playlist;  

@Column(name="nr_ordem", nullable=false)
private int nrOrdem;


public Midia getMidia() {
    return midia;
}

public void setMidia(Midia midia) {
    this.midia = midia;
}

public Playlist getPlaylist() {
    return playlist;
}

public void setPlaylist(Playlist playlist) {
    this.playlist = playlist;
}

public void setPk(MidiaPlaylistPK id) {
    this.pk = id;
}

public MidiaPlaylistPK getPk() {
    return this.pk;
}

public void setNrOrdem(int nrOrdem){
    this.nrOrdem = nrOrdem;
}

public int getNrOrdem(){
    return this.nrOrdem;
}

Playlist.java

@Id
@GeneratedValue
@Column(name="id_playlist")
private Long idPlaylist;

@OneToMany(mappedBy = "playlist", fetch=FetchType.LAZY)
private List<MidiaPlaylist> midiaPlaylist;

public List<MidiaPlaylist> getMidiaPlaylist(){
    return midiaPlaylist;
}

public void setMidiaPlaylist(List<MidiaPlaylist> midiaPlaylist){
    this.midiaPlaylist = midiaPlaylist;
}

public Playlist() {
}   

public Long getIdPlaylist() {
    return this.idPlaylist;
}

public void setIdPlaylist(Long idPlaylist) {
    this.idPlaylist = idPlaylist;
}

The mistake is:

Detached Entity passed to persist: com.bcm.midia.database.Entity.Midia

Where I think the mistake is: in the mapping of Midia

@Id
@GeneratedValue
@Column(name="id_midia")
private Long idMidia; 

@OneToMany(mappedBy = "midia", fetch = FetchType.LAZY, cascade=CascadeType.MERGE)   
private List<MidiaPlaylist> midiaPlaylist;

Could someone explain to me why I can’t just save in the Midiaplaylist table this way of mapping Many-to-Many?