@Entity
@Table(uniqueConstraints=
   {@UniqueConstraint(columnNames={"name"})})
public class PlayList {
   private Long id;
   private String name;
   private List<Song> songs;
   
   ...
   
   public void setId(Long id) {
      this.id = id;
   }
   @Id
   @GeneratedValue
   public Long getId() {
      return id;
   }
   
   public void setSongs(List<Song> songs) {
      this.songs = songs;
   }
   
        @OneToMany(cascade={CascadeType.PERSIST,CascadeType.MERGE})   
   public List<Song> getSongs() {
      return songs;
   }

}


@Entity
@Table(uniqueConstraints=
{@UniqueConstraint(columnNames={"name"})})
public class Song {
   private Long id;
   private String name;
   ...
   public void setId(Long id) {
      this.id = id;
   }
   @Id
   @GeneratedValue
   public Long getId() {
      return id;
   }
}

create table PlayList (id bigint not null auto_increment, name varchar(255), primary key (id), unique (name))
create table PlayList_Song (PlayList_id bigint not null, songs_id bigint not null, unique (songs_id))
create table Song (id bigint not null auto_increment, name varchar(255), primary key (id), unique (name))

entityManager.remove( aSong );


Caused by: java.sql.BatchUpdateException: Cannot delete or update a parent row: a foreign key constraint fails ('music/playlist_song`, CONSTRAINT `FK1428A70D9548933E` FOREIGN KEY (`songs_id`) REFERENCES `song` (`id`))
   at com.mysql.jdbc.ServerPreparedStatement.executeBatch(ServerPreparedStatement.java:647)
   at org.jboss.resource.adapter.jdbc.WrappedStatement.executeBatch(WrappedStatement.java:517)
   at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:58)
   at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:195)
   ... 57 more

Song pSong = entityManager.find(Song.class,songId);
           
List<PlayList> playlists = entityManager.createQuery("SELECT p FROM PlayList AS p").getResultList();
                       
for( PlayList p : playlists ) {               
      p.getSongs().remove(pSong);
}
entityManager.flush();
           
entityManager.remove(pSong);