JPA2.0：删除OneToMany RelationShip中的实体

@Entity
@NamedQueries({
   @NamedQuery(name="User.findByUserNamePassword",query="select c from User c where c.userName = :userName AND c.password = :password")
})
@Table(name=""USER"")
public class User implements Serializable {
    @OneToMany(mappedBy="user",cascade=CascadeType.ALL,orphanRemove=true)
    private List<Profession> professions;

    public List<Profession> getProfessions() {
       return professions;
    }

    public void setProfessions(List<Profession> professions) {
       this.professions = professions;
    }

    public void addProfession(Profession profession){
       if(this.professions == null){
          this.professions = new ArrayList<Profession>();
       }
       this.professions.add(profession);
       profession.setUser(this);
    }

    public void removeProfession(Profession profession){
       if(this.professions != null){
          professions.remove(profession);
          profession.setUser(null);
       }
    }
}

内部职业实体

@Entity
public class Profession implements Serializable {
    @ManyToOne
    @JoinColumn(name="UserId",nullable=false)
    private User user;

    public User getUser() {
       return user;
    }

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

然后在我的EJB里面我有这个

@Stateless
@LocalBean
@TransactionAttribute(TransactionAttributeType.REQUIRED)
public class ScholarEJB{

    /**
     * Add a profession to a target user
     * @param user
     * @param profession
     */
    public void addProfession(User user,Profession profession){
        //Put the user in a managed state. It is important to do this before
        //adding a new profession onto user
        user = find(User.class,user.getId());
        user.addProfession(profession);
        this.create(user);   //This is persist action
    }

    public void removeProfession(User user,user.getId());
        user.remove(user);
        this.update(user);  //merge action
        //this.create(user) //also try this as well,but it does not work
    }
}

现在addProfession工作得很漂亮,但removeProfession不起作用.不知道为什么？请帮忙.我需要驱逐缓存吗？