带Hibernate的JPA-合并性能问题

我偶然发现

EntityManager

的

merge

方法存在问题

我有这门课

@Entity
public class QuestionList {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String name;

    @ManyToOne
    private UserEntity user;

    @OneToMany(cascade = CascadeType.ALL)
    private List<QuestionUnit> units = new ArrayList<QuestionUnit>();

    public List<QuestionUnit> getUnits() {
        return units;
    }

    public void setUnits(List<QuestionUnit> units) {
        this.units = units;
    }

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void addQuestionUnit(QuestionUnit QuestionUnit) {
        this.units.add(QuestionUnit);
    }

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

    public UserEntity getUser() {
        return this.user;
    }

}

例如，在这个层次结构中有3个具体的类

@Question("openQuestion")
@Entity
public class OpenQuestion extends QuestionUnit {

    public void setQuestionContent(String questionContent) {
        this.questionContent = questionContent;
    }

    private String questionContent;

    public OpenQuestion() {
        this(null, new OpenQuestionAnswer());
    }

    public OpenQuestion(String questionContent, AnswerUnit correctAnswer) {
        super(correctAnswer);
        this.questionContent = questionContent;
    }

    public String getQuestionContent() {
        return this.questionContent;
    }

    public String getTitle() {
        return questionContent;
    }
}

@Transactional(propagation = Propagation.REQUIRED)
public void update(QuestionList questionList) {
    entityManager.merge(questionList);
}

---

此方法用于所有更新，因为列表处于分离状态。

它认为问题是由于使用列表而不是Set造成的

@OneToMany(cascade = CascadeType.ALL)
private List<QuestionUnit> units = new ArrayList<QuestionUnit>();

@OneToMany（cascade=CascadeType.ALL）
私有列表单位=新的ArrayList（）；

改为

@OneToMany(cascade = CascadeType.ALL)
private Set<QuestionUnit> units = new HashSet<QuestionUnit>();

@OneToMany（cascade=CascadeType.ALL）
私有集合单位=新HashSet（）；

---

是否可以包含QuestionUnit类和执行删除/添加对象、合并的代码？

@OneToMany(cascade = CascadeType.ALL)
private Set<QuestionUnit> units = new HashSet<QuestionUnit>();