我偶然发现merge
方法的问题EntityManager
。JPA与休眠 - 合并性能问题
我有这个类
@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;
}
}
现在,如果我只是修改的对象之一units
合并是好的,但如果我删除或添加新对象的集合,该合并的方式发生的事情是我得到delete from QuestionList_QuestionUnit where QuestionList_id=?
,然后逐行添加每一行insert into QuestionList_QuestionUnit (QuestionList_id, units_id) values (?, ?)
我想知道,是否有可能告诉JPA/Hibernate只添加/删除与添加/删除的对象关联的行?或者,它是合并的方式只与集合工作,在我的情况下,我需要编写我自己的查询来更新数据库。
我在问,因为这个集合可能会非常庞大,只是删除所有行并重新插入几乎所有行,似乎不是一个更新表的好方法。
编辑:根据要求:
@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class QuestionUnit {
@Id
@GeneratedValue(strategy = GenerationType.TABLE)
private long id;
@OneToOne(cascade = CascadeType.ALL)
private AnswerUnit correctAnswer;
public QuestionUnit(AnswerUnit correctAnswer) {
this.correctAnswer = correctAnswer;
}
public void setCorrectAnswer(AnswerUnit correctAnswer) {
this.correctAnswer = correctAnswer;
}
public AnswerUnit getCorrectAnswer() {
return this.correctAnswer;
}
public long getId() {
return id;
}
public void setId(long id){
this.id=id;
}
public abstract Object getQuestionContent();
public abstract String getTitle();
}
有这层3中的具体类,例如
@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);
}
这种方法适用于所有的更新,因为列表是处于分离状态。
您可以包括QuestionUnit类和被做删除/添加对象的代码,合并吗? – gkamal
发布代码片段。 – Andna