Jpa：存儲由實體組成的Value對象的集合

Question

@Entity 
class Question{ 
    @Id 
    private int id; 
    private String questionText; 

    @OneToMany 
    Set<AnswerOption> answerOptions; 
} 

class AnswerOption{ 
    private String option; 

    @ManyToOne 
    private Question question; 
} 

table-columns: 
Question: id, text 
AnswerOption: question_id, option 

example: 
Question: Which county are you from? 
Possible answers: Kent, Essex, Middlesex, Others 


Intended api usage: 
Question q = new Question("Which county are you from?"); 
q.addAnswerOption(new AnswerOption("Kent")) 
q.addAnswerOption(new AnswerOption("Essex")) 
q.addAnswerOption(new AnswerOption("Middlesex")) 
q.addAnswerOption(new AnswerOption("Others")) 
questionDao.save(q); 

我不需要AnswerOption的標識符，因爲我認爲AnswerOption是一個Value對象。有人可以推薦如何使用JPA來堅持這個模型，因爲我不確定用於AnswerOption類的註釋嗎？

謝謝。

Answer 1

我會說，使你的AnswerOption類也作爲實體。

@Entity 
class AnswerOption{ 
    private String option; 

    @ManyToOne 
    private Question question; 
} 

變化oneToMany映射Question類使用CASCADE選項如下：

@Entity 
class Question{ 

    @Id 
    private int id; 
    private String questionText; 

    @OneToMany(cascade = CascadeType.ALL, mappedBy="question") 
    Set<AnswerOption> answerOptions; 
} 

一旦這樣做，你的問題對象保存如下：

//get your hibernate session 
Session session = .... 
Question q = new Question("Which county are you from?"); 
q.addAnswerOption(new AnswerOption("Kent")) 
q.addAnswerOption(new AnswerOption("Essex")) 
q.addAnswerOption(new AnswerOption("Middlesex")) 
q.addAnswerOption(new AnswerOption("Others")) 

//use session to save the Question with AnswerOptionss 
session.save(q); 

確保您addAnswerOption方法Question如下：

public void addAnswerOption(AnswerOption answerOption){ 
    //setting the question as parent in answerOption 
    answerOption.setQuestion(this). 
    this.answerOptions.add(answerOption); 
}