JPA框架會自動保存一對多關系嗎？

假設我有一對多的關系：

import javax.persistence.*;
import java.io.Serializable;
import java.util.Set;

@Entity
@Table(name = "books")
public class Book implements Serializable {

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

    private String title;
    private String author;
    @Column(unique = true)
    private String isbn;

    @OneToMany(mappedBy = "book", fetch = FetchType.LAZY,
            cascade = CascadeType.ALL)
    private Set<Page> pages;

    public Book() {
    }

    public Book(String title, String author, String isbn) {
        this.title = title;
        this.author = author;
        this.isbn = isbn;
    }

    // getters and setters, equals(), toString() .... (omitted for brevity)
}

和

import javax.persistence.*;
import java.io.Serializable;

@Entity
@Table(name = "pages")
public class Page implements Serializable {

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

    private int number;
    private String content;
    private String chapter;

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "book_id", nullable = false)
    private Book book;

    public Page() {
    }

    public Page(int number, String content, String chapter, Book book) {
        this.number = number;
        this.content = content;
        this.chapter = chapter;
        this.book = book;
    }

    // getters and setters, equals(), toString() .... (omitted for brevity)
}

并將其存盤在：

// create a new book
Book book = new Book("Java 101", "John Doe", "123456");
    
// save the book
bookRepository.save(book);
    
// create and save new pages
pageRepository.save(new Page(1, "Introduction contents", "Introduction", book));
pageRepository.save(new Page(65, "Java 8 contents", "Java 8", book));
pageRepository.save(new Page(95, "Concurrency contents", "Concurrency", book));

問題是：我真的需要save手動訪問每個頁面嗎？我可以只使用 java 集合，然后只保存主要物體，如：

book.pages.add(new Page(1, "Introduction contents", "Introduction", book));

book.pages.add(new Page(65, "Java 8 contents", "Java 8", book));

book.pages.add(new Page(95, "Concurrency contents", "Concurrency", book));

bookRepository.save(book);

該示例取自https://attacomsian.com/blog/spring-data-jpa-one-to-many-mapping

而且我想知道存盤關系的正確和最佳方式，這就是為什么我在這里問而不只是自己進行實驗，因為這篇文章似乎誤導了很多人

uj5u.com熱心網友回復：

下面是cascade在Book#pages發揮作用。正如您將其配置為那樣CascadeType.ALL，這意味著當您使用EntityManagerto persist()on a 時Book，它將自動呼叫persist()其所有Page.

使用cascadeis disable ，您必須呼叫以下命令來保存新 Book 及其所有頁面：

entityManager.persist(book);
entityManager.persist(page1);
entityManager.persist(page2);
....
entityManager.persist(pageN);

但是在啟用級聯的情況下，您只需要呼叫以下內容，因為persist()頁面上的所有內容都將被級聯以自動呼叫。

entityManager.persist(book);

由于 spring-data-jpa 存盤庫內部僅使用相同的EntityManager方式保存同一事務的物件，因此如果啟用級聯，您只需要呼叫以下代碼即可保存書籍及其頁面：

Book book = new Book("Java 101", "John Doe", "123456");
book.pages.add(new Page(1, "Introduction contents", "Introduction", book));
book.pages.add(new Page(65, "Java 8 contents", "Java 8", book));
book.pages.add(new Page(95, "Concurrency contents", "Concurrency", book));
bookRepository.save(book);

否則，如果級聯被禁用，您必須呼叫以下代碼來保存 Book 及其頁面：

Book book = new Book("Java 101", "John Doe", "123456");
bookRepository.save(book);

pageRepository.save(new Page(1, "Introduction contents", "Introduction", book));
pageRepository.save(new Page(65, "Java 8 contents", "Java 8", book));
pageRepository.save(new Page(95, "Concurrency contents", "Concurrency", book));

標籤：爪哇 休眠 科特林 jpa 弹簧数据-jpa

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