未生成 JPA @ManyToOne 外键？

Question

我的应用程序中有两个由列表表示的多对一关系。对于“ChapterSection - ManyToOne - Chapter”关系，在持久化实体时将外键插入表中（在表“ChapterSection”中存储“Chapter”的外键）。对于其他关系，即“Chapter” - 多对一 - 文档”。

我使用 ddl.generation “drop-and-create-tables”。在数据库中，我可以看到，“Chapter.fk_document_iddocument”列被标记为引用文档 ID 的索引外键。 （我使用 EclipseLink 和 MySQL）。

我看不出这两种关系之间的区别，以及为什么一种有效而另一种无效。

文档实体：

@Entity
public class Document implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="iddocument")
    private Long id;

    @Column(name="document_name")
    private String documentName;

    @OneToMany(mappedBy="Document", cascade = CascadeType.PERSIST)
    private List<Chapter> chapters;

    @Enumerated(EnumType.STRING)
    @Column(name="document_type")
    private DocumentTypes documentType;

//...getters, setters and other generated methods

章节实体：

@Entity
public class Chapter implements Serializable {

    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="idchapter")
    private Long id;

    @Column(name="chapter_order")
    private int chapterOrder;

    @Column(name="parent_chapter")
    private Long parentChapter;

    @Column(name="chapter_name")
    private String chapterName;

    @ManyToOne(optional=false)
    @JoinColumn(name="fk_document_iddocument")
    private Document document;

    @OneToMany(mappedBy="Chapter", cascade=CascadeType.PERSIST)
    List<ChapterSection> chapterSections;

//...getters, setters and other generated methods

章节实体：

@Entity
public class ChapterSection implements Serializable {

    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="idchaptersection")
    private Long idChapterSection;

    @Column(name="section_name")
    private String sectionName;

    @Column(name="section_order")
    private int sectionOrder;

    @Column(name="content")
    private String content;

    @ManyToOne
    @JoinColumn(name="fk_chapter_idchapter")
    private Chapter chapter;

 //...getters, setters and other generated methods

我创建文档的方法：

public void createDocument() {

       List <Chapter> chapters = new ArrayList<>();

            for (int i = 0; i <= 4; i++) {
                Chapter chapter = new Chapter();
                chapter.setChapterOrder(i);
                chapter.setChapterName("Chapter "+i);
                List <ChapterSection> chapterSections = new ArrayList<>();
                for (int j = 0; j <= 4; j++) {
                    ChapterSection chapterSection = new ChapterSection();
                    chapterSection.setChapter(chapter);
                    chapterSection.setSectionName("Chapter "+i+" Section");
                    chapterSection.setSectionOrder(j);
                    chapterSection.setContent("Kapitel "+i+ ", Section "+j+" Content!");
                    chapterSections.add(chapterSection);
                }
                chapter.setChapterSections(chapterSections);
                chapters.add(chapter);
            }


        document.setDocumentName("My Doc");
        document.setChapters(chapters);
        document.setDocumentType("My Doc Type");
        documentDAO.persistDocument(document);
}

Answer 1

• @OneToMany 注释的mappedBy 元素在 JPA 规范中定义如下：

拥有关系的字段或属性。除非关系是单向的，否则是必需的。

根据此定义，您的mappedBy 元素必须设置为（值应该是字段名而不是类名）：

@OneToMany(mappedBy="document", cascade = CascadeType.PERSIST)
private List<Chapter> chapters;

@OneToMany(mappedBy="chapter", cascade=CascadeType.PERSIST)
List<ChapterSection> chapterSections;

• 在您的createDocument() 方法中，您尚未创建Document 和Chapter 之间的关系。所以你应该把它们绑起来如下：

  chapter.setDocument(document);