与排序的多对多关系

Question

我正在尝试通过连接表中的附加属性在两个实体之间实现 MANY_TO_MANY 关系。 我找到了以下答案： how-to-do-a-many-to-many-relationship-in-spring-roo-with-attributes-within-de-relationship 但我未能尝试使提供的解决方案适应我的场景：

目前我有一个直接的 MANY_TO_MANY 关系：

 # book:
 entity jpa --class ~.domain.Book --testAutomatically
 field string --fieldName title --notNull
 field string --fieldName subtitle --notNull
 field string --fieldName description
 # n:m relationship to author
 field list --fieldName authors --type ~.domain.Author --cardinality MANY_TO_MANY

 # author:
 entity jpa --class ~.domain.Author --testAutomatically
 field string --fieldName firstName --notNull
 field string --fieldName lastName --notNull

按预期工作，但我需要让作者订购。我想通过定义关系表并向其中添加一个像“序列”这样的整数字段来实现这一点，但是当我尝试在 Book 中定义多对多关系时遇到了困难：

 entity jpa --class ~.domain.BookAuthorOrdered  --table book_author_ordered
 # the additional field to store sequence of authors:
 field number --fieldName authorSequence --type java.lang.Integer --notNull
 # reference to book:
 field reference --fieldName bookId --type ~.domain.Book --cardinality MANY_TO_ONE 

 # reference to author:
 field reference --fieldName authorId --type ~.domain.Author --cardinality MANY_TO_ONE

谁能给我一个提示，如何在 Book 中定义属性，以便我使用上面定义的连接表获得排序作者的列表？这是我尝试过的：

 # complete the relationship
 focus --class ~.domain.Book
 field list --type ~.domain.BookAuthorOrdered --fieldName orderedAuthors --cardinality ONE_TO_MANY --mappedBy bookId

Answer 1

尝试将@OrderBy 注释添加到实体字段（在.java 文件中）。举例：

   @ManyToMany
   @OrderBy("lastName ASC, firstName ASC")
   private List<Author> authors;

Answer 2

我为我的问题找到了一个或多或少可行的解决方案，但它仍然有一些缺点。它主要来自上述答案： How to do a many-to-many relationship in spring Roo, with attributes within de relationship?

使用表 book 和 author 的 id 作为组合主键手动创建连接表： roo> entity jpa --class ~.domain.BookAuthorOrdered --table book_author_ordered --identifierType ~.domain.BookAuthorOrderedId 字段编号 --fieldName authorSequence --type java.lang.Integer --notNull

然后编辑生成的id类BookAuthorOrderedId并添加组合主键：

@RooToString
@RooEquals
@RooIdentifier
public final class BookAuthorOrderedId {
   @ManyToOne
    @JoinColumn(name="book_id", insertable = false, updatable = false)
    private Book book;

   @ManyToOne
    @JoinColumn(name="author_id", insertable = false, updatable = false)
    private Author author;
}

现在是我感觉不好的部分，因为这对我来说似乎是一种解决方法。在书籍实体中，我为作者推送了 getter 方法并将其替换为连接表的查询：

   public List<Author> getAuthors()
    {

        // return Author.findAllAuthorsOfBook(this);


        System.out.println("getAuthors()");
        EntityManager em = new Book().entityManager;
        TypedQuery<Author> q = em.createQuery("SELECT o FROM Author AS o WHERE o.id IN ( SELECT OA.id.author FROM eu.books2ebooks.roomanova.domain.BookAuthorOrdered OA where OA.id.book = :book ) ", Author.class);
        q.setParameter("book", this);
        List<Author> authorList = q.getResultList(); 
        //this.setAuthors(authorList);
        return authorList;
    }

以及一种为新添加的作者直接获取 bean 值的方法：

public List<Author> getAddedAuthors() {
    return this.authors;
}

然后我不得不操纵 book 控制器来调用一个自写的方法来插入/更新连接表（在 create/update/..）：

public static void setOrderedBookAuthors(Book book, List<Author> authors) {
    // delete all associated authors of book:
    List<BookAuthorOrdered> bookAuthorOrdereds = BookAuthorOrdered.findAllBookAuthorOrdersOfBook(book);
    for (BookAuthorOrdered bookAuthorOrdered : bookAuthorOrdereds) {
        log.info("removing book author: " + printAuthor(bookAuthorOrdered.getId().getAuthor()));
        bookAuthorOrdered.remove();
    }
    if ( authors == null )
    {
        log.info("ordered authors: null. nothing to insert.");
        return;
    }
    log.info("inserting sorted authors: ");
    Integer authorSequence = 1;
    for (Author author : authors) {
        log.info("inserting book author sorted: " + printAuthor(author) + " as no " + authorSequence);
        BookAuthorOrdered bookAuthorOrdered = new BookAuthorOrdered();
        bookAuthorOrdered.setAuthorSequence(authorSequence);
        BookAuthorOrderedId id = new BookAuthorOrderedId(book, author);
        bookAuthorOrdered.setId(id);
        log.info("book author ordered: " + bookAuthorOrdered);
        bookAuthorOrdered.persist();

        authorSequence++;
    }
}

到目前为止，这是可行的，但感觉必须有一种更优雅的方式......