MySql-一对多连接，将使用JDBI的连接映射到列表

Question

我试图用JDBI编写一个对象查询，它将从左表中抓取一个完整的行，并将右表中所有匹配的行作为List（一个作者可以有很多本书）连接起来。

作者id、姓名、创建日期、更新日期、电子邮件、电话号码

图书编号、标题、作者、类别、创建日期、更新日期

我要创建的最终对象的结构如下所示：

class AuthorWithBooks() {
  int id,
  String name,
  List<String> categories,
  long createdAt,
  long updatedAt,
  String email,
  String phoneNumber
  List<Book> books
}

书在哪里：

class Book {
  id,
  title,
  authorId,
  categories,
  createdAt,
  updatedAt
}

这是我正在尝试的查询（不按原样抓取图书列表）

@SqlQuery("SELECT " + AUTHOR_COLUMN MAMES + ", " + BOOK_COLUMN_NAMES + " FROM authors as author" +
      " LEFT JOIN books AS book" +
      " ON author.id = book.authorId" +
      " WHERE id = :authorId")
  List<AuthorWithBooks> getAuthorWithBooks(@Bind("authorId") int authorId);

如果有人能为我指出正确的方向，我将不胜感激！

谢谢

Answer 1

看起来你需要@UseRowReducer

您的示例的实现如下所示：

@SqlQuery("SELECT a." + AUTHOR_COLUMN MAMES + ", b." + BOOK_COLUMN_NAMES + " FROM authors as author" +
  " LEFT JOIN books AS book" +
  " ON author.id = book.authorId" +
  " WHERE id = :authorId")
@RegisterBeanMapper(value = Book.class, prefix = "b") 
@RegisterBeanMapper(value = AuthorWithBooks.class, prefix = "a")
@UseRowReducer(AuthorBookReducer.class) 
List<AuthorWithBooks> getAuthorWithBooks(@Bind("authorId") int authorId);

class AuthorBookReducer implements LinkedHashMapRowReducer<Integer, Author> { 
    @Override
    public void accumulate(Map<Integer, Author> map, RowView rowView) {
        Author author = map.computeIfAbsent(rowView.getColumn("a_id", Integer.class), 
                                       id -> rowView.getRow(Author.class));

        if (rowView.getColumn("b_id", Integer.class) != null) { 
            author.getBooks().add(rowView.getRow(Book.class));
        }
    }
}