在hql查询中使用新的构造函数无法找到正确的consturctor或无法提取ResultSet

Question

我有实体：

@Entity
public class Author{
    @ManyToMany(cascade = { CascadeType.ALL })
    @JoinTable(
            name = "author_book",
            joinColumns = { @JoinColumn(name = "author_id") },
            inverseJoinColumns = { @JoinColumn(name = "book_id") }
    )
   public List<Book> books;
}

@Entity
public class Book{
   @ManyToMany(mappedBy = "books")
   public List<Author> authors;

   @OneToMany(mappedBy = "book")
   public List<Fact> facts;

   public Book(){}
   public Book(List<Author> authors, List<Fact> facts){
       this.authors = authors;
       this.facts = facts;
   }
}

@Entity class Fact{
   @ManyToOne
   @JoinColumn(name="book_id")
   public Book book;
}

书有更多的作者，作者可以写更多的书。每本书都有更多关于它的事实，每一个行为只属于一本书。

List<Book> books = (List<Book>) session.createQuery("Select new Book (books.authors, books.facts ) FROM Author u JOIN u.books books JOIN books.facts WHERE u.id IN :ids ").setParameter("ids", authorId).list();

但它会导致错误：

在类[Book]上找不到适当的构造函数。预期的参数为：java.util.Collection、java.util.Collection

我曾尝试调整构造函数以获取对象或集合，并自己进行强制转换：

   public Book(Object authors,Object facts){
       this.authors = (List<Author>)authors;
       this.facts = (List<Fact>)facts;
   }

Answer 1

您不能将新运算符与实体一起使用！

这是用于DTO（数据传输对象）投影的。

在您的例子中，您甚至不需要新的，因为您可以简单地选择将由Hibernate使用默认构造函数并设置字段构建的book。

List<Book> books = 
   (List<Book>) session.createQuery(
   "Select books FROM Author u JOIN u.books books JOIN books.facts WHERE u.id IN :ids ")
   .setParameter("ids", authorId).list();

List<Book> books = 
   (List<Book>) session.createQuery(
   "Select b FROM Book b JOIN FETCH b.authors a JOIN FETCH b.facts f WHERE a.id IN :ids ")
   .setParameter("ids", authorId).list();

Hibernate无法急切地获取两个列表。在这里，我建议将列表更改为集合：

@ManyToMany(mappedBy = "books")
public Set<Author> authors;

@OneToMany(mappedBy = "book")
public Set<Fact> facts;