java - 如何创建 QClass ，没有实体或与 QueryDSL 中的两个表关联

Question

假设我有三个类(class)

    @Entity
    public class Book {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Long id;

        @Column
        private String name;
    }

    @Entity
    public class Author {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Long id;

        @Column
        private String fistName;

        @Column
        private String lastName;
    }

    @Entity
    public class AuthorBookRelation {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Long id;

        @ManyToOne
        @JoinColumn(name = "author", referencedColumnName = "id")
        private Author author;

        @ManyToOne
        @JoinColumn(name = "book", referencedColumnName = "id")
        private Book book;
    }

因此，我有三个 Qclasses

QAuthor QBook QAuthorBookRelation。

但我只能上两个类。

@Entity
    public class Book {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Long id;

        @Column
        private String name;
    }

    @Entity
    public class Author {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Long id;

        @Column
        private String fistName;

        @Column
        private String lastName;

        @ManyToMany
        @JoinTable(
                name = "author_book_relation",
                joinColumns = {@JoinColumn(name = "author")},
                inverseJoinColumns = {@JoinColumn(name = "book")}
        )
        private List<Book> books = new ArrayList<>();
    }

那么就不需要 AuthorBookRelation 类了。但我需要 QAuthorBookRelation 来使用 queryDSL 创建请求

如何创建一个绑定(bind)到两个表的类？

Answer 1

我认为您没有捕获 JPA、JPQL 和 QueryDSL 的重点。您应该加入关联实体。这些技术中绝对不需要关联实体，除非您需要将数据与此关联关联起来。

否则，你只需这样做:

List<Tuple> result = query().from(QBook.book)
     .innerJoin(QBook.book.author, author)
     .select(QBook.book, QAuthor.author)
     .fetch();

这相当于以下 JPQL:

SELECT book, author FROM Book book INNER JOIN book.author author