嘿，我想创建一个扩展JpaRepository的存储库并获取结果而无需编写实际查询，在我的示例中，我有2个表Book和Author，它们之间存在多对多关系，假设我想按特定的author_id来获取图书清单，因为在我图书实体，我没有任何名为author_id的字段，因此我将如何使用JPARepository来获取结果而无需编写实际查询。我正在做这样的事情：我创建了一个BookDTO，其中包含Book和Author的对象，并且我创建了bookDTORepository来扩展JpaRepository并正在调用List<Book> findByAuthor_Id(Integer id);，但是它的抛出错误为：Not an managed type: class golive.data.bookdto我的书类是

package golive.data;



import java.util.ArrayList;

import java.util.HashSet;

import java.util.List;

import java.util.Set;



import javax.persistence.CascadeType;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.FetchType;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.JoinTable;

import javax.persistence.ManyToMany;

import javax.persistence.ManyToOne;

import javax.persistence.Table;

import javax.persistence.Transient;



import com.fasterxml.jackson.annotation.JsonIgnore;

import com.sun.istack.internal.NotNull;



@Entity

@Table(name="book")

public class Book implements java.io.Serializable{



    @Id

    @GeneratedValue

    private Integer id;



    @NotNull

    @Column(name="name")

    private String name;





    @ManyToMany(cascade = CascadeType.ALL,fetch = FetchType.LAZY)

    @JoinTable(name = "writes", joinColumns = { @JoinColumn(name = "book_id") }, inverseJoinColumns = { @JoinColumn(name = "author_id") })

    private Set<Author> authors = new HashSet<Author>();





    public Set<Author> getAuthors() {

        return authors;

    }



    public Integer getId() {

        return id;

    }



    public String getName() {

        return name;

    }



    public void setAuthors(Set<Author> authors) {

        this.authors = authors;

    }



    public void setId(Integer id) {

        this.id = id;

    }



    public void setName(String name) {

        this.name = name;

    }





}

我的作家班是

package golive.data;



import java.util.ArrayList;

import java.util.HashSet;

import java.util.List;

import java.util.Set;



import javax.persistence.CascadeType;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.FetchType;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.JoinTable;

import javax.persistence.ManyToMany;

import javax.persistence.OneToMany;

import javax.persistence.OneToOne;

import javax.persistence.Table;

import javax.persistence.UniqueConstraint;



import com.fasterxml.jackson.annotation.JsonIgnore;

import com.sun.istack.internal.NotNull;



@Entity

@Table(name="author")

public class Author implements java.io.Serializable{



    @Id

    @GeneratedValue

    @Column(name="id")

    private Integer Id;



    @NotNull

    @Column(name="name")

    private String name;





    public Integer getId() {

        return Id;

    }



    public String getName() {

        return name;

    }







    public void setId(Integer id) {

        Id = id;

    }



    public void setName(String name) {

        this.name = name;

    }



}

我预定的课程是

package golive.data;



public class bookdto {



    private Book book;

    private Author author;

    public Book getBook() {

        return book;

    }

    public void setBook(Book book) {

        this.book = book;

    }

    public Author getAuthor() {

        return author;

    }

    public void setAuthor(Author author) {

        this.author = author;

    }



}

我的bookDTORepository是：

package golive.data;



import java.util.List;



import org.springframework.data.jpa.repository.JpaRepository;



public interface bookDTORepository extends JpaRepository<bookdto, Book> {



    List<Book> findByAuthor_Id(Integer id);



}

我添加了书控制器方法：

    @RequestMapping(value = "/listbyauthor", method = RequestMethod.POST, produces = "application/json")

    public ResponseEntity<List<Book>> getBookByAuthorId(@RequestBody Author author,HttpServletResponse response) {

        try {

            Author temp = new Author();

            temp.setId(author.getId());

            temp.setName(author.getName());

            return new ResponseEntity<>(bookRepository.findByAuthor(temp), HttpStatus.OK);

        } catch (Exception e) {

            e.printStackTrace();

        }

        return new ResponseEntity<>(HttpStatus.NO_CONTENT);

    }