Java 如何使用Hibernate仅从两个单独的表返回两个字段？

如何使用下面的类返回以下JSON，而不返回

userId

和

bookId

？我尝试过各种不同的查询，但都没有得到预期的结果。它不必完全匹配json名称。我只想要一个用户名和一个要归还的书籍列表

请参阅存储库

@Query

{
   "userName": "jamesbond007",
   "books": [
       "Cat In the Hat",
       "Green Eggs and Ham
   ]
}

Users.java:

@Getter
@Entity
@Table(name = "users")
public class User {
    @Id
    @OneToMany
    @JoinColumn(name = "user_id")
    private Integer userId;
    
   @Column(name = "user_name")
    private String userName;
}

@Getter
@Entity
@Table(name = "books")
public class Books {
    @Id
    @OneToMany
    @JoinColumn(name = "book_id") 
    private Integer bookId;

    @Column(name = "book_name")
    private String bookName;
}

@Getter
@Entity
@Table(name = "user_books")
public class UserBooks{
    @Id
    @Column(name = "user_book_id")
    private Integer userBookId;
    
    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user
    
    @ManyToOne
    @JoinColumn(name = "book_id")
    private Book book;
}

public interface MyRepository extends JPARepository<UserBooks, Integer> {
     @Query("SELECT ub.userName, ub.bookName FROM UserBooks ub JOIN ub.User JOIN ub.Book WHERE userId=?1") //WHAT DO I DO HERE?
     UserBooks getAllBooksByUser(Integer userId);
}

Books.java:

@Getter
@Entity
@Table(name = "users")
public class User {
    @Id
    @OneToMany
    @JoinColumn(name = "user_id")
    private Integer userId;
    
   @Column(name = "user_name")
    private String userName;
}

@Getter
@Entity
@Table(name = "books")
public class Books {
    @Id
    @OneToMany
    @JoinColumn(name = "book_id") 
    private Integer bookId;

    @Column(name = "book_name")
    private String bookName;
}

@Getter
@Entity
@Table(name = "user_books")
public class UserBooks{
    @Id
    @Column(name = "user_book_id")
    private Integer userBookId;
    
    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user
    
    @ManyToOne
    @JoinColumn(name = "book_id")
    private Book book;
}

public interface MyRepository extends JPARepository<UserBooks, Integer> {
     @Query("SELECT ub.userName, ub.bookName FROM UserBooks ub JOIN ub.User JOIN ub.Book WHERE userId=?1") //WHAT DO I DO HERE?
     UserBooks getAllBooksByUser(Integer userId);
}

UserBooks.java:

@Getter
@Entity
@Table(name = "users")
public class User {
    @Id
    @OneToMany
    @JoinColumn(name = "user_id")
    private Integer userId;
    
   @Column(name = "user_name")
    private String userName;
}

@Getter
@Entity
@Table(name = "books")
public class Books {
    @Id
    @OneToMany
    @JoinColumn(name = "book_id") 
    private Integer bookId;

    @Column(name = "book_name")
    private String bookName;
}

@Getter
@Entity
@Table(name = "user_books")
public class UserBooks{
    @Id
    @Column(name = "user_book_id")
    private Integer userBookId;
    
    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user
    
    @ManyToOne
    @JoinColumn(name = "book_id")
    private Book book;
}

public interface MyRepository extends JPARepository<UserBooks, Integer> {
     @Query("SELECT ub.userName, ub.bookName FROM UserBooks ub JOIN ub.User JOIN ub.Book WHERE userId=?1") //WHAT DO I DO HERE?
     UserBooks getAllBooksByUser(Integer userId);
}

存储库：

@Getter
@Entity
@Table(name = "users")
public class User {
    @Id
    @OneToMany
    @JoinColumn(name = "user_id")
    private Integer userId;
    
   @Column(name = "user_name")
    private String userName;
}

@Getter
@Entity
@Table(name = "books")
public class Books {
    @Id
    @OneToMany
    @JoinColumn(name = "book_id") 
    private Integer bookId;

    @Column(name = "book_name")
    private String bookName;
}

@Getter
@Entity
@Table(name = "user_books")
public class UserBooks{
    @Id
    @Column(name = "user_book_id")
    private Integer userBookId;
    
    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user
    
    @ManyToOne
    @JoinColumn(name = "book_id")
    private Book book;
}

public interface MyRepository extends JPARepository<UserBooks, Integer> {
     @Query("SELECT ub.userName, ub.bookName FROM UserBooks ub JOIN ub.User JOIN ub.Book WHERE userId=?1") //WHAT DO I DO HERE?
     UserBooks getAllBooksByUser(Integer userId);
}

公共接口MyRepository扩展了JPARepository{
@查询（“从UserBooks ub JOIN ub.User JOIN ub.Book WHERE userId=？1中选择ub.userName，ub.bookName”）//我在这里做什么？
UserBooks getAllBooksByUser（整数用户ID）；
}

我想问两个问题。一个用来获取用户的用户名，另一个用来获取他所有的书。 然后我将创建一个DTO（数据传输对象），它只保留我需要的数据

e、 g:

公共类MyDto
{
字符串用户名；
书单；
//吸气剂二传手
}

然后执行回购以获取此用户的所有书籍：

公共接口BookRepo扩展了JPARepository{
@查询（“选择b.*从u.User\u id=ub.User\u id在u.User\u id=ub.Book\u id中的用户加入用户，其中u.User\u id=1”，nativeQuery=true）
列出getAllBooksByUserId（整数用户ID）；
}

服务的一个简单场景是：

getUsernameAndBooks（int-userId）
{
User User=userRepo.findById（userId）；
List booksList=bookRepository.getAllBooksByUserId（userId）；
返回新的MyDto（user.getUsername（），booksList）
}

映射有问题，不清楚是双向关联还是单向关联。 请注意，在这两种情况下，您都可以获得所需的信息，但查询会发生一些变化

由于您尝试使用了

@OneToMany

注释，因此我假定您正在尝试创建双向关联：

    @Entity
    @Table(name = "users")
    public class User {
        @Id
        @Column(name = "user_id")
        private Integer userId;

        @Column(name = "user_name")
        private String userName;
        
        @OneToMany(mappedBy="user")
        private Set<UserBooks> books = new HashSet<>();
    }

    @Entity
    @Table(name = "books")
    public class Book {
        @Id
        @Column(name = "book_id")
        private Integer bookId;

        @Column(name = "book_name")
        private String bookName;
        
        @OneToMany(mappedBy="book")
        private Set<UserBooks> users = new HashSet<>();
    
    }

    @Entity
    @Table(name = "user_books")
    public class UserBooks{
        @Id
        @Column(name = "user_book_id")
        public Integer userBookId;

        @ManyToOne
        @JoinColumn(name = "user_id")
        public User user;

        @ManyToOne
        @JoinColumn(name = "book_id")
        private Book book;
    }

而查询将变成：

public interface MyRepository extends JPARepository<User, Integer> {
     @Query("FROM User u JOIN FETCH u.books WHERE u.userId=?1")
     User getAllBooksByUser(Integer userId);
}

公共接口MyRepository扩展了JPARepository{
@查询（“从用户u加入获取u.books，其中u.userId=？1”）
用户getAllBooksByUser（整数用户ID）；
}

我就让你去冬眠吧