如何在Spring JPA存储库中联接多个表的结果

Question

我刚接触Spring，不知道如何联接多个表来返回某个结果。我尝试实现一个小型库应用程序，如下所示。

我的实体类-预订，客户，预订

java-图书馆中的书籍

@Entity
@Table(name = "books")
public class Book {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", columnDefinition = "int")
    private int id;

    @NotNull(message = "Book name cannot be null")
    @Column(name = "book_name", columnDefinition = "VARCHAR(255)")
    private String bookName;

    @Column(name = "author", columnDefinition = "VARCHAR(255)")
    private String author;

    // getters and setters

    public Book() {}

    public Book(String bookName, String author) {
        this.bookName = bookName;
        this.author = author;
    }
}

@Entity
@Table(name = "customer", uniqueConstraints = {@UniqueConstraint(columnNames = {"phone"})})
public class Customer {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", columnDefinition = "int")
    private int id;

    @NotNull(message = "Customer name cannot be null")
    @Column(name = "name", columnDefinition = "VARCHAR(255)")
    private String name;

    @Column(name = "phone", columnDefinition = "VARCHAR(15)")
    private String phone;

    @Column(name = "registered", columnDefinition = "DATETIME")
    private String registered;

    // getters and setters

    public Customer() {}

    public Customer(String name, String phone, String registered) {
        this.name = name;
        this.phone = phone;
        this.registered = registered;
    }
}

@Entity
@Table(name = "bookings")
public class Booking {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", columnDefinition = "int")
    private int id;

    @NotNull(message = "Book id cannot be null")
    @Column(name = "book_id", columnDefinition = "int")
    private int bookId;

    @NotNull(message = "Customer id cannot be null")
    @Column(name = "customer_id", columnDefinition = "int")
    private int customerId;

    @Column(name = "issue_date", columnDefinition = "DATETIME")
    private String issueDate;

    @Column(name = "return_date", columnDefinition = "DATETIME")
    private String returnDate;

    // getters and setters

    public Booking() {}

    public Booking(int bookId, int customerId, String issueDate) {
        this.bookId = bookId;
        this.customerId = customerId;
        this.issueDate = issueDate;
    }
}

books:
+-----------+--------------+------+-----+---------+----------------+
| Field     | Type         | Null | Key | Default | Extra          |
+-----------+--------------+------+-----+---------+----------------+
| id        | int(11)      | NO   | PRI | NULL    | auto_increment |
| book_name | varchar(255) | NO   |     | NULL    |                |
| author    | varchar(255) | YES  |     | NULL    |                |
+-----------+--------------+------+-----+---------+----------------+
id - primary key

customer:
+------------+--------------+------+-----+-------------------+-------------------+
| Field      | Type         | Null | Key | Default           | Extra             |
+------------+--------------+------+-----+-------------------+-------------------+
| id         | int(11)      | NO   | PRI | NULL              | auto_increment    |
| name       | varchar(255) | NO   |     | NULL              |                   |
| registered | datetime     | YES  |     | CURRENT_TIMESTAMP | DEFAULT_GENERATED |
| phone      | varchar(15)  | YES  | UNI | NULL              |                   |
+------------+--------------+------+-----+-------------------+-------------------+
id - primary key

bookings:
+-------------+----------+------+-----+-------------------+-------------------+
| Field       | Type     | Null | Key | Default           | Extra             |
+-------------+----------+------+-----+-------------------+-------------------+
| id          | int(11)  | NO   | PRI | NULL              | auto_increment    |
| book_id     | int(11)  | NO   | MUL | NULL              |                   |
| customer_id | int(11)  | NO   | MUL | NULL              |                   |
| issue_date  | datetime | YES  |     | CURRENT_TIMESTAMP | DEFAULT_GENERATED |
| return_date | datetime | YES  |     | NULL              |                   |
+-------------+----------+------+-----+-------------------+-------------------+
id - primary key
book_id - foreign key references books.id
customer_id - foreign key references customer.id

订票员：

@RestController
@RequestMapping("/bookings")
public class BookingController {
    @Autowired
    BookingService bookingService;

    // some booking apis which return Booking objects

    @GetMapping
    public List<Booking> getAllBookingsBy(@RequestParam("phone") String phone,
                                         @RequestParam("authors") List<String> authors) {
        return bookingService.getAllBy(phone, authors);
    }

    @PostMapping
    public Booking addBooking(@RequestBody Booking booking) {
        bookingService.saveBooking(booking);
        return booking;
    }
}

预订服务类别：

@Service
public class BookingService {
    @Autowired
    private BookingRepository bookingRepository;

    // some booking service methods

    // get all bookings booked by a customer with matching phone number and books written by a given list of authors
    public List<Booking> getAllBy(String phone, List<String> authors) {
    return bookingRepository.queryBy(phone, authors);
    }

    public void saveBooking(Booking booking) {
        bookingRepository.save(booking);
    }
}

预订存储库类：

@Repository
public interface BookingRepository extends JpaRepository<Booking, Integer> {
    // some booking repository methods

    @Query(value = "SELECT * FROM bookings bs WHERE " +
            "EXISTS (SELECT 1 FROM customer c WHERE bs.customer_id = c.id AND c.phone = :phone) " +
            "AND EXISTS (SELECT 1 FROM books b WHERE b.id = bs.book_id AND b.author IN :authors)",
            nativeQuery = true)
    List<Booking> queryBy(@Param("phone") String phone,
                            @Param("authors") List<String> authors);
}

[
    {
        "id": 3,
        "book_id": 5,
        "customer_id": 2,
        "issue_date": "2019-02-04 01:45:21",
        "return_date": null
    }
]

[
    {
        "id": 3,
        "book_id": 5,
        "customer_id": 2,
        "issue_date": "2019-02-04 01:45:21",
        "return_date": null,
        "customer_name": "Cust 2",
        "book_name": "Book_2_2",
    }
]

@OneToOne
@JoinColumn(name = "book_id", insertable = false, updatable = false)
private Book book;

@OneToOne
@JoinColumn(name = "customer_id", insertable = false, updatable = false)
private Customer customer;

[
    {
        "id": 3,
        "book_id": 5,
        "book": {
            "id": 5,
            "book_name": "Book_2_2",
            "author": "author_2"
        },
        "customer_id": 2,
        "customer": {
            "id": 2,
            "name": "Cust 2",
            "phone": "98765431",
            "registered": "2019-02-04 01:13:16"
        },
        "issue_date": "2019-02-04 01:45:21",
        "return_date": null
    }
]

Answer 1

你的所作所为是错的。您正在返回Booking，并且您希望它被magicaly反序列化为一个包含连接信息的实体，比如Book Name。但是在存储库的select查询中，您已经选择了预订。在您的实现中，预订并不包含关于图书的信息。

首先，您需要将反序列化为JSON的内容和将用作spring数据持久层的内容分开。

1. 首先从预订到预订建立@onetoone/@onetomany关系。
2. 更改查询，以便对映射为book的实体/集合进行快速提取。
3. 创建一个POJO，并用JSON注解对其进行注解，以您希望控制器返回的方式对其进行注解。
4. 在您的持久性对象/Book上带有隐藏收藏的预订和新创建的POJO之间映射

@Query(value = "SELECT * FROM bookings bs WHERE " +
            "bs.customer.phone = :phone) " +
            "AND  bs.book.author IN :authors)")