我是Spring的新手，我无法弄清楚如何联接多个表以返回一些结果。我试图实现一个小型的Library应用程序，如下所示。
我的实体类别-图书，客户，预订
Book.java-图书馆中可用的图书
@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;
}
}
Customer.java-在库中注册的客户
@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;
}
}
Booking.java-客户进行的所有预订
@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;
}
}
现在，各个实体的表架构如下：
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
现在，我想做的是得到一些预订标准，例如客户电话或作者姓名等，我想退回与该订单有关的所有预订。我将显示一个示例Booking API进行解释。
预订控制器：
@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;
}
}
Booking Service类：
@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);
}
现在点击显示的预订控制器将返回一个看起来像这样的预订对象：
[
{
"id": 3,
"book_id": 5,
"customer_id": 2,
"issue_date": "2019-02-04 01:45:21",
"return_date": null
}
]
但是我不想这样，我想和他们一起返回预订的客户名和书名。因此，我希望控制器返回的预订对象看起来像这样：
[
{
"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",
}
]
有人可以帮忙吗？我被困住了，因为我无法从这里继续。
＃编辑： 我在预订类中添加了这些单向的onetoone关联：
@OneToOne
@JoinColumn(name = "book_id", insertable = false, updatable = false)
private Book book;
@OneToOne
@JoinColumn(name = "customer_id", insertable = false, updatable = false)
private Customer customer;
但是现在当我击中控制器时，我将整个Book和Customer对象放入Booking对象中。那么，如何在预订对象中返回书名和客户名呢？这是我的预订对象返回的样子：
[
{
"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
}
]
现在我的预订控制器中的save（）api也无法正常工作，因为当我向其发送类型为Booking的对象时，bookId和customerId以某种方式变为0，这在我之前没有发生添加了这些更改。
答案 0 :(得分：0)
您拥有的查询不是联接表的最佳方法。 更直观的方式就是这样
{{1}}
答案 1 :(得分：0)
您所做的是错误的。您正在返回预订，并且希望它神奇地反序列化为包含诸如书名之类的联接信息的实体。但是，在对存储库的选择查询中，您已经选择了预订。实施过程中的方式预订不包含有关预订的信息。
首先，您需要分离将反序列化为JSON的内容和将用作对Spring数据的持久化层的内容。
1.Make a @OneToOne/@OneToMany relationship from Booking to Book as a start.
2.Change your query to do eager fetching on the entity/collection you have mapped as Book.
3. Make a POJO and annotate it with JSON annotations the way you want it to be returned by the controller.
4. Map between your persistence object / Booking with hidrated collection on Book and your newly created POJO
如果将其映射为OneToOne，则默认初始化为EAGER，因此查询变得有点不必要。
如果我们假设您在持久层中具有正确的映射，则查询将如下所示：
@Query(value = "SELECT * FROM bookings bs WHERE " +
"bs.customer.phone = :phone) " +
"AND bs.book.author IN :authors)")
这是您来自Hibernate的映射文档> http://docs.jboss.org/hibernate/orm/5.4/userguide/html_single/Hibernate_User_Guide.html#associations
答案 2 :(得分：0)
您可以按照以下步骤实施。
有关更多信息，您可以参考Spring数据表中的Projections。 https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#projections