如果我有一个包含另一个类的对象的实体，例如Book其内部有一个实体Publisher关联的实体如下：
@ManyToOne
@JoinColumn(name="PUB_CODE", referencedColumnName = "PUB_CODE")
private Publisher pub;
这是一种安全/正确的方法（我在本示例中看到了数据库中的正确数据，但不能 100% 确定它是否适用于所有情况）方法来发布在数据库中具有外键关联的对象？我不知道这在事务原子性或线程方面是否安全，或者是否有效。相关代码如下：
书本.java
package app.domain;
/*imports*/
@Entity
public class Book implements Serializable{
/**
*
*/
private static final long serialVersionUID = -6902184723423514234L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@Column(nullable = false, unique=true)
private String bookName;
@Column(nullable = false)
private int pageCount;
@ManyToOne
@JoinColumn(name="PUB_CODE", referencedColumnName="PUB_CODE")
private Publisher pub;
/*public getters and setters*/
}
发布者.java
package app.domain;
/*imports*/
@Entity
public class Publisher implements Serializable {
private static final long serialVersionUID = 4750079787174869458L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@Column(name="PUB_CODE",nullable = false, unique = true)
private String publisherCode;
@Column(nullable = false)
private String publisherName;
/*public getters and setters*/
}
BookRepo.java
package app.service;
/*imports*/
public interface BookRepo extends JpaRepository<Book, Long>{
@Query("SELECT pb FROM Publisher pb WHERE pb.publisherCode = TRIM(UPPER(:pubCode))")
public Publisher findPublisherByPubCode(@Param("pubCode")String pubCode);
}
BookController.java
package app.controller;
/*imports*/
@RestController
@RequestMapping(value = "/books")
public class BookController {
private BookRepo bookRepo;
@Autowired
public BookController(BookRepo bookRepo) {
this.bookRepo = bookRepo;
}
//The ApiPathParam is for JSONDOC purposes
@RequestMapping(value = "/create", method = RequestMethod.POST)
public List<Book> create(@ApiPathParam(name = "book") @RequestBody Book book, @ApiPathParam(name = "pubCode") @RequestParam("pubCode") String pubCode) {
// Assume exception handling
Publisher pbToAttachToThisBook = bookRepo.findPublisherByPubCode(pubCode);
book.setPub(pbToAttachToThisBook);
bookRepo.save(book);
return bookRepo.findAll();
}
}
Post 对象主体（输入到 POST 工具中）：
{
"bookName": "goosebumps",
"id": 0,
"pageCount": 332,
"pub": {
"id": 0,
"publisherCode": "",
"publisherName": "",
"serialVersionUID": 0
},
"serialVersionUID": 0
}
提供的 pubCode 参数输入，也输入到 POST 工具中，与上面的调用相同: 'SC'
执行完上面的代码后，在Book表中，就有了上面这本书的条目，其PUB_CODE外键列填写为'SC'，以及返回的List<Book>调用的 POST 控制器方法显示新添加的书籍包括Publisher出版商的实体信息（例如全名“Scholastic”）PUB_CODE='SC'该信息已经存在于数据库中。
谢谢。
