Spring Data JPA中EmbeddedId含自增字段，保存后无法获取ID值

我有一个Customer实体，主键是复合键，其中的id字段为自动生成值。实体类及嵌入式主键类代码如下：

@Entity
@AllArgsConstructor
@Builder
@Setter
@Getter
public class Customer {
 
  @EmbeddedId
  private CustomerId customerId;

  @Size(max = 255)
  @Column(name = "first_name")
  private String firstName;
}

@Embeddable
@Getter
@Setter
@Builder
@NoArgsConstructor
@AllArgsConstructor
@EqualsAndHashCode
public class CustomerId implements Serializable {
  private static final long serialVersionUID = 8048935613697415032L;
  @NotNull
  @Column(name = "account_id", nullable = false)
  private Long accountId;

  @NotNull
  @Column(name = "id", nullable = false)
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
}

使用以下代码保存Customer时，数据库成功写入记录，但无法获取saved.getCustomerId().getId()的值（返回null），尝试过EmbeddedId和IdClass均无效，求解决办法：

@PostMapping
public ResponseEntity create(@RequestBody Customer sc,
                             @RequestParam long account_id) {
  sc.setCustomerId(CustomerId.builder().accountId(account_id).build());
  Customer saved = customerRepository.saveAndFlush(sc);
  return ResponseEntity.ok(saved);
}

问题原因 #

JPA规范中，嵌入式主键（@EmbeddedId）内的字段不支持直接使用@GeneratedValue，这是因为嵌入式主键被视为一个整体，JPA不会单独对其中的字段进行自动生成值的回填操作。

解决办法 #

方案1：拆分主键字段，使用@IdClass+单独标注自动生成ID #

把自动生成的id从嵌入式主键中拆分出来，作为实体的单独主键字段，同时保留accountId作为另一个主键字段，使用@IdClass定义复合主键：

1. 定义主键类CustomerId（移除@GeneratedValue）：

@Getter
@Setter
@Builder
@NoArgsConstructor
@AllArgsConstructor
@EqualsAndHashCode
public class CustomerId implements Serializable {
    private static final long serialVersionUID = 8048935613697415032L;
    private Long accountId;
    private Long id;
}

2. 修改Customer实体类：

@Entity
@AllArgsConstructor
@Builder
@Setter
@Getter
@IdClass(CustomerId.class)
public class Customer {
    @Id
    @NotNull
    @Column(name = "account_id", nullable = false)
    private Long accountId;

    @Id
    @NotNull
    @Column(name = "id", nullable = false)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Size(max = 255)
    @Column(name = "first_name")
    private String firstName;
}

3. 调整保存逻辑：

@PostMapping
public ResponseEntity create(@RequestBody Customer sc,
                             @RequestParam long account_id) {
    sc.setAccountId(account_id);
    // id由数据库自动生成，无需手动设置
    Customer saved = customerRepository.saveAndFlush(sc);
    return ResponseEntity.ok(saved);
}

方案2：使用@MapsId关联单独的自动生成字段（保留嵌入式主键结构） #

如果希望保留嵌入式主键的结构，可以通过单独的字段承载自动生成值，再用@MapsId映射到嵌入式主键中：

1. 修改CustomerId（移除@GeneratedValue）：

@Embeddable
@Getter
@Setter
@Builder
@NoArgsConstructor
@AllArgsConstructor
@EqualsAndHashCode
public class CustomerId implements Serializable {
    private static final long serialVersionUID = 8048935613697415032L;
    @NotNull
    @Column(name = "account_id", nullable = false)
    private Long accountId;

    @NotNull
    @Column(name = "id", nullable = false)
    private Long id;
}

2. 修改Customer实体类：

@Entity
@AllArgsConstructor
@Builder
@Setter
@Getter
public class Customer {
    @EmbeddedId
    private CustomerId customerId;

    // 单独定义自动生成的id字段，映射到嵌入式主键的id属性
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", insertable = false, updatable = false)
    @MapsId("id")
    private Long generatedId;

    @Size(max = 255)
    @Column(name = "first_name")
    private String firstName;
}

3. 调整保存逻辑：

@PostMapping
public ResponseEntity create(@RequestBody Customer sc,
                             @RequestParam long account_id) {
    sc.setCustomerId(CustomerId.builder().accountId(account_id).build());
    Customer saved = customerRepository.saveAndFlush(sc);
    // 此时saved.getCustomerId().getId()会被正确回填，也可直接获取saved.getGeneratedId()
    return ResponseEntity.ok(saved);
}

内容的提问来源于stack exchange，提问作者Arul Pragasam