JPA 没有为实体生成 Id

Question

I have the following class

  @Entity
  public class Comment {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "comment_id")
    private Long commentId;

    @Column(name = "creator_id")
    private Long creatorId;

    @Column(name = "text")
    @ApiModelProperty(value = "Text des Kommentar")
    private String text;

    @Column(name = "timestamp")
    @ApiModelProperty(value = "Zeitstempel der letzten Bearbeitung")
    private String timestamp;


    protected Comment() {}
    
    public Comment(CommentDto dto) {
      this();
      updateComment(dto);
    }

    private void updateComment(CommentDto dto) {
      setText(dto.getText());
      setCreatorId(dto.getCreatorId());
      setTimestamp(UtilService.getTimestampString());
    }

I get a CommentDto from my HTTP-Request consisting of a the text and the creatorId.

As far as I understand, the commentId should be generated through the call of the empty constructor.

In my Service I do the following

public void addComment(CommentDto comment) {
  Comment commentEntity = new Comment(comment);
  commentRepository.save(commentEntity);
}

With commentRepository being an Autowired JPARepository<Comment, Long>

The problem is, that the ID does not get generated and I get an error for trying to insert an object into my DB with a null id.

Answer 1

@GeneratedValue(strategy = GenerationType.IDENTITY)

You are using GenerationType.IDENTITY that means IdentityGenerator which expects values generated by an identity column in the database, meaning they are auto-incremented. Make the primary key auto-incremented in database to solve this.

Or you can use GenerationType.AUTO which is the default strategy. During a commit, the AUTO strategy uses the global number generator to generate a primary key for every new entity object. These generated values are unique at the database level and are never recycled.

@Id
@GeneratedValue
@Column(name = "comment_id")
private Long commentId;