英文:
JPA not generating Id for entity
问题
我有以下的类：
@Entitypublic 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());}}
我从HTTP请求中获取一个包含文本和创建者ID的CommentDto。
据我理解，commentId应该通过调用空构造函数来生成。
在我的Service中，我做了以下操作：
public void addComment(CommentDto comment) {Comment commentEntity = new Comment(comment);commentRepository.save(commentEntity);}
其中commentRepository是一个自动装配的JpaRepository<Comment, Long>。
问题是，ID没有生成，我尝试将一个具有空ID的对象插入我的数据库中，从而导致错误。
英文:
I have the following class
@Entitypublic 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.
答案1
得分: 6
@GeneratedValue(strategy = GenerationType.IDENTITY)
你正在使用 GenerationType.IDENTITY，这意味着使用 IdentityGenerator，它期望数据库中的自增列生成的值，也就是自动递增的。在数据库中将主键设置为自动递增以解决此问题。
或者，你可以使用 GenerationType.AUTO，这是默认的策略。在提交时，AUTO 策略使用全局编号生成器为每个新的实体对象生成主键。这些生成的值在数据库级别是唯一的，永远不会被重新使用。
@Id
@GeneratedValue
@Column(name = "comment_id")
private Long commentId;
英文:
@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;
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