使用为数组中的MongoDB子文档自动生成ID

Question

我的MongoDB post文档结构如下所示

{
"_id" : ObjectId("5e487ce64787a51f073d0915"),
"active" : true,
"datePosted" : ISODate("2020-02-15T23:21:10.329Z"),
"likes" : 400,
"commentList" : [ 
    {
        "datePosted" : ISODate("2020-02-15T23:21:10.329Z"),
        "comment" : "I read all your posts and always think they don't make any sense",
        "likes" : 368
    }, 
    {
        "datePosted" : ISODate("2020-02-15T23:21:10.329Z"),
        "comment" : "I enjoy all your posts and are great way to kill time",
        "likes" : 3533
    }
}

还有相应的实体类

CommentEntity.java

public class CommentEntity{

  private String id;
  private LocalDateTime datePosted;
  private String comment;
  private int likes;

  ....

}

PostEntity.java

@Document(collection = "post")
public class PostEntity {

  @Id
  private String id;
  private boolean active;
  private LocalDateTime datePosted;
  private int likes;
  private List<CommentEntity> commentList;

  ....

}

我使用Spring MongoTemplate作为插入。当注释插入到MongoTemplate文档中时，如何配置_id自动生成注释，如下所示

{
"_id" : ObjectId("5e487ce64787a51f073d0915"),
"active" : true,
"datePosted" : ISODate("2020-02-15T23:21:10.329Z"),
"likes" : 400,
"commentList" : [ 
    {
        "_id" : ObjectId("5e487ce64787a51f07snd315"),
        "datePosted" : ISODate("2020-02-15T23:21:10.329Z"),
        "comment" : "I read all your posts and always think they don't make any sense",
        "likes" : 368
    }, 
    {
        "_id" : ObjectId("5e48764787a51f07snd5j4hb4k"),
        "datePosted" : ISODate("2020-02-15T23:21:10.329Z"),
        "comment" : "I enjoy all your posts and are great way to kill time",
        "likes" : 3533
    }
}

Answer 1

Spring数据将类映射到MongoDB文档中。在映射过程中，只能自动生成_id。

MongoDB要求所有文档都有一个“_id”字段。如果不提供一个，驱动程序将为ObjectId分配一个生成值。带有@Id (org.springframework.data.annotation.Id)注释的字段将映射到“_id”字段。

没有注释但名为id的字段将映射到_id字段。

https://docs.spring.io/spring-data/mongodb/docs/current/reference/html/#mapping.conventions.id-field

解决办法：

实例新的ObjectId用于id字段和约定将id转换为_id。

public class CommentEntity {

    private String id;
    private LocalDateTime datePosted;
    private String comment;
    private int likes;

    ....

    public CommentEntity() {
        id = new ObjectId().toString();
        ...
    }

}