java - 使用 Spring MongoTemplate 自动生成数组中 MongoDB 子文档的 ID

Question

我的 post MongoDB 文档结构是这样的

{
"_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
    }
}

还有对应的实体类

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;

  ....

}

我正在使用 Spring Data MongoTemplate 进行插入。如何配置 MongoTemplate 在将注释插入 post 文档时自动生成 _id 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 Data 将您的类映射到 MongoDB 文档。映射过程中，只能自动生成_id。

MongoDB requires that you have an '_id' field for all documents. If you don't provide one the driver will assign a ObjectId with a generated value. A field annotated with @Id (org.springframework.data.annotation.Id) will be mapped to the '_id' field.

A field without an annotation but named id will be mapped to the _id field.

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

解决方法:

为 id 字段和约定实例新的 ObjectId 会将 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();
        ...
    }

}