spring数据mongo文档中的计算字段

我有两个非常简单的实体，Post和Comments带有1->*“relation”

以下是我的实体：

@Document
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Comment {

  @Id
  private String id;

  @JsonProperty(access = READ_ONLY)
  @Indexed
  private String postId;

  @NotEmpty
  @Length(max = 300)
  private String description;

  @JsonProperty(access = READ_ONLY)
  private Instant createdDate;
}

@Document
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Post {

  @Id
  @JsonProperty(access = READ_ONLY)
  private String id;

  @NotEmpty
  @Length(max = 300)
  private String title;

  @NotEmpty
  private String description;

  @JsonProperty(access = READ_ONLY)
  private Instant createdDate;

  @JsonProperty(access = READ_ONLY)
  private Instant updatedDate;

  @JsonProperty(access = READ_ONLY)
  private Long commentsCount = 0L;

}

---

正如你所看到的，我的帖子实体有一个“commentscont”字段，这就是你所认为的。在通过post存储库获取单个post实例/post列表时，是否可以填充此字段？好的，我知道我正在通过评论库对每个帖子的数量进行额外的查询，但对于20篇帖子，我的响应时间从10毫秒增加到了30-40毫秒。

通过存储库方法是不可能的。您需要对此进行聚合

差不多

LookupOperation lookupOperation = LookupOperation.newLookup().from("post").localField("_id").foreignField("postId").as("comments");
ProjectionOperation projectionOperation = project("title", "description", "createdDate", "updatedDate").and("comments").size().as("commentsCount");
Aggregation agg = Aggregation.newAggregation(lookupOperation, projectionOperation);
List<Post> results = mongoOperations.aggregate(agg, "posts", Post.class).getMappedResults();

LookupOperation LookupOperation=LookupOperation.newLookup（）.from（“post”）.localField（“_id”）.foreignField（“postId”）.as（“comments”）；
ProjectionOperation ProjectionOperation=项目（“标题”、“说明”、“创建日期”、“更新日期”）和（“注释”）.size（）.as（“注释”）；
Aggregation agg=Aggregation.newAggregation（lookupOperation，projectionOperation）；
List results=mongoOperations.aggregate（agg，“posts”，Post.class）.getMappedResults（）；