java - Spring Boot、MongoDB、Pageable、按对象中的自定义方法排序

Question

例如，我有以下设置，

这样的模型:

public class Post {

    @Id
    private String id;
    private String post;
    private List<Vote> votes = new ArrayList<>();

    // Getters & Setters...
    public double getUpVotes() {
        return votes.stream().filter(vote -> vote.getDirection() == 1).mapToInt(Vote::getDirection).count();
    }
}

和

public class Vote {

    private short direction;

    // Getters & Setters...
}

然后是像这样的存储库

@Repository
public interface PostRepository extends PagingAndSortingRepository<Post, String> {

    List<Post> findAll(Pageable pageable);
}

并假设我想根据 getter 方法的结果对帖子进行排序 getUpVotes()

我已尝试以下 localhost:3005/opinion?page=0&size=20&sort=upVotes 但它不起作用。

Answer 1

The sort document can specify ascending or descending sort on existing fields ...

https://docs.mongodb.com/manual/reference/method/cursor.sort/#sort-asc-desc

解决方法:您可以执行 MongoDB aggregation您可以在其中添加具有计算值的新字段并按该值排序:

db.post.aggregate([
  {
    $addFields: {
      upVotes: {
        $size: {
          $filter: {
            input: "$votes.direction",
            cond: {
              $eq: [ "$$this", 1 ]
            }
          }
        }
      }
    }
  },
  {
    $sort: {
      upVotes: 1
    }
  }
])

MongoPlayground | $project

Spring 数据

@Autowired
private MongoTemplate mongoTemplate;
...

Aggregation aggregation = Aggregation.newAggregation(addFields, sort);
List<Post> result = mongoTemplate
                       .aggregate(aggregation, mongoTemplate.getCollectionName(Post.class), Post.class)
                       .getMappedResults();