spring mongodb - 聚合管道到java

Question

我编写了以下聚合管道，它返回我的用户集合中最喜欢的项目

db.users.aggregate([
  {$unwind: "$favoriteItems"},
  {$group: {
    _id: "$favoriteItems" ,
    likes: { $sum: 1 }
  }},
  {$sort: { likes: -1 }}
])

这是我的用户收藏中的一个原型文档：

{
  "_id": "5a6df13552f42a34dcca9aa6",
  "username": "user1",
  "favoriteItems": [
    {
      "_id": "5a0c6b2dfd3eb67969316d6d",
      "name": "item1"
    },
    {
      "_id": "5a0c680afd3eb67969316d0b",
      "name": "item2"
    }
  ]
}

这是我在 java 中做同样的尝试：

public void getMostLikedItems () {
        UnwindOperation unwind = Aggregation.unwind("favoriteItems");
        GroupOperation group = Aggregation.group("favoriteItems").sum("1").as("likes");
        SortOperation sort = Aggregation.sort(Sort.Direction.DESC, "likes");

        Aggregation aggregation = newAggregation(unwind, group, sort);
        AggregationResults<LikedItem > result = mongoTemplate.aggregate(aggregation, "users", LikedItem .class);
        for (LikedItem s: result) {
            System.out.println(s.getId() + ": " + s.getValue());
        }
    }

这不会产生任何输出。我在这里错过了什么？

编辑 LikedItem.java

public class LikedItem {

    private Item id;
    private float value;
    // empty and full constructor + getters and setters

}

编辑 2 物品类别

public class Item{
    @Id
    private String id;
    private String name;
    private String city;
    @GeoSpatialIndexed(type= GeoSpatialIndexType.GEO_2DSPHERE)
    private GeoJsonPoint location;

    public Shop() { super(); }
    // full constructor + getters and setters
}

Answer 1

您使用的方法不正确。

sum 方法被引用，你会得到类似"likes" : { "$sum" : "$1" } 的东西。

改用count方法输出"likes" : { "$sum" : 1 }

GroupOperation group = Aggregation.group("favoriteItems").count().as("likes");