放卷后弹簧组操作 - 找不到$first或$push

Question

>我有文章和标签集合。文章包含标签，这是对象ID数组。我也想获取 tagName，所以我展开（这给了我多行 - 每个标签数组条目 1 行）=> 查找（与选项卡集合连接）=>组（将其合并到原始结果集中）

我的 mongodb 查询如下，它给了我正确的结果：

db.articles.aggregate([
  {"$unwind": "$tags"},
  {
    "$lookup": {
      "localField": "tags",
      "from": "tags",
      "foreignField": "_id",
      "as": "materialTags"
    }
 },
 {
    "$group": {
      "_id": "$_id",
      "title": {"$first": "$title"},
      "materialTags": {"$push": "$materialTags"}
    }
  }
])

我相应的弹簧代码：

UnwindOperation unwindOperation = Aggregation.unwind("tags");
LookupOperation lookupOperation1 = LookupOperation.newLookup()
    .from("tags")
    .localField("tags")
    .foreignField("_id")
    .as("materialTags");
//I also want to add group operation but unable to find the proper syntax ??. 
Aggregation aggregation = Aggregation.newAggregation(unwindOperation, 
 lookupOperation1, ??groupOperation?? );
AggregationResults<Article> resultList
    = mongoTemplate.aggregate(aggregation, "articles", Article.class);

我试图玩弄团体操作，但没有太多运气。如何根据原始查询添加组操作？

提前谢谢。

Answer 1

Spring 中的组查询语法

{
    "$group": {
      "_id": "$_id",
      "title": {"$first": "$title"},
      "materialTags": {"$push": "$materialTags"}
    }
}

是

Aggregation.group("_id").first("title").as("title").push("materialTags").as("materialTags")

最终查询

UnwindOperation unwindOperation = Aggregation.unwind("tags");
LookupOperation lookupOperation1 = LookupOperation.newLookup()
    .from("tags")
    .localField("tags")
    .foreignField("_id")
    .as("materialTags");
Aggregation aggregation = Aggregation.newAggregation(unwindOperation, 
 lookupOperation1, Aggregation.group("_id").first("title").as("title").push("materialTags").as("materialTags") );
AggregationResults<Article> resultList
    = mongoTemplate.aggregate(aggregation, "articles", Article.class);

要获取更多信息，请浏览以下参考资料

http://www.baeldung.com/spring-data-mongodb-projections-aggregations

春季数据蒙戈布集团

从MongoDb聚合查询创建春季数据聚合

https://www.javacodegeeks.com/2016/04/data-aggregation-spring-data-mongodb-spring-boot.html