mongodb - Spring Data MongoDB聚合场景

Question

如何翻译

$group : {
   _id :  1 ,
    likes    : { $avg: { $size: ["$likes"] }},
    count:   { $sum: 1 },
 }

进入 spring-data-mongodb 聚合查询？

Answer 1

您可以使用以下代码:

ArrayList<String> list = new ArrayList<>();
list.add("$likes");

BasicDBObject idObj = new BasicDBObject("_id", 1);
BasicDBObject likesObj = new BasicDBObject("$avg", new BasicDBObject("$size", list));
BasicDBObject countObj = new BasicDBObject("$sum", 1);

idObj.append("likes", likesObj).append("count", countObj);
BasicDBObject group = new BasicDBObject("$group", idObj);


List<DBObject> pipeline = new ArrayList<>();
pipeline.add(group);

MongoTemplate mongoTemplate = new MongoTemplate(new MongoClient(), "dbname");
AggregationOutput aggregationOutput = mongoTemplate.getCollection("collectionName")
        .aggregate(pipeline);
List<DBObject> dbObjects = (List<DBObject>) aggregationOutput.results();

//convert dbObjects into appropriate output