Spring data mongodb aggregation scenario - mongodb

Question

How can I translate
$group : {
_id : 1 ,
likes : { $avg: { $size: ["$likes"] }},
count: { $sum: 1 },
}
into a spring-data-mongodb aggregation query?

Answer 1

You can use Following Code :
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

Answer 2

You can use also following way for spring data mongodb
List<AggregationOperation> stages = new ArrayList<>();
GroupOperation groupOperation = group()
.count().as("count")
.avg(ArrayOperators.Size.lengthOfArray("likes")).as("likes");
stages.add(groupOperation);
AggregationResults<ResultDTO> result = mongoOperation.aggregate(newAggregation(stages),
"collectionName", ResultDTO.class);
public class ResultDTO {
private Integer count;
private Double likes;
//getter setter
}