Using Mongo DB Aggregation With Spring Mongo Template

Using aggregation in spring mongo template is quit easy and interesting .Before going foreword let's see a example of aggregation in mongo db console client.

If have collection "messages" in mongo db where i have fields like mailboxId and unreadMessageCount and some other fields like isVisible .

Then the aggregate query for Monog DB console will be like

Console Query:

db.messages.aggregate(   [

    {

        "$match":{"mailboxId":"1","isVisible":true}

            

    },

     {

       "$group":

         {

           "_id": "$mailBoxId",

           "unReadMessagesCount": { "$sum":"$unReadMessagesCount" }

         }

     }

   ]);

     

Console Result :

/* 1 */

{

    "result" : [ 

        {

            "_id" : "1",

            "unReadMessagesCount" : 12

        }

    ],

    "ok" : 1.0000000000000000

}

Aggrigate query in mongo db give list of result objects ._id is mendatory in $group

Aggrigate in Spring Mongo Template

To get the same result using mongo template we need to create same query object in our java code and we also need a java class to parsh the result and to fetch values.

Lets say we have java class AggResultObj.java to fetch result object

public class AggResultObj{

String _id;

int unReadMessagesCount;

public String get_id() {

return _id;

}

public void set_id(String _id) {

this._id = _id;

}

public int getUnReadMessagesCount() {

return unReadMessagesCount;

}

public void setUnReadMessagesCount(int unReadMessagesCount) {

this.unReadMessagesCount = unReadMessagesCount;

}

}

Then use the following code to populate aggrgated result in form of this object. Use the following code sanippet.

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.data.mongodb.core.MongoTemplate;

import org.springframework.data.mongodb.core.aggregation.Aggregation;

import org.springframework.data.mongodb.core.aggregation.AggregationResults;

import org.springframework.data.mongodb.core.query.Criteria;

public class DummyTest {

@Autowired

MongoTemplate mongoTemplate;

public void test() {

Aggregation agg = Aggregation.newAggregation(

Aggregation.match( Criteria.where("mailBoxId").is("1").and("isVisible").is(false)), Aggregation.group("$mailBoxId").sum("$unReadMessagesCount").as("unReadMessagesCount")

);

System.out.println("Query ==>>["+agg.toString()+"]");

AggregationResults<AggResultObj> data = mongoTemplate.aggregate(agg, "messages", AggResultObj.class);

System.out.println("UnReadMesasgeCode :"+data.getUniqueMappedResult().getUnReadMessagesCount());

}

}