MongoDB : How to make a Query within Array Structured Collection .

Question

I have a Mongo DB COllection as shown

{
    "name": "SAM",
    "collection": [
        {
            "date": "2013-03-16",
            "values": [
                {
                    "price": "24.0"
                }
            ]
        },
        {
            "date": "2013-04-20",
            "values": [
                {
                    "price": "10.0"
                }
            ]
        },
        {
            "date": "2013-05-18",
            "values": [
                {
                    "price": "12.0"
                }
            ]
        },
        {
            "date": "2013-06-22",
            "values": [
                {
                    "price": "10.0"
                }
            ]
        },
        {
            "date": "2013-09-21",
            "values": [
                {
                    "price": "38.0"
                }
            ]
        }
    ]
}

I was trying to get data related to a Particular date (2013-03-16) as shown But i am getting data of all the dates .

This is what i tried .

Please tell me where i am doing mistake .

package com;

import java.net.UnknownHostException;

import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.Mongo;

public class Test {

    public static void main(String args[]) throws UnknownHostException {
        Mongo mongo = new Mongo();
        DB db = mongo.getDB("test");
        DBCollection mycollection = db.getCollection("mycollection");

        BasicDBObject query = new BasicDBObject();
        query.put("name", "SAM");
        query.put("collection.date", "2013-03-16");

        DBCursor cursor = mycollection.find(query);

        while (cursor.hasNext()) {
            System.out.println(cursor.next());
        }

    }

}

MongoDB will return the entire record not a subset of a record when queried. Your "collection" above looks to be a single record. You could try breaking this up into individual records, each with name, date and values. — James Wahlin
– James Wahlin, Commented Mar 1, 2013 at 19:37
If you need to use the embedded array for your schema, you can use the $unwind operator from the Aggregation Framework to break up the single document into a document per entry in the embedded array. — slee
– slee, Commented Mar 1, 2013 at 19:41
Thanks for the response , but i cannot change the Structure of Database . So you mean to say that it is not possible to avoid entire record from returning. — Pawan
– Pawan, Commented Mar 1, 2013 at 19:45

JohnnyHK · Accepted Answer · 2013-03-01 20:01:27Z

1

You can use the $ positional projection operator to do this in the field selection parameter of find:

BasicDBObject query = new BasicDBObject();
query.put("name", "SAM");
query.put("collection.date", "2013-03-16");
BasicDBObject fields = new BasicDBObject();
fields.put("name", 1);
fields.put("collection.$", 1);

DBCursor cursor = mycollection.find(query, fields);

edited Mar 1, 2013 at 20:01

answered Mar 1, 2013 at 19:52

JohnnyHK

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3 Comments

Pawan Over a year ago

This is working , but could you please tell me why you have hardcoded 1 for name and collection keys ??

JohnnyHK Over a year ago

@PreethiJain Because the value of the keys in the field selection parameter is determines whether the field is included in the result; 1 (or any truthy value) for included, 0 for excluded.

Pawan Over a year ago

what i understood is that the fileds name and collection.$ will be part of result ?? Am i right . please tell me

vikasing · Accepted Answer · 2013-03-01 19:45:33Z

0

You are trying to query an element inside the array collection, you need to use $elemMatch, instead of,

query.put("collection.date", "2013-03-16");

you can try with

query.put("collection", new BasicDBObject("$elemMatch", new BasicDBObject("date","2013-03-16")));

Read more about it here: http://docs.mongodb.org/manual/reference/projection/elemMatch/

answered Mar 1, 2013 at 19:45

vikasing

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2 Comments

Pawan Over a year ago

Thanks Vikas, i tried but still i am getting all the Dates as response .

vikasing Over a year ago

As JohnnyHK mentioned in his code, you also need to pass new BasicDBObject("collection.$", 1); in the find method to get a particular entry, here is the doc for $ operator: docs.mongodb.org/manual/reference/projection/positional/#_S_

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