Mongo and Java read nested documents values

Question

My mongo collections contains following documents

{

"syslog": [
    {
        "alertId": "N/A",
        "time": "06:46:57",
        "device": "10.10.20.1"
    },
    {
        "alertId": "N/A",
        "time": "06:47:30",
        "device": "10.10.20.2"
    }
]
}

now I want to read only values of given device.

Suppose if I set device="10.10.20.2" it will shows only "alertId": "N/A", "time": "06:47:30", "device": "10.10.20.2" for this I write java code as below

BasicDBObject criteria = new BasicDBObject();                                       

criteria.put("syslog.device","10.10.20.2");
DBCursor cur = coll.find(criteria);
while(cur.hasNext() && !isStopped()) {
    String json = cur.next().toString(); 
}//end of while

When I print json it shows me whole json values. How I should find only selected values of given device?

What do you mean with When I print json it shows me whole json values ? — Konstantin Yovkov
– Konstantin Yovkov, Commented Jan 29, 2014 at 12:43
dont print the whole JSON, pick the fields you want before you convert it to string — Sleiman Jneidi
– Sleiman Jneidi, Commented Jan 29, 2014 at 12:46

Parvin Gasimzade · Accepted Answer · 2014-01-29 12:46:40Z

3

You should use $elemMatch operator to project array fields. You should update your query as follows :

db.collection.find({"syslog.device" : "10.10.20.2"},{syslog : {$elemMatch : {device : "10.10.20.2"}}})

In Java :

BasicDBObject criteria = new BasicDBObject();                                       
criteria.put("syslog.device","10.10.20.2");

BasicDBObject elemMatchObj = new BasicDBObject();
elemMatchObj.put("$elemMatch", new BasicDBObject("device", "10.10.20.2"));

DBCursor cur = coll.find(criteria, new BasicDBObject("syslog", elemMatchObj));
while(cur.hasNext() && !isStopped()) {
    String json = cur.next().toString(); 
}//end of while

answered Jan 29, 2014 at 12:46

Parvin Gasimzade

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