Insert a document into another document in MongoDB

Question

I'm trying to add a document in another document.

I am trying to insert a new document with a timestamp as a key and light prox and temp as the content of that document into document sensor_collection.

It's logical that my code doesn't work, because I'm setting a new sensor_collection. Does anyone know how I can set a timestamp document in sensor_collection or is it adviced not to do it this way?

This is the code:

MongoCollection<Document> collection  =  db.getCollection(Sensor.KEY_COLLECTION);
    //append sensor data to existing document
    collection.updateOne(doc, new Document("$set",
            new Document("sensor_collection", new Document(
                    String.valueOf(stamp.getCurrentTime()), new Document(
                            Sensor.KEY_LIGHT, sensorData.getLight())
                            .append(Sensor.KEY_PROX, sensorData.getProx())
                            .append(Sensor.KEY_TEMP, sensorData.getTemp())
                    ))));

Currently this code overrides the timestamp that's already in the db.

I'm kinda lost. do you want to append your new doc to existing set? — Ali Dehghani, Dec 19 '15 at 16:31
Hey, in sensor_collection I want to have multiple timestamps each containing light, prox and temp. And I want to add another timestamp object to sensor_collection. — Martijn Jan Jaap de Bruin, Dec 19 '15 at 18:11

score 1 · Answer 1 · answered Dec 19 '15 at 16:51

1

If you want to append to an existing embedded collection, use $push instead of $set. The $push operator appends a specified value to an array. Something like this:

collection.updateOne(doc, new Document("$push",
            new Document("sensor_collection", new Document(
                    String.valueOf(stamp.getCurrentTime()), new Document(
                            Sensor.KEY_LIGHT, sensorData.getLight())
                            .append(Sensor.KEY_PROX, sensorData.getProx())
                            .append(Sensor.KEY_TEMP, sensorData.getTemp())
                    ))));

For more details on mongo's update operators, check this out

answered Dec 19 '15 at 16:51

Ali Dehghani

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Hey, thanks for your answer. $push works if sensor_collection was an array. It's an object. Is it still possible to add another timestamp object to sensor_collection? Without using array's. Or is using arrays the more common approach? – Martijn Jan Jaap de Bruin Dec 19 '15 at 18:16
You could select the embedded collection instead of whole collection and just update that. may be this works but using an array would be simpler i guess – Ali Dehghani Dec 19 '15 at 18:44

score 0 · Accepted Answer · edited Dec 22 '15 at 19:29

In the Mongodb documentation I found this:

"To specify a <field> in an embedded document or in an array, use dot notation."

I used the $set operator. And I'm setting sensor_collection.timestamp

MongoCollection<Document> collection  =  db.getCollection(Sensor.KEY_COLLECTION);
    //append sensor data to existing document
    collection.updateOne(doc, new Document("$set",
            new Document("sensor_collection."+String.valueOf(stamp.getCurrentTime()),
                     new Document(
                            Sensor.KEY_LIGHT, sensorData.getLight())
                            .append(Sensor.KEY_PROX, sensorData.getProx())
                            .append(Sensor.KEY_TEMP, sensorData.getTemp())
                    )));

This works. Gives:

Insert a document into another document in MongoDB

2 Answers2