Retrieve Sub Document in Mongo

Question

I'm new to Mongo and struggling to retrieve a specific Sub Document of a specific Document

Given the following collection, I want to retrieve the content where "id" = 1 and "data.id" = 2. So, I'd want my result to be the "Java" object.

{
    "id" : "1",
    "title" : "Section1",
    "data" : [ 
        {
            "id" : "1",
            "Product" : "Scala",
            "Description" : "",
        }, 
        {
            "id" : "2",
            "Product" : "Java",
            "Description" : "",
        }, 
        {
            "id" : "3",
            "Product" : "Ruby",
            "Description" : "",
        }, 
        {
            "id" : "4",
            "Product" : "HTML5",
            "Description" : "",
        }
        ]
}

{
    "id" : "2",
    "title" : "Section2",
    "data" : [ 
        {
            "id" : "4",
            "Product" : "Ansible",
            "Description" : "a free software platform for configuring and managing computers",
        }, 
        {
            "id" : "1",
            "Product" : "Chef",
            "Description" : "an open source configuration management tool",
        }, 
        {
            "id" : "2",
            "Product" : "Puppet",
            "Description" : "an open-source tool for managing the configuration of computer systems",
        }, 
        {
            "id" : "3",
            "Product" : "Saltstack",
            "Description" : "open source configuration management and remote execution application",
        }
   ]
}

I'm executing a query like db.myCollection.find({$and : [{"id":"1"},{"data.id":"2"}]}) but this returns the whole document with an id of "1" rather than just the subdocument I'm interested in.

Am I asking Mongo to do something that it's not designed for, or is it just my syntax that is at fault?

To do that, you are going to need to use projections. you can find some examples here: https://docs.mongodb.org/v3.0/reference/operator/aggregation/project/ — jpgrassi, Dec 15 '15 at 10:58
Possible duplicate of [Retrieve only the queried element in an object array in MongoDB collection](http://stackoverflow.com/questions/3985214/retrieve-only-the-queried-element-in-an-object-array-in-mongodb-collection) — styvane, Dec 15 '15 at 14:29

score 3 · Accepted Answer · answered Dec 15 '15 at 11:01

3

Maybe this will help:

db.myCollection.find({"id":"1","data.id":"2"},{"id":1,"data.$":1})

Its not required to pass $and

answered Dec 15 '15 at 11:01

Sarath Nair

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What does that `$` mean? Thanks! – Minh Nghĩa Aug 08 '19 at 03:18
1

It would return the matching subdocument found in `data` instead of returning the whole `data` array – Sarath Nair Aug 19 '19 at 08:58

score 2 · Answer 2 · answered Dec 15 '15 at 11:26

2

You can use $match in conjunction with $unwind. These two are a part of aggregation framework.

The answer to your question is :

db.collection.aggregate([{$unwind:'$data'},{$match:{'data.Product':{$eq:'Java'}}}]);

Refer: MongoDb unwind operator

answered Dec 15 '15 at 11:26

harshavmb

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hecnabae · Answer 3 · 2015-12-15T11:59:42.137

You can use aggregation framework.

Retrieve document with matching "data" item.

db.getCollection('yourColl').aggregate([ {$unwind:"$data"}, {$match:{"id":"1", "data.id":"2"}}, {$group:{_id:"$_id", "id":{$first:"$id"}, "title":{$first:"$title"}, "data":{$push:"$data"}}} ])
If you only want get specific subdocument

db.getCollection('yourColl').aggregate([ {$unwind:"$data"}, {$match:{"id":"1", "data.id":"2"}}, {$project:{_id:0, "id":"$data.id", "product":"$data.Product", "Description":"$data.Description"}} ])

score 0 · Answer 4 · answered Dec 15 '15 at 11:00

0

Answered my own question :

db.myCollection.find({$and : [{"id":"1"},{"data.id":"2"}]},{"data.$":1})

answered Dec 15 '15 at 11:00

DaveH

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Retrieve Sub Document in Mongo

4 Answers4