How to acces object in nested arrays in mongo db

Question

Assuming the following a portfolio collection:

{
    "_id" : ObjectId("50e5a858ad06fe3439000001"),
    "name" : "Portfolio 1",
    "description" : "description Portfolio 1",
    "userId" : "",
    "wallets" : [ ]
}
{
    "_id" : ObjectId("50e5a858ad06fe3439000002"),
    "name" : "Portfolio 2",
    "description" : "description Portfolio 2",
    "userId" : "",
    "wallets" : [
        {
            "_id" : ObjectId("50e5ac69f214a46139000001"),
            "name" : "wallet name 2-1",
            "description" : "description du wallet",
        "cards" : [
            {
                "_id" : ObjectId("50ebe4b5906a1e830d000001"),
                "name" : "Card 2-1-1",
                "description" : "description card 1",
            },
            {
                "_id" : ObjectId("50ebe61f2c0f189310000001"),
                "name" : "Card 2-1-2",
                "description" : "description de la carte",
            },
            {
                "_id" : ObjectId("50ebe6202c0f189310000002"),
                "name" : "Card 2-1-2",
                "description" : "description de la carte",
            },
            {
                "_id" : ObjectId("50ebe6212c0f189310000003"),
                "name" : "Card 2-1-3",
                "description" : "description de la carte",
            },
            {
                "_id" : ObjectId("50ebe6212c0f189310000004"),
                "name" : "Card 2-1-4",
                "description" : "description de la carte",
            }
        ]
    },
    {
        "_id" : ObjectId("50ebe6b22c0f189310000005"),
        "name" : "wallet 2-2",
        "description" : "",
        "cards" : [
            {
                "_id" : ObjectId("50ec21063f3c5f9f12000001"),
                "name" : "Card 2-2-1",
                "description" : "",
            }
        ]
    },
    {
        "_id" : ObjectId("50ebe6ba2c0f189310000006"),
        "name" : "wallet 2-3",
        "description" : "",
        "cards" : [
            {
                "_id" : ObjectId("50ec21233f3c5f9f12000002"),
                "name" : "Card 2-3-1",
                "description" : "",
            }
        ]
    }
]
}

I would like to access a specific card thanks to portfolio,wallet and card _id. What I'd like to have is:

{
"_id" : ObjectId("50e5a858ad06fe3439000002"),
"wallets" : [
    {
        "_id" : ObjectId("50e5ac69f214a46139000001"),
        "cards" : [
            {
                "_id" : ObjectId("50ebe4b5906a1e830d000001"),
                "name" : "Card 2-1-1",
                "description" : "description card 1",
            }
        ]
    },
]

}

I'm working on mongodb 2.2.2 on nodejs/mongo-native-driver.

Any help will be appreciate (shell example or javascript appreciated)

Thanck you.

mjhm · Accepted Answer · 2013-01-08 19:23:38Z

3

Similar to slee's answer using the Aggregation Framework, though it's better to cull entries out of the results early to prevent unnecessary unwinding.

    var aggOps = [
        { $match: {
            _id: portfolioID
        }},
        {$unwind: '$wallets'},
        { $match: {
            'wallets._id': walletID
        }},
        {$unwind: '$wallets.cards'},
        { $match: {
            'wallets.cards._id': cardID
        }},
    ];

    collection.aggregate(aggOps, function (err, result) {
        console.log(result);
    });

answered Jan 8, 2013 at 19:23

mjhm

16.8k10 gold badges47 silver badges56 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

slee Over a year ago

Yup, mjhm's right. It's definitely better to put $match earlier in the pipeline to reduce the number of documents being operated upon later in the pipeline.

slee · Accepted Answer · 2013-01-08 15:45:04Z

1

The Aggregation Framework can be used. Specifically, the $unwind operator is probably most useful in this case. Bear in mind that $unwind won't expand empty arrays, so the first document in your example is excluded from the aggregation pipeline.

db.collection.aggregate(
    { $unwind : "$wallets" },
    { $unwind : "$wallets.cards" },
    { $match: {
        "_id"               : ObjectId("50e5a858ad06fe3439000002"),
        "wallets._id"       : ObjectId("50e5ac69f214a46139000001"),
        "wallets.cards._id" : ObjectId("50ebe4b5906a1e830d000001")
    } }
)

answered Jan 8, 2013 at 15:45

slee

5342 silver badges6 bronze badges

Comments

cubbuk · Accepted Answer · 2013-01-08 16:18:28Z

1

http://docs.mongodb.org/manual/reference/projection/elemMatch/

According to the mongodb documents this can be done by $elemMatch operator. I tried to come up with the query, can you check if it works for your case or you can modify according to your needs.

var projection = { _id: 1, wallets: { _id: 'walletId', $elemMatch: { cards._id: 'cardId'}}};

db.portfolio.find(    {_id: 'portfolio_id'},    projection )

edited Jan 8, 2013 at 16:18

answered Jan 8, 2013 at 15:41

cubbuk

7,9284 gold badges39 silver badges64 bronze badges

2 Comments

mjhm Over a year ago

$elemMatch works for projecting the correct wallet item, but it doesn't seem to work for the nested cards array.

cubbuk Over a year ago

Can you try: db.portfolio.find( {_id: 'portfolio_id', "wallets._id" : 'walletId'}, projection ). Not sure of exact syntax for the query.

Collectives™ on Stack Overflow

How to acces object in nested arrays in mongo db

3 Answers 3

1 Comment

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related