Filter array elements by nested array of objects

Question

First, let me say that this question is slightly different to others I've seen regarding nested arrays in mongo.

Most of them ask how to get a specific element in a nested array. I want to get all elements of an array that has itself another array containing a given value.

I have documents, that look like this:

{
    _id: something,
    value: something,
    items: [{ 
        name: someItem,
        price: somePrice,
        stores:[
            {name: storeName, url: someUrl },
            {name: anotherStoreName, url: someOtherUrl}
        ]
    },
    {
        name: someOtherItem,
        price: someOtherPrice,
        stores:[
            {name: storeName, url: someUrl },
            {name: yetAnotherStoreName, url: someOtherUrl}
        ]
    }]
}

What I want is to get only the items elements that have a given store in the stores array. This is, if I ask storeName, I should get both items in the example. But if I ask for anotherStoreName, I should only get the first element of the array items.

Searching for similar questions and trying the solutions I can only get the first matching element of items, but I want all the matching elements.

I'd appreciate any help.

Can you show us the expected result?

Sede
– Sede

2015-06-30 23:01:07 +00:00
Commented Jun 30, 2015 at 23:01 — Sede
– Sede, Commented Jun 30, 2015 at 23:01

Vishwas · Accepted Answer · 2015-07-01 05:09:29Z

1

You should use mongo aggregation to get result in following way.

First use $unwind to separate array of items and then add match condition.

db.collection.aggregate([{
    $unwind: "$items"
}, {
    $match: {
    "items.stores.name": "storeName"
    }
}, {
    $project: {
    _id: 0,
    items: "$items"  //you can add multiple fields here
    }
}]);

answered Jul 1, 2015 at 5:09

Vishwas

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Comments

Miguel Lattuada · Accepted Answer · 2015-06-30 23:11:14Z

0

You should use the aggregation framework to unwind elements on the items array and then treat them as individual documents.

db.data.aggregate([
    {
        $unwind: "$items"
    },
    {
        $project: {
            _id: 0,
            items: "$items"
        }
    },
    {
        $match: {
            "items.stores.name": "yetAnotherStoreName"
        }
    }
]);

$project just let you work with the important part of the document.
This works on the mongoshell be carefully when using your driver.

The result.

Result image

answered Jun 30, 2015 at 23:11

Miguel Lattuada

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