How to select only an element of an array within a Mongoose.find

Question

Let's say I've got these values in database:

{
    name: '1',
    values: [{
        subname: 'awesome'
    }, {
        surname: 'cool'
    }]
}

how could I filter the array with only the value I'm interested in?

I would like to get as result of my find:

{
    name: '1',
    values: [{
        subname: 'awesome'
    }]
}

I thought maybe there is a possibility with select? Something like

MyCollection.find({name: '1'}).select(BLACK_MAGIC);

Where BLACK_MAGIC filters my array with the values I'm interested in, in this example values.subname = 'awesome'

Thx in advance for any ideas

Side note: I'm interesting to solve this with Mongoose queries and functions, not a solution with a post javascript on the resulting array

Thx @Mikey, look like you are right, the examples of the documentation seems to fit my needs...gonna study and try that! — David Dal Busco
– David Dal Busco, Commented Jul 10, 2017 at 18:25
@Mikey it kind of work but doesn't fulfill 100% what I'm looking for. Doing Collection.find({something}, {$elementMatch}) gonna return {_id, theElementMatched} but I would like to return {_id, everything else, theElementMatched} — David Dal Busco
– David Dal Busco, Commented Jul 10, 2017 at 18:46

Mikey · Accepted Answer · 2017-07-10 23:19:14Z

2

I think you could use aggregation for this.

You would $unwind so that each values object is in a separate document.

Then filter the results with $match.

MyCollection.aggregate([
    {
        $unwind: '$values'
    },
    {
        $match: { 
            'values.subname': 'awesome'
        }
    },
    // EDIT
    {
        $group: {
            _id: '$_id',
            name: { 
                $first: "$name"
            },
            values: {
                $push: { subname: "$values.subname" }
            }
         }
    }
], function (err, results) {

});

If it works, you are little bit closer. The only thing is that values is an object, not an array of one object. You could probably use $group with $first to get desired result.

edited Jul 10, 2017 at 23:19

answered Jul 10, 2017 at 20:16

Mikey

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1 Comment

David Dal Busco Over a year ago

cool thx for the answer. aggregation and unwind as you described did the job!

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