How to retrieve object values with same key inside an array

Question

I'm trying to get (filter) all the objects from a document array that match the same key.

Document Schema example:

{
    ...
    country: "ES",
    aut_comms: 
    [
        ...
        {name: "Aragon", province: "Huesca"},
        {name: "Aragon", province: "Teruel"},
        {name: "Aragon", province: "Zaragoza"},
        {name: "Madrid", province: "Madrid"}
        ...
    ]
}

If it is possible, im tying to retrieve from the query only the values from the objects that match the same key. Resulting in an array composed like : ["Huesca", "Teruel", "Zaragoza"]

An Array of objects that match the filter will also do the trick:

[
    {name: "Aragon", province: "Huesca"},
    {name: "Aragon", province: "Teruel"},
    {name: "Aragon", province: "Zaragoza"}
]

Thanx

Rakshith Murukannappa · Accepted Answer · 2019-06-20 10:26:10Z

2

You will be able to get this array by first unwinding the array and then manipulating it

    db.demo.aggregate([
        {
            $unwind:"$aut_comms"
        },
        {
            $match:{"aut_comms.name":"Aragon"}
        },
        {
            $group:{
                _id:null,
                result: {$push:"$aut_comms.province"}
            }
        }
   ])

answered Jun 20, 2019 at 10:26

Rakshith Murukannappa

5898 silver badges19 bronze badges

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

1 Comment

inikulin Over a year ago

Thank u so much, this accomplishes what i needed :)))

chakwok · Accepted Answer · 2019-06-20 10:50:21Z

0

Edit

It is indeed possible to do such query and output in your expected format. You can do either $unwind or $match first. Personally, I prefer to do a $match first as it would limit the number of (unnecessary) documents generated by the $unwind operation.

db.getCollection('col').aggregate([
    {$match: {"aut_comms.name": "Aragon"}},
    {$project: {_id: 0, "aut_comms": 1}},
    {$unwind: "$aut_comms"},
    {$match: {"aut_comms.name": "Aragon"}},
    {$project: {"province": "$aut_comms.province"}},
    {$group: {
        _id: null,
        province: {$push: "$province"}
    }}
])

The output will be:

/* 1 */
{
    "_id" : null,
    "province" : [ 
        "Huesca", 
        "Teruel", 
        "Zaragoza"
    ]
}

edited Jun 20, 2019 at 10:50

answered Jun 20, 2019 at 10:21

chakwok

1,04010 silver badges24 bronze badges

4 Comments

Rakshith Murukannappa Over a year ago

This is the same as just doing a find operation and then a projection, which will not yield the array that the OP wants

inikulin Over a year ago

Tried this, but it brings me the whole aut_comms array. Still not filtering by name. Thanx 4 ur help :)

chakwok Over a year ago

@inikulin I have updated the answer to your expected format.

inikulin Over a year ago

@Andyk. Thanx mate, both of ur responses are great :)))

Collectives™ on Stack Overflow

How to retrieve object values with same key inside an array

2 Answers 2

1 Comment

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related