how to get this query form nested array with findOne in mongoDB

Question

i have this collection in mongodb :

db.persons.find().pretty();{
"_id" : ObjectId("564635a944ae32e021f8b81b"),
"items" : [
        {
                "_id" : ObjectId("564635a944ae32e021f8b819"),
                "personId" : 1,
                "first_name" : "A",
                "last_name" : "B",
                "gender" : "m",
                "comment" : "123"
        },
        {
                "_id" : ObjectId("564635a944ae32e021f8b81a"),
                "personId" : 2,
                "first_name" : "w",
                "last_name" : "X",
                "gender" : "m",
                "comment" : "987"
        }
]},{
"_id" : ObjectId("564635a944ae32e021f8b812"),
"items" : [
        {
                "_id" : ObjectId("564635a944ae32e021f8b8d5"),
                "personId" : 3,
                "first_name" : "Y",
                "last_name" : "Z",
                "gender" : "f",
                "comment" : "357"
        }]}

with this command(findOne) :

> db.persons.findOne({"items.personId" : 1})

get this result :

{
"_id" : ObjectId("564635a944ae32e021f8b81b"),
"items" : [
        {
                "_id" : ObjectId("564635a944ae32e021f8b819"),
                "personId" : 1,
                "first_name" : "A",
                "last_name" : "B",
                "gender" : "m",
                "comment" : "123"
        },
        {
                "_id" : ObjectId("564635a944ae32e021f8b81a"),
                "personId" : 2,
                "first_name" : "w",
                "last_name" : "X",
                "gender" : "m",
                "comment" : "987"
        }
]}

but; how I get this result : only first_name & last_name & _id from items that personId = 1

        {                    
                "_id" : ObjectId("564635a944ae32e021f8b819"),
                "first_name" : "A",
                "last_name" : "B"
        }

(just with the findOne command(No aggregate)). very thanks...

chridam · Accepted Answer · 2015-11-17 13:24:52Z

1

Best you use a combination of the positional $ operator in your projection to return just the items array, use the native JavaScript's map() method to customize the return items array returned for it to have just the fields you want and then since there would be only one array element returned, your final result is obtained by the 0 index position. The following query explains the above:

var item = db.persons.findOne({"items.personId": 1}, {"items.$": 1, "_id": 0}).items.map(function (item){ 
    return { 
        _id: item._id, 
        first_name: item.first_name,
        last_name: item.last_name
    } 
})[0];
printjson(item);

Output:

{
    "_id" : ObjectId("564635a944ae32e021f8b819"),
    "first_name" : "A",
    "last_name" : "B"
}

answered Nov 17, 2015 at 13:24

chridam

104k26 gold badges246 silver badges243 bronze badges

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

1 Comment

Abdullah Rasheed Over a year ago

Nice. you beat me to it!

Community · Accepted Answer · 2017-05-23 11:59:02Z

1

Have a look at: MongoDB get SubDocument. In short: What you want seems to be impossible. You get something similar with aggergation. The best you can do without aggregation would be:

db.persons.findOne({"items.personId" : 1}, {"items.$", "_id":0})

which would return

{
    "items" : [
        {
            "_id" : ObjectId("564635a944ae32e021f8b819"),
            "first_name" : "A",
            "last_name" : "B"
        }
    ]
}

edited May 23, 2017 at 11:59

CommunityBot

11 silver badge

answered Nov 17, 2015 at 13:11

tadumtada

1741 gold badge2 silver badges10 bronze badges

1 Comment

Mostafa Ghasemi Over a year ago

Hi thanks, this command return all. i want just first_name, last_name and _id of items. and you edit "items.$" to "items.$" : 1

Collectives™ on Stack Overflow

how to get this query form nested array with findOne in mongoDB

2 Answers 2

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related