Get back matched array elements present in a document's field which is also an array

Question

I have an array defined below which contains some strings,

arr = ["hola", "hii", "hey", "namaste"];

Now below are the documents i have in mongodb

{
    "user_id": "Michael",
    "list": ["hola", "ola", "hey", "maybe"]
}

Now i want to write a query in mongodb which returns all "arr" elements which are also present in "list" of the particular "user_id".

So My Desired Output is

_id: "_id" : ObjectId("5828ae4779f2e01b06bb7a61"), results: ["hola", "hey"]

i wrote below query using aggregation but i am getting error as

MongoError: FieldPath field names may not start with '$'

My code

arraymodel.aggregate(
        { $match: { user_id: "Michael" }},
        { $unwind: '$list'},
        { $match: {list: {$in: arr}}},
        { $group: {_id: '$_id', results: {$push: '$list.$'}}},
        function(err, docs) {
            if (err) {
                console.log('Error Finding query results');
                console.log(err);
            } else {
                if (docs) {
                    console.log('docs: ', docs);
                } else {
                    console.log('No Arr Found');
                }
            }
        }
        );

score 2 · Answer 1 · answered Nov 16 '16 at 14:15

2

simply get rid of the $ in {$push: '$list.$'} and you will get the desired output.

below is the complete query :

    db.collection.aggregate(
{$match:{user_id:"Michael"}},
{$unwind:'$list'},
{$match:{list:{$in:["hola","hey"]}}},
{$group:{_id:"$_id",results:{$push:"$list"}}})

answered Nov 16 '16 at 14:15

satish chennupati

2,602
1
18
27

Can you please help me out i have another question on aggregation here http://stackoverflow.com/questions/40596317/use-aggregation-in-mongodb-to-perform-update-after-query-matches/40613866#40613866. – Prakash Kumar Nov 16 '16 at 16:04
very nice answer but since Veerma posted answer first i am accepting his answer – Prakash Kumar Nov 16 '16 at 16:06
sure let me go through that – satish chennupati Nov 16 '16 at 16:35
did you get anything ?? – Prakash Kumar Nov 17 '16 at 21:11
http://stackoverflow.com/questions/41042482/change-type-of-field-inside-mongodb-aggregation-and-does-lookup-utilises-index – Prakash Kumar Dec 08 '16 at 15:11

score 1 · Accepted Answer · answered Nov 16 '16 at 14:10

1

You can try $setIntersection for this.

db.arrayModel.aggregate(
    [{
        $match: {
            user_id: "Michael"
        }
    }, {
        $project: {
            _id: 1,
            results: {
                $setIntersection: ["$list", ["hola", "hii", "hey", "namaste"]]
            }
        }
    }]
)

Sample Output

{ "_id" : ObjectId("582c6902a5ff9d6d50e722c3"), "results" : [ "hola", "hey" ] }

answered Nov 16 '16 at 14:10

s7vr

73,656
11
106
127

sorry as satish posted answer first i am accepting it. – Prakash Kumar Nov 16 '16 at 16:02
Also can you please help me out i have another question on aggregation here http://stackoverflow.com/questions/40596317/use-aggregation-in-mongodb-to-perform-update-after-query-matches/40613866#40613866. – Prakash Kumar Nov 16 '16 at 16:03
just an fyi I posted the answer first. – s7vr Nov 16 '16 at 16:03
sorry posts were sorted according to active i accepted now thanks a lot :) – Prakash Kumar Nov 16 '16 at 16:05
did you get anything ?? about the question i asked above ?? – Prakash Kumar Nov 17 '16 at 21:11
http://stackoverflow.com/questions/41042482/change-type-of-field-inside-mongodb-aggregation-and-does-lookup-utilises-index – Prakash Kumar Dec 08 '16 at 15:11

Get back matched array elements present in a document's field which is also an array

2 Answers2