CODEWITHSUNDEEP
node.jsmongodb
Rahmani Seif
Rahmani Seif

Reputation: 69

Find document then get all related documents

I have this mongodb document : 

{
    "_id" : ObjectId("5e382d27bb4bd5ce3ef5fb1d"),
    "code" : "25116",
    "datecrea" : "2015-11-14 18:23:24",
    "datemodif" : "2015-11-14 18:23:24",
    "datas" : {
        "songId" : 25116,
        "artistId" : 128,
        "albumId" : 1822,
        "name" : "Free Me",
        "songTrack" : 10,
        "genres" : [ 
            "24"
        ],
    }
}

I want to make a request that search for the song by its genre which is an array of genres, and then get me the artist and the album related to this song based on the datas.artistId and datas.albumId fields.

I have tried this query : 

db.getCollection('songs').aggregate([
{ $elemMatch: { "datas.genre": 31 } },
{ $lookup: { from: "artists", localField: "datas.artisId", foreignField: "code", as: "artist" } },
{ $unwind: "$artist"}
])

But it returns an error, knowing that I totally news to mongodb. Thanks to everyone for helping

Upvotes: 1

Views: 38

Answers (1)

Tom Slabbaert
Tom Slabbaert

Reputation: 22316

You are not far off. You just have two minor syntax errors.

  1. The $elemMatch, Without going too much into it. $elemMatch is not a pipeline stage and cannot be used in an aggregate operation. it is typically used in a find query.

  2. In the lookup you wrote datas.artisId instead of datas.artistId

So change you're pipeline into this:


db.getCollection('songs').aggregate([
    { $match: { "datas.genre": 31 } },
    { $lookup: { from: "artists", localField: "datas.artistId", foreignField: "code", as: "artist" } },
    { $unwind: "$artist"}
])

One more fun fact, unrelated to the actual code, the word data is already in it's plural form. hence datas is a grammatical mistake. And in case you're wondering the singular form of data is datum.

Upvotes: 1

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