lookup on ObjectId's in an array

Question

I have shops collection and user collection with list of shops ids inside of it as strings.

example of shop document:

    {
            "_id" : ObjectId("5a0c6797fd3eb67969316ce2"),
            "picture" : "http://placehold.it/150x150",
            "name" : "Genmom",
            "email" : "[email protected]",
            "city" : "Rabat",
            "location" : {
                    "type" : "Point",
                    "coordinates" : [
                            -6.79387,
                            33.83957
                    ]
            }
    }

example of user collection:

{
            "_id" : ObjectId("5c04b943ff491824b806686a"),
            "email" : "[email protected]",
            "password" : "$2a$10$4Wt5Rn6udxREdXCIt3hGb.sKhKUKOlyiYKmLTjYG3SqEPKFSw9phq",
            "likedShops" : [
                    "5a0c6797fd3eb67969316ce2",
                    "5c07ada8ff49183284e509d1",
                    "5c07acc1ff49183284e509d0"
            ],
            "dislikedShops" : [ ]
}

I want to return the detail of the likedShops.

What is the type of likedShops ids? String or OBjectID? And what version of mongo you are using? — Ashh
– Ashh, Commented Dec 5, 2018 at 16:38

Ashh · Accepted Answer · 2018-12-05 16:53:37Z

5

You can use below $lookup aggregation

db.users.aggregate([
  { "$lookup": {
    "from": "shops",
    "let": { "likedShops": "$likedShops" },
    "pipeline": [
      { "$match": { "$expr": { "$in": ["$_id", "$$likedShops"] }}}
    ],
    "as": "likedShops"
  }}
])

Or if your ids are string then use $toString aggregation with the ObjectIds

db.users.aggregate([
  { "$lookup": {
    "from": "shops",
    "let": { "likedShops": "$likedShops" },
    "pipeline": [
      { "$match": { "$expr": { "$in": [{ "$toString": "$_id" }, "$$likedShops"] }}}
    ],
    "as": "likedShops"
  }}
])

edited Dec 5, 2018 at 16:53

answered Dec 5, 2018 at 16:43

Ashh

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3 Comments

Ayoub k Over a year ago

I'm getting "errmsg" : "$in requires an array as a second argument, found: missing"

Ayoub k Over a year ago

by the way i have some users without likedShops field:)

Ashh Over a year ago

Your some of the documents doesn't contain the likedShop field. See this

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