Moongoose aggregate $match does not match id's

Question

I want to show products by ids (56e641d4864e5b780bb992c6 and 56e65504a323ee0812e511f2) and show price after subtracted by discount if available.

I can count the final price using aggregate, but this return all document in a collection, how to make it return only the matches ids

"_id" : ObjectId("56e641d4864e5b780bb992c6"), 
"title" : "Keyboard", 
"discount" : NumberInt(10),
"price" : NumberInt(1000)

"_id" : ObjectId("56e65504a323ee0812e511f2"), 
"title" : "Mouse", 
"discount" : NumberInt(0),
"price" : NumberInt(1000)

"_id" : ObjectId("56d90714a48d2eb40cc601a5"), 
"title" : "Speaker", 
"discount" : NumberInt(10),
"price" : NumberInt(1000)

this is my query

productModel.aggregate([
        {
            $project: {
                title   : 1,
                price: {
                    $cond: {
                        if: {$gt: ["$discount", 0]}, then: {$subtract: ["$price", {$divide: [{$multiply: ["$price", "$discount"]}, 100]}]}, else: "$price"
                    }

                }
            }
        }
    ], function(err, docs){
        if (err){
            console.log(err)
        }else{
            console.log(docs)
        }
    })

and if i add this $in query, it returns empty array

productModel.aggregate([
            {
                $match: {_id: {$in: ids}}
            },
            {
                $project: {
                    title   : 1,
                    price: {
                        $cond: {
                            if: {$gt: ["$discount", 0]}, then: {$subtract: ["$price", {$divide: [{$multiply: ["$price", "$discount"]}, 100]}]}, else: "$price"
                    }

                }
            }
        }
    ], function(err, docs){
        if (err){
            console.log(err)
        }else{
            console.log(docs)
        }
    })

score 117 · Accepted Answer · answered Mar 24 '16 at 04:52

117

Your ids variable will be constructed of "strings", and not ObjectId values.

Mongoose "autocasts" string values for ObjectId into their correct type in regular queries, but this does not happen in the aggregation pipeline, as in described in issue #1399.

Instead you must do the correct casting to type manually:

ids = ids.map(function(el) { return mongoose.Types.ObjectId(el) })

Then you can use them in your pipeline stage:

{ "$match": { "_id": { "$in": ids } } }

The reason is because aggregation pipelines "typically" alter the document structure, and therefore mongoose makes no presumption that the "schema" applies to the document in any given pipeline stage.

It is arguable that the "first" pipeline stage when it is a $match stage should do this, since indeed the document is not altered. But right now this is not how it happens.

Any values that may possibly be "strings" or at least not the correct BSON type need to be manually cast in order to match.

answered Mar 24 '16 at 04:52

Blakes Seven

49,422
14
129
135

That's it, it now works. but usually i throw the id as string in findOneAndUpdate or other query, and it works fine, is the problem only happen in aggregate? – Muhammad Fasalir Rahman Mar 24 '16 at 04:59
1

@MuhammadFasalirRahman This is exactly what I answered with. A `.find()` can use the `Schema` which of course has a default type of `ObjectId` for the `_id` field. Aggregation pipelines do **not** use the `Schema`, as I actually already explained. – Blakes Seven Mar 24 '16 at 05:06
3

took me three days to get here; sigh.. I created a lamda inside my schema static method `const castUserId = (userId) => mongoose.Types.ObjectId(userId)` now i'm happy – timebandit Jun 19 '18 at 17:23
2

lol....hours wasted on this issue....Thanks for the solution – Abhishek Pankar Apr 01 '21 at 14:01
Nice work around, but any chance `$in` could be slower than exact match? – shramee May 08 '22 at 20:26

score 18 · Answer 2 · answered Apr 08 '21 at 05:14

18

In the mongoose , it work fine with find({_id:'606c1ceb362b366a841171dc'})
But while using the aggregate function we have to use the mongoose object to convert the _id as object eg.

$match: { "_id": mongoose.Types.ObjectId("606c1ceb362b366a841171dc") }

This will work fine.

answered Apr 08 '21 at 05:14

Amit Kumar

181
1
3

Awesome! Seems better than using `$in`! – shramee May 08 '22 at 19:32

score 9 · Answer 3 · answered Apr 02 '21 at 17:39

9

You can simply convert your id to

 let id = mongoose.Types.ObjectId(req.query.id);

and then match

 { $match: { _id: id } },

answered Apr 02 '21 at 17:39

Sehrish Waheed

1,230
14
17

score 3 · Answer 4 · answered Mar 15 '22 at 08:04

3

instead of:

$match: { _id: "6230415bf48824667a417d56" }

use:

$match: { _id: ObjectId("6230415bf48824667a417d56") }

answered Mar 15 '22 at 08:04

Jafar Amini

315
2
8

Hi Jafar, including where ObjectId comes from would make it easier to follow ;) Upvoted :) – shramee May 08 '22 at 20:28

score 0 · Answer 5 · answered Aug 09 '22 at 14:37

Use this

$match: { $in : [ {_id: mongoose.Types.ObjectId("56e641d4864e5b780bb992c6 ")}, {_id: mongoose.Types.ObjectId("56e65504a323ee0812e511f2")}] }

Because Mongoose autocasts string values for ObjectId into their correct type in regular queries, but this does not happen in the aggregation pipeline. So we need to define ObjectId cast in pipeline queries.

Moongoose aggregate $match does not match id's

5 Answers5

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