Mongoose: Using $elemMatch to filter a subdocument array generates error [Error: Can't use $elemMatch with ObjectId.]

[valerianrossigneux]

Hi, I want to get all the "activities" on the "sites" that are managed by a specific user so, I've tried to query activities with the following:

            site: {
                $elemMatch: {
                    managers: { // managers is an array of ObjectId
                        $in: [req.user._id] // this is an ObjectId
                    }
                }
            }

I'm getting the error [Error: Can't use $elemMatch with ObjectId.]
Can't find much on that error on internet...
Thanks!

[vkarpov15]

If managers is an array of ObjectId, you should just use:

Sites.find({ managers: { $in: [req.user._id] } }, callback);

You could also use the below, but not recommended because $elemMatch is only necessary if you need to match arrays of subdocs by multiple criteria.

m.findOne({
  ids: {
    $elemMatch: {
      $in: [new mongoose.Types.ObjectId('000000000000000000000001')] 
    }
  }
}, function() {});

The query you specified will assume that site is an array which contains subdocs with a "manager" key that's an _id.

[valerianrossigneux]

Actually I'm not looking for "activities" (not site) where the user logged in is a "manager" of the "site" this activity belongs to. I want to filter the results for specific sub document value.

activity:
    site: ObjectId

site:
    managers: [ObjectId]

[vkarpov15]

You can just use $in here, $elemmatch is redundant here because managers isn't an array of subdocs

[valerianrossigneux]

I apologize for wasting your time, but I really can't figure out the solution. I tried to go straight as you said:

Mongoose: activities.find({ 'site.managers': { '$in': [ ObjectId("521bd88c08b986f811000001") ] }, delete: false }) { fields: { delete: 0, updated_at: 0, created_at: 0, deleted_at: 0 } }

But this query doesn't return the activities for which the the populated site is managed by the user passed in the query.... it always return empty results.

[vkarpov15]

Hmm that's strange. 2 things you can do to give me some more insight:

1) Does this query work in the mongodb shell? That is, can you do db.activities.find({ 'site.managers': { '$in': [ ObjectId("521bd88c08b986f811000001") ] }, delete: false }); and get back expected results?

2) What does the site doc that you're trying to find with the above query look like?

[valerianrossigneux]

1) dosn't return any result in the shell
2) data looks like this

// Activity
{
    "__v": 0,
    "_id": {
        "$oid": "551ecdc03ee254bc0b9eef47"
    },
    "site": {
        "$oid": "5516b924994330f404694a73"
    },
    delete: false
}

// Site
{
    "__v": 0,
    "_id": {
        "$oid": "5516b924994330f404694a73"
    },
    "managers": [{
        "$oid": "521bd88c08b986f811000001"
    }],
    "name": "Site1",
    delete: false
}

[vkarpov15]

Hmm so 1) rules out this being a mongoose issue. Is the output from 2) generated by the mongodb shell? It looks like you're storing ObjectIds as extended JSON object ids rather than as actual object ids.

[valerianrossigneux]

no sorry it is returned from my mongodb GUI, but you get the idea of what the data is.
It might not be possible to select from a collection all "parents" where the specific property "prop" of populated "child" contains the value passed...

I'm running mongodb 2.4.6, maybe that's too old

[vkarpov15]

Ah ok I see what you're trying to do. It's not quite possible to query activities by properties of the corresponding site document - mongodb doesn't support anything like an SQL join. You can make site track the id of the corresponding activity, query on sites, and populate() the activity though.

[acenter2507]

@valerianrossigneux Did you resolved your problem ?

[vadermemo]

one more on the queue of this issue