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

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.

[vadermemo]

one more on the queue of this issue