Mongoose - delete subdocument array item

The $pull operator actually just performs the conditions on the array element on which it is operating. It seems that your question might not actually show that you are probably working with an ObjectId value that mongoose creates by default for all array fields.

So you could to your query like this, after importing the ObjectId creation method:

model.findByIdAndUpdate(23, {
    '$pull': {
        'contacts':{ '_id': new ObjectId(someStringValue) }
    }
});

Or in fact you can actually define your "schema" a little better, and mongoose will actually "autocast" the ObjectId for you based on the "type" defined in the schema:

var contactSchema = new Schema({
    approved: Boolean
});

var userSchema = new Schema({
    username: String,
    contacts: [contactSchema]
});

This allows mongoose to "follow the rules" for strictly typed field definitions. So now it knows that you actually have an _id field for each element of the contacts array, and the "type" of that field is actually an ObjectId so it will automatically re-cast "String" values supplied as a true ObjectId.

finaly!

MongoDB:

"imgs" : {"other" : [ {
        "crop" : "../uploads/584251f58148e3150fa5c1a7/photo_2016-11-09_21-38-55.jpg",
        "origin" : "../uploads/584251f58148e3150fa5c1a7/o-photo_2016-11-09_21-38-55.jpg",
        "_id" : ObjectId("58433bdcf75adf27cb1e8608")
                                    }
                            ]
                    },
router.get('/obj/:id',  function(req, res) {
var id = req.params.id;



Model.findOne({'imgs.other._id': id}, function (err, result) {
        result.imgs.other.id(id).remove();
        result.save();            
    });