MongoDB Query: Exclude objects from child array?

Question

I'm working on a simple login system for my NodeJS application. For this I have created a structure where one object, a "corporation", holds an array of users. I've done because I plan to use the corporation object to store application session data.

{
    "name": "My Corporation",
    "prefix": "MYCORP",
    "users": [
        {
            "username": "[email protected]",
            "password": "974dae09cd5869958c19e1742117c2f8",
            "name": "Freddly the User"
        },
        {
            "username": "[email protected]",
            "password": "974dae09cd5869958c19e1742117c2f8",
            "name": "Max the Admin"
        }
    ]
}

The problem is when querying after a user (in a log-in scenario) the query, as expected, returns the entire corporation object. Thus I'm exposing all users even though I only want one. As far as security is concerned I guess it isn't a big deal, but I'm more worried about performance. Below is the current query and a very ugly way to delete all users but the one requested.

Ignore the different asserts. Code is very much work-in-progress .. :)

db.collection('kat_corp', function (err, collection) {
    try {
        assert.equal(null, err);

        collection.findOne({
            users: {
                $elemMatch: {
                    username: user.username
                }
            }
        }, function (err, result) {
            if (err) callback(err, false);

            // Delete all other users from the to-be session object
            for (var i = 0; i < result.users.length; i++) {
                if (result.users[i].username != user.username) {
                    delete result.users[i];
                }
            }
            // Will be replaced with success callback
            console.log(result);
        });

    } catch (err) {
        callback(err, false);
    }
});

Can you not add a bunch of users to the database, each having a reference to a 'corporation'? — sje397
– sje397, Commented May 25, 2013 at 11:24
I think that mongoose would help you quite a bit here! You can make a query and select the fields you want exclude in the result — Renato Gama
– Renato Gama, Commented May 25, 2013 at 11:29
While it might be possible using the aggregation framework, it would be far more efficient to split the users into a unique collection, one document per user, with a field for corporation-id. — WiredPrairie
– WiredPrairie, Commented May 25, 2013 at 11:51
Yes, but that sounds an awful lot like a relation based structure? At least it would be a weak link which could be a problem on changes in the corporation collection. Another (small) problem with that approach is that I would have to fetch the corporation in a separate query. — Index
– Index, Commented May 25, 2013 at 12:18
@KGChristensen perhaps this post is useful. It explains the pros and cons of nesting vs separate documents/collections. — robertklep
– robertklep, Commented May 25, 2013 at 14:04

jimoleary · Accepted Answer · 2013-05-25 14:53:52Z

2

If you're using MongoDB 2.2 or greater you can just use the "$" positional operator.

The following query worked for me :

db.collection('kat_corp', function (err, collection){
    collection.findOne({"users.username":user.username}, {'name':1,'users.$': 1}, console.log) 
});

Although I would agree with the other comments that you should probably reconsider your schema...

edited May 25, 2013 at 14:53

answered May 25, 2013 at 14:45

jimoleary

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1 Comment

Index Over a year ago

Thanks, that worked. However I think I'll redesign the schema as suggested in the comments.

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