mongoose — check if ObjectId exists in an array

Question

Following is an example model:

UserModel == {
    name: String,
    friends: [ObjectId],
}

friends corresponds to a list of id of objects of some other model for example AboutModel.

AboutModel == {
    name: String,
}

User.findOne({name: 'Alpha'}, function(error, user){
    About.find({}, function(error, abouts){ // consider abouts are all unique in this case
        var doStuff = function(index){
            if (!(about.id in user.friends)){
                user.friends.push(about.id);
                about.save();
            }
            if (index + 1 < abouts.length){
                doStuff(index + 1)
            }
        }
        doStuff(0) // recursively...
    })
})

In this case, the condition 'about.id in user.friends` seems to be always false. How? Is this to do with the type of ObjectId or the way it is saved?

Note: ObjectId is short for Schema.ObjectId; I don't know if that's an issue in itself.

JohnnyHK · Accepted Answer · 2013-11-02 13:41:15Z

51

If about.id is a string representation of an ObjectID and user.friends is an array of ObjectIDs, you can check if about.id is in the array using Array#some:

var isInArray = user.friends.some(function (friend) {
    return friend.equals(about.id);
});

The some call will iterate over the user.friends array, calling equals on each one to see if it matches about.id and stop as soon as it finds a match. If it finds a match it returns true, otherwise false.

You can't use something simpler like indexOf because you want to compare the ObjectIDs by value, not by reference.

edited Nov 2, 2013 at 13:41

answered Nov 2, 2013 at 1:57

JohnnyHK

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4 Comments

p0lAris Over a year ago

So basically this is the same as == in a forEach?

p0lAris Over a year ago

TypeError: Object 5274958d4ddfd6341858b2f7 has no method 'equals'.

Capi Etheriel Over a year ago

what if the array is populated?

Capi Etheriel Over a year ago

the arrayLikeProperty.some(document => document.equals(objectId)) works even if the property is populated! thanks a lot for the answer!

gperreymond · Accepted Answer · 2014-08-07 20:53:20Z

3

I use lo-dash and do something like that :

var id_to_found = '...';
var index = _.find(array, function(ch) {
     return ch == id_to_found ;
});
if ( index!=undefined ) {
     // CHILD_ALREADY_EXISTS
} else {
     // OK NOT PRESENTS
}

edited Aug 7, 2014 at 20:53

user1393215

answered Aug 7, 2014 at 18:46

gperreymond

311 bronze badge

1 Comment

user1393215 Over a year ago

Oh, sorry. I thought it was a translation issue or something.

p0lAris · Accepted Answer · 2013-11-02 01:06:24Z

-3

I believe this is a javascript question rather than a Node.js/Mongoose question - so it really doesn't belong in the way it is currently now.

Also, the issue with about.id in user.friends is that the object pointed to by about.id and objects in user.friends are different; and I believe in checks for the equality of the object.

Anyway, the answer is available on stack overflow to check where an element exists in an array —

user.friends.indexOf(about.id) > -1

answered Nov 2, 2013 at 1:06

p0lAris

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4 Comments

Chris Houghton Over a year ago

Doesn't work with ObjectIds, that was why they asked the question

p0lAris Over a year ago

I asked this question.

Chris Houghton Over a year ago

Ah yes apologies for that!

UpTheCreek Over a year ago

That will only work if both your fields are of type string, which from the question they aren't

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