How to add an extra element in every nested array of a MongoDB object?

Question

I have a MongoDB object like this:

[ 
   { poster_ip: '127.0.0.1',
    post_body: 'example',
    _id: 54fc1f7808bac08f6d25f24b,
    __v: 0 },

  { poster_ip: '127.0.0.1',
    post_body: 'example',
    _id: 54fc1f7808bac08f6d25f24a,
    __v: 0 } 
]

how can i add an extra element to every nested array so it would be like this:

[ 
   { poster_ip: '127.0.0.1',
    post_body: 'example',
    _id: 54fc1f7808bac08f6d25f24a,
    __v: 0,
    newName: NewValue },

  { poster_ip: '127.0.0.1',
    post_body: 'example',
    _id: 54fc1f7808bac08f6d25f24b,
    __v: 0,
    newName: NewValue },
]

I tried this but it didn't work:

for(var i=0; i<JSONobject.length; i++){
    JSONobject[i].newName= NewValue;
}

I'm using node.js, the object is the result i get from a mongodb query.

Here is the function:

exports.Posts = function(UserID, PostID, callback) {

                Post.find( { post: PostID } , function(err, results) {

                var r = results.toObject(); //here i get error 'has no method toObject'

                for (var i=0; i<r.length; i++){
                    r[i].newName = "NewValue";
                }

                console.log(r);
                    //i don't see any changes here with console.log

                    return callback(null, results);
                });
}

EDIT:

After a little more research i found out that the returned Mongoose Document isn't a JSON object, so i'm trying now to convert it to an object.

Iterating based on JSONobject.length and changing results[i]? — thefourtheye
– thefourtheye, Commented Mar 7, 2015 at 16:24
There are serious semantic problems making it hard to follow you. Is JSONobject a Javascript array ? Is it the literal you first write in your question ? Then what's results ? — Denys Séguret
– Denys Séguret, Commented Mar 7, 2015 at 16:25
The for loop you posted looks fine. What makes you think it didn't work? — Pointy
– Pointy, Commented Mar 7, 2015 at 16:25
@Pointy it didn't work because i checked the results after the loop. — Light Flow
– Light Flow, Commented Mar 7, 2015 at 16:28
@dystroy oh, sorry for that, the previous 'results' is the JSON object. I believe that is a javascript array, correct me if i'm wrong. — Light Flow
– Light Flow, Commented Mar 7, 2015 at 16:30

Light Flow · Accepted Answer · 2015-03-08 19:00:53Z

1

I found the answer!!

We need to tell Mongoose that all we need is a plain JavaScript version of the returned results by using lean() in the query chain.

That way Mongoose skips the step of creating the full model instance and we directly get a results we can modify

Like this:

exports.Posts = function(UserID, PostID, callback) {

                Post.find( { post: PostID } , function(err, results) {


                        for (var i=0; i<results.length; i++){
                            results[i].newName = "NewValue";
                        }

                        console.log(results);

                        return callback(null, results);

                }).lean();
}

edited Mar 8, 2015 at 19:00

answered Mar 8, 2015 at 18:54

Light Flow

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1 Comment

Non Plus Ultra Over a year ago

can you believe this.... this was just what I was looking for. JS/Mongo can behave so strange...

Madara's Ghost · Accepted Answer · 2015-03-08 11:11:00Z

0

I'm not sure why a for loop would fail here, because it seems fine to me. But try this:

results = results.map(function(item) {
    item.newName = "NewValue";
    return item;
});

This would create a new array where each original item is appended with the new value.

(As a rule of thumb, using .forEach(), .map(), .filter(), .reduce(), .every() and .some() is almost always superior to for when looping over an array)

answered Mar 8, 2015 at 11:11

Madara's Ghost

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6 Comments

Light Flow Over a year ago

Sorry, didn't work either. I'm starting to believe that my object isn't a JSON object.

Light Flow Over a year ago

The for loop is indeed fine, something else is wrong. Maybe a stupid mistake of mine, i don't know, i'll do my best to find out.

Light Flow Over a year ago

the console.log( Object.prototype.toString.call(results) ); returns object Array

Madara's Ghost Over a year ago

It's possible that the array is an actual array, but the objects are not plain objects. But in that case, it's impossible to answer without a proper reproducible test case.

Light Flow Over a year ago

however, if i do this results.newName = "NewValue"; it works but it adds an element outside of the previous arrays.

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