How to create global objects in MongoDB's V8 engine to be accessible via db.eval?

Question

I'm trying to use MongoDB server-side JavaScript in my nodejs/node-mongodb-native project and just interested how could I save my custom functions in global context of MongoDB and get access to them from db.eval script?

Let's say I have the following unit function:

var myDocumentUtils = {
    doStuff: function (doc) {
       // do stuff with doc ...
       return doc;      
    }
}

And I have the following JavaScript function stored in db.system.js collection:

function processDocument (id) {
    var doc = db.myCollection.findOne({ _id : ObjectId(id)});

    doc = myDocumentUtils.doStuff(doc);   // need access to global myDocumentUtils object     
    db.myCollection.save(doc);

    return doc;
};

I execute processDocument function from my nodejs application like the following:

db.eval('processDocument(54382cb3233283cd3331ca1d)', function (err, doc) {
    if (err) throw err;       
});

So my question is how to save myDocumentUtils in global MongoDB V8 context to be accessible in db.eval function?

Wizard · Accepted Answer · 2014-10-11 14:33:16Z

1

Add the second parameter to processDocument as below:

function processDocument (id, myDocumentUtils) {
    var doc = db.myCollection.findOne({ _id : ObjectId(id)});

    doc = myDocumentUtils.doStuff(doc);   // need access to global myDocumentUtils object     
    db.myCollection.save(doc);

    return doc;
};

Then write db.eval() like this way:

db.eval(function() {
    return processDocument.apply(this, arguments);
}, "54382cb3233283cd3331ca1d", myDocumentUtils);

For your environment, you can add the call back just behind the last parameter myDocumentUtils.

APPEND ---------------------

store below tow functions into db.system.js :

function getMyDocumentUtils() {
    return myDocumentUtils = {
            doStuff: function (doc) {
               // do stuff with doc ...
               return doc;      
            }
        };
}

function processDocument (id) {
    var doc = db.myCollection.findOne({ _id : ObjectId(id)});

    var myDocumentUtils = getMyDocumentUtils(); // added line

    doc = myDocumentUtils.doStuff(doc);   // need access to global myDocumentUtils object     
    db.myCollection.save(doc);

    return doc;
};

Then call db.eval() as your original style.

edited Oct 11, 2014 at 14:33

answered Oct 11, 2014 at 12:32

Wizard

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8 Comments

Erik Over a year ago

thanks for the response but I can't pass JavaScript object to eval functions because I use nodejs. Is there any solutions yet?

Wizard Over a year ago

@Erik, as you are able to store processDocument into database, could you also store another function used to return myDocumentUtils? This function can be called by processDocument.

Erik Over a year ago

could you provide some example please because I little don't understand your suggestion :(

Erik Over a year ago

@Wizardt Thanks you. I do understand your advice and this very cool for me. As I also understand getMyDocumentUtils returns function that evaluates on every call? It it possible to evaluate this function one for performance reasons?

Erik Over a year ago

Can I store two javascript functions in db.system.js?

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