Storing a Javascript function in a mongoDB database for retrieval later.

[Adam Griffiths]

Hi,

I am using the Node.js driver for MongoDB.

I want to know if there is a way to store a function in a mongodb database, retrieve it later and then run it from within the node.js script. Currently I've been trying the below: 

var mongo = require("mongodb").MongoClient;

mongo.connect("mongodb://localhost:27017/testdb", function(err, db){

    var printHelloWorld = function(){
        console.log("Hello World!");
    }

    var testData = {_id: "testData", data: printHelloWorld};

    db.collection("test").insertOne(testData, function(err, result){

        console.log("added data");

        db.collection("test").find({_id: "test data"}).toArray(function(err, docs){
            docs[0].printHelloWorld();

        });
    });

        

});

If I try to run this I get the following error:

TypeError: Cannot read property 'printHelloWorld' of undefined

    at /home/ubuntu/workspace/test2.js:16:20

    at handleCallback (/home/ubuntu/workspace/node_modules/mongodb/lib/utils.js:96:12)

    at /home/ubuntu/workspace/node_modules/mongodb/lib/cursor.js:835:16

    at handleCallback (/home/ubuntu/workspace/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:159:5)

    at setCursorNotified (/home/ubuntu/workspace/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:490:3)

    at /home/ubuntu/workspace/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:561:16

    at queryCallback (/home/ubuntu/workspace/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:241:5)

    at Callbacks.emit (/home/ubuntu/workspace/node_modules/mongodb/node_modules/mongodb-core/lib/topologies/server.js:119:3)

    at null.messageHandler (/home/ubuntu/workspace/node_modules/mongodb/node_modules/mongodb-core/lib/topologies/server.js:295:23)

    at Socket.<anonymous> (/home/ubuntu/workspace/node_modules/mongodb/node_modules/mongodb-core/lib/connection/connection.js:285:22)

What can I do differently to store a function, or is it not possible?

[Rhys Campbell]

You can although MongoDB don't seem very keen to encourage it...

https://docs.mongodb.com/manual/tutorial/store-javascript-function-on-server/

[Adam Griffiths]

On Monday, 9 May 2016 10:11:48 UTC+1, Rhys Campbell wrote:

You can although MongoDB don't seem very keen to encourage it...

https://docs.mongodb.com/manual/tutorial/store-javascript-function-on-server/

I've already looked at this but it doesn't seem to work either, if I perform an identical operation but change the collection to system.js then I get the same error. 

If I pull code straight from the example in the page you linked and run it I instead get the following error

TypeError: Cannot read property 'js' of undefined

    at /home/ubuntu/workspace/test2.js:5:14

    at /home/ubuntu/workspace/node_modules/mongodb/lib/mongo_client.js:519:11

    at nextTickCallbackWith0Args (node.js:420:9)

    at process._tickCallback (node.js:349:13)

 

[Adam Griffiths]

On Monday, 9 May 2016 10:11:48 UTC+1, Rhys Campbell wrote:

You can although MongoDB don't seem very keen to encourage it...

https://docs.mongodb.com/manual/tutorial/store-javascript-function-on-server/

Also this example seems to be only for running functions within the MongoDB server itself, but I am looking to retrieve functions and then run them in node.js instead. 

[Adam Griffiths]

After some more digging I have found this class that allows you to simply convert a function to a code object and that can be stored into the database.

After retrieval is there a way to easily convert from the code object back to a function that can be run?   

[Wan Bachtiar]

I am looking to retrieve functions and then run them in node.js instead.

After retrieval is there a way to easily convert from the code object back to a function that can be run?

Hi Adam,

Generally, it is not recommended to dynamically evaluate code at runtime as it could be a potential security risk and performance issue.

Although if you have a good use case for it, you could store the function string into the database and construct later using Function() class. Using your code example:

var testData = {_id: "testData", data: "console.log('Hello World')"};

db.collection("test").insertOne(testData, function(err, result){
    console.log("added data");
    db.collection("test").findOne({_id: "testData"}, function(err, doc){
        func = new Function(doc.data);
        func();
    });
});

Please see Function constructor to find out more.

You may also be interested to know that the next session for free online course M101JS: MongoDB for Node.js Developers is starting in 24th May.

Best regards,

Wan.

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