how exactly to use foreach in nodejs for Mongodb operations

Question

This is my code to get the data from a collection groupname which is initialised with the name of collection. I want to iterate the data stored in doc using foreach loop.

var db = mongojs('login');

    var cursor = db.collection(groupname).find();
    console.log(cursor);

    cursor.each(function(err, doc) {
        console.log(doc._id);

        mongo.collection(doc._id + "group", function(err, collection) {
            collection.remove({"groupname": groupname});
        });
    });

I've tried doing db.collectionname.find().forEach(....), but I've got an error saying that such function doesn't exists. Please help.

UserStack · Accepted Answer · 2015-11-05 11:15:25Z

6

The find() call to fetch the records from Mongo DB is asynchronous. You are trying to use the docs even before the data is available. You should have your forEach loop in the call back of the find().

`

db.collection(groupname).find({}, function(err, doc){
console.log(doc);
doc.forEach(function(err,doc){
    console.log(doc._id);
    db=mongo.collection(doc_id+"group");
    db.remove({"groupname":groupname});
});
});

`

answered Nov 5, 2015 at 11:15

UserStack

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2 Comments

sachin hunur Over a year ago

I tried using your code. The code executes but nothing happens. The control does not enter the function(err,doc). Any idea why?

sachin hunur Over a year ago

hey I realised where i was going wrong. I was deleting the collection before it could select the data. Now i get the message on console which shows the value for doc._id as undefined.

chridam · Accepted Answer · 2015-11-05 11:27:36Z

2

Use the each() method to iterate over all the documents for the find() cursor:

// Grab a cursor
var cursor = db.collection(groupname).find();
console.log(cursor);

// Execute the each command, triggers for each document
cursor.each(function(err, doc) {
    console.log(doc._id);
    // Fetch a collection to remove document
    mongo.collection(doc._id + "group", function(err, collection) {
        collection.remove({"groupname": groupname});
    }
});

-- UPDATE --

Seeing that you are using the mongojs library after your edit, you need to pass a callback function to handle the results of the query since Node.js implements an asynchronous paradigm and almost everything is always a callback which allows your app to be non-blocking and high performing:

// connect now, and worry about collections later
var db = mongojs('login')
var groupcollection = db.collection(groupname)

groupcollection.find({}, function(err, groups) {
    if( err || !groups) console.log("No groups found");
    else groups.forEach( function(group) {
        console.log(group);
        mongo.collection(group._id + "group", function(err, collection) {
            collection.remove({"groupname": groupname});
        });
    });
});

edited Nov 5, 2015 at 11:27

answered Nov 5, 2015 at 10:27

chridam

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7 Comments

sachin hunur Over a year ago

Hi. I get the following error TypeError: cursor.each is not a function

chridam Over a year ago

@sachinhunur Can you edit your question to include the code where the db object is instantiated/initialiased?

chridam Over a year ago

@sachinhunur You did not mention that you are using the mongojs library hence why the above piece of code doesn't work for you.

sachin hunur Over a year ago

How do i make it work with mongojs? I had to use mongojs wrapper cause find() function was not working

chridam Over a year ago

@sachinhunur I've updated my answer to include the mongojs implementation.

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