How to insert BSON-ified datetime?

[Evan Zamir]

I want to be able to do aggregation with dates, and I have gotten it to work using the Ruby driver, but not the Node driver. Currently, my code looks like:

var query = {};

var date = new Date();

query['datetime'] = date;

Db.connect(mongoUri, function (err, db) {

        if (!err) {

            db.collection(analyticsCollection, function (err, coll) {

                if (!err) {

                    coll.save(query, {safe:true}, function (err, result) {

                        db.close();

                        res.send(200,result);

                        //console.log(result);

                    });

                } else {

                    res.json(503,{errno:503,msg:'error: collection does not exist.'});

                }

            });

        } else {

            res.json(503,{errno:503,msg:'error: database does not exist.'});

        }

    });

When I try to do this aggregation:

db.analytics.aggregate([{$group:{_id:{day:{$dayOfMonth:"$datetime"}},count:{$sum:1}}}])

I get the following errors:

Fri Jun 14 19:45:21.104 JavaScript execution failed: aggregate failed: {

"errmsg" : "exception: can't convert from BSON type String to Date",

"code" : 16006,

"ok" : 0

} at src/mongo/shell/collection.js:L898

Any ideas about what's going on or how to do this correctly?

[mike o'brien]

Can you post a sample doc from your collection?

This part looks wrong: {$group:{_id:{day:{$dayOfMonth:"$datetime"}} 

You need to break this into two steps. First do a $project to apply the dayOfMonth function to a field, and then do the $group on that field.

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[Evan Zamir]

The date field is simply:

"datetime": "2013-06-15T03:14:01.755Z"

Is it the case that you have to use $project with the node driver? Because I was able to run this aggregation without project when I inserted documents with the Ruby driver.

-eva

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[mike o'brien]

no, it doesn't matter what driver the documents were inserted with, as long as you are using the same structure.

try this:

db.analytics.aggregate([{$project:{day:{$dayOfMonth:"$datetime"}}},   {$group:{_id:"$day",count:{$sum:1}}}])

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[Evan Zamir]

Ok, thanks. I tried that, but it still gives the sam error.

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[Evan Zamir]

I guess my real question is how are you actually supposed to insert a datetime that can be aggregated in this way? Am I currently doing it the right way or not?

On Friday, June 14, 2013 9:09:24 PM UTC-7, mpobrien wrote:

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[mike o'brien]

it looks like you're storing the date as a string, but you need to be storing an actual object of type Date. in node for example you can do:

new Date("2013-06-15T03:14:01.755Z")

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[Evan Zamir]

But I'm currently using new Date() to get the current datetime. I thought that was the correct way to do it.

[Evan Zamir]

I found a way to do what I wanted to do. This seems kind of klugey to me, so if anyone can find a better way, please let me know. My solution uses the underscore.js library (also posted this on SO):

http://stackoverflow.com/questions/17118075/how-to-save-datetime-as-bson-date-using-node-driver/17126378#17126378

var _ = require('underscore');
vary query = {}
query['foo'] = 'bar'

Db.connect(mongoUri, function (err, db) {
        if (!err) {
            db.collection(analyticsCollection, function (err, coll) {
                if (!err) {

                    coll.save(_.extend(query,{"datetime":new Date()}), {safe:true}, function (err, result) {

                        db.close();
                        res.send(200,result);
                        //console.log(result);
                    });
                } else {
                    res.json(503,{errno:503,msg:'error: collection does not exist.'});
                }
            });
        } else {
            res.json(503,{errno:503,msg:'error: database does not exist.'});
        }
    });

Now I can do the aggregation (without needing to use the $project operator):

> db.analytics.aggregate([{$group:{_id:{day:{$dayOfMonth:"$datetime"}}}}])
{ "result" : [ { "_id" : { "day" : 15 } } ], "ok" : 1 }

Hope this helps someone.