MongoDB: can't convert from BSON type EOO to Date

Question

I' trying to use aggregation framework (with ruby) and project the date like this:

db['requests'].aggregate([
{"$project" => {
    _id: 0, 
    method: '$method', 
    user: '$user', 
    year: {'$year' => '$timestamp'}
}}])

the document is like this one:

{
_id: ObjectId("5177d7d7df26358289da7dfd"),
timestamp: ISODate("2013-04-12T03:58:05+00:00"),
method: "POST",
status: "200",
inputsize: "874",
outputsize: "4981",
user: "131"
}

but i get the following error:

Mongo::OperationFailure: Database command 'aggregate' failed: (errmsg: 'exception: can't convert from BSON type EOO to Date'; code: '16006'; ok: '0.0').

This is strange because it works correctly if I run this on the exactly same db which is imported with mongorestore.

Answer 1

The problem was that I was saving some documents without the timestamp field.

Answer 2

If you needed to have some documents without this timestamp field, you could try this (I'm using Javascript/Mongoose notation):

year: { $cond: [{ $ifNull: ['$timestamp', 0] }, { $year: '$deliveryDateEnd' }, -1] }

In this case, every document without the timestamp field would return -1. All the other documents would return the year as expected.