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

Question

I am getting an issue for running the following aggregate query:

db.snippets.aggregate([ { \'$project\': { month: { \'$month\': \'$created_at\' }} } ])
         


        

Answer 1

This error can also appear if you have incorrectly named your properties in your aggregation relative to what they are in your database.

For example my code was

$group: {
        _id: {$week: "$projects.timeStamp"},
        total: { $sum: "$projects.hours"  }
    }

But I hadn't camelcased timestamp in my database so simply modifying to projects.timestamp fixed it.