An Hash with aggregation framework

Question

I am using Rails with MongoId, so that will be my syntax language.

My MongoDB objects are something like these:

{ "_id" : "Asset01_*00001", "total" : 124 ...}, { "_id" : "Asset01_*00002", "total" : 99 ...}, {...}

The project operator is:

{"project" => {"_id" => 1, "pair" => {"$add" => {"$_id" => "$total"}} }}

And group operator is:

{"$group" => { "invoice" => { "$push" => "$pair"} }}

But this throws the following error:

the $add operator does not accept an object as an operand

I know the meaning of the error, but have anyone an alternative for this problem?

The result that I would like is:

{ "_id" => 1, "pair" => {"Asset01_*00001" => 124, "Asset01_*00002" => 99 ... }

A hash of {asset_id => number}

Thanks

Answer 1

You want to transform your field values to be keys in the results.

Unfortunately that's not possible, but there is a feature request for it that you can vote up in MongoDB Jira system.