On empty DB, I'm trying to ensure that I insert exactly one record like this:

{ short_code: 1 }

... and that concurrent processes doing the same thing will instead increment the short_code.

> db.runCommand({findAndModify: 'short_code', upsert: true, update: { $inc:

{ short_code: 1 }

}, query:

{ short_code: true }

, new: true })
{
"errmsg" : "exception: assertion db/../util/../util/../db/../bson/bsonobjbuilder.h:115",
"code" : 0,
"ok" : 0
}