As mentioned in the comment, it appears that mongoose (not mongo) has a limitation of requiring subdocument schemas to be part of an array. So in the case of what is "stat" object, which contains the fg,og etc, I can't just have a single object, but an array of 1. This may be slightly annoying, but I don't think will cause too much issue. Just keep it in mind for projections when querying mongo, and we should be fine.