Is it possible to rename _id field after mongo's group aggregation?
You can achieve this by adding a $project stage at the end of your pipeline like this :
{ $project: { _id: 0, name: "$_id", count: 1, sum: 1 }}try it online: mongoplayground.net/p/QpVyh-0I-bP
From mongo v3.4 you could use $addFields in conjunction with $project to avoid to write all the fields in $project that could be very tedious.
This happen in $project because if you include specifically a field, the other fields will be automatically excluded.
Example:
{ $addFields: { my_new_id_name: "$_id" }},{ $project: { _id: 0 }}