Include all existing fields and add new fields to document
In 4.2+, you can use the $set aggregation pipeline operator which is nothing other than an alias to $addFieldsadded in 3.4
The
$addFieldsstage is equivalent to a$projectstage that explicitly specifies all existing fields in the input documents and adds the new fields.
db.collection.aggregate([ { "$addFields": { "custom_field": "$obj.obj_field1" } }])
You can use $$ROOT to references the root document. Keep all fields of this document in a field and try to get it after that (depending on your client system: Java, C++, ...)
[ { $project: { custom_field: "$obj.obj_field1", document: "$$ROOT" } }, ... //group, match, and whatever...]
>>> There's something like "include all fields" keyword that I can use in this case or some another solution?
Unfortunaly, there is no operator to "include all fields" in aggregation operation. The only reason, why, because aggregation is mostly created to group/calculate data from collection fields (sum, avg, etc.) and return all the collection's fields is not direct purpose.