MongoDB - Rename fields in aggregation pipeline

Question

This is the document I get after an aggregation query:

{
  _id: <some id>,
  name: 'xxxx',
  sales: {
    saleDate: 'dddddd',
    saleValue: 9999
  }
}

I need to rename the sales field to sale, I know I can use a projection at the end of my aggregation pipeline like this:

[
  //... other aggregation stages before,
  {
    $project: {
      sale: '$sales'
    }
  }
]

But the problem with that approach is that now I have to specify all the remaining fields in the projection otherwise I will get only the sale field in the response, in this example I only have 3 fields but in my project I have much more than that.

So is there another way to rename a field in an aggregation pipeline?

Answer 1

Try this:

{
  $set: {
    sale: '$sales'
    sales: '$$REMOVE'
  }
}