How do I rename fields when performing search/projection in MongoDB?

Question

Is it possible to rename the name of fields returned in a find query? I would like to use something like $rename, however I wouldn\'t like to change the documen

Answer 1

As mentioned by @Neil Lunn this can be achieved with an aggregation pipeline:

And starting Mongo 4.2, the $replaceWith aggregation operator can be used to replace a document by a sub-document:

// { level1: { level2: { coordinates: [10, 20] }, b: 4 }, a: 3 }
db.collection.aggregate(
  { $replaceWith: { coords: "$level1.level2.coordinates" } }
)
// { "coords" : [ 10, 20 ] }

Since you mention findOne, you can also limit the number of resulting documents to 1 as such:

db.collection.aggregate([
  { $replaceWith: { coords: "$level1.level2.coordinates" } },
  { $limit: 1 }
])

Prior to Mongo 4.2 and starting Mongo 3.4, $replaceRoot can be used in place of $replaceWith:

db.collection.aggregate(
  { $replaceRoot: { newRoot: { coords: "$level1.level2.coordinates" } } }
)