Return a nested subdocument inside an array field from a mongodb query

nested-find.js

// Aggregates are a powerful mongodb tool that allows us to craft complex queries.
// In this case it helps prevent repetition in a situation where we would have to
// query a document with a filter, then use a duplicate `Array.find` logic to 
// extract the subdocument we were already expecting to find in the first place.

// Example person document
{
  name: "jason",
  pets: [{
    type: "dog",
    name: "nasus"
  }, {
    type: "bat",
    name: "donga dunderson"
  }]
}

const jasonsDog = await people.aggregate([
  // unwind the pets array so each pet represents a separate document
  // in the pipeline. This results in breaking our documents up like:

  // { name: "jason", pets: { type: "dog", name: "nasus" } }
  // { name: "jason", pets: { type: "bat", name: "donga dunderson" } }
  { "$unwind": "pets" },
  // filter the resulting collection
  { "$match": { name: "jason", "pets.type": "dog" } },
  // replace the root with pets, equivalent to accessing `result.pets` in code
  { "$replaceRoot": { newRoot: "pets" }
}])

console.log(jasonsDog) // { type: "dog", name: "nasus" }

// Note: aggregate pipelines are not available on mongodb atlas free tier