How . populate searches the data

Question

I have a question about performance using Mongoose.

Suppose the following models:

const Disciplina = new Schema({
  titulo: {
    type: String,
  }
})

const Assunto = new Schema({
  disciplina: {
    type: ObjectId,
    ref: 'Disciplina',
  }
})

What is the best way to seek the subjects and titles of the disciplines of each subject?

1.

  Assunto.find({}).populate('disciplina')

  const assuntos = Assunto.find({})
  const disciplinasIds = assuntos.map(it => it.disciplina)

  const disciplinas = Disciplina
                        .find({ _id: {$in: disciplinasIds}})                     

and then manually insert the discipline on my return

---

It is obvious that the first way is simpler and clean, but my doubt is regarding the performance of .populate. If I have two "Subjects" with the same discipline id, two will be made finds? How does it work?

Thank you!

Answer 1

I did a bigger search, I used the flag debug from Mongoose and I saw that it basically makes the case 2. under the cloths.

Then you better use the populate