Most efficient way to use an array of objects to query more objects - MongoDb?

Question

If I have a controller like this:

const Review = require('../models/review')
const Launch = require('../models/launch')

async function getReviewsByUserId (req, res) {
  const { userId } = req.params

  const reviews = await Review.find({ userId }).lean() || []

  return res.status(200).send(reviews.reverse())
}

How can I use the returned reviews to query more objects in the fastest way possible? Example of what I mean:

async function getReviewsByUserId (req, res) {
  const { userId } = req.params

  const reviews = await Review.find({ userId }).lean() || []

  let launches = []
  for (review in reviews) {
    let launch = await Launch.find({launchId: review.launchId})
    launches.push(launch)
  }

  return res.status(200).send(launches.reverse())
}

So as you can see, I simply loop though all my reviews and then use the review.launchId to lookup launches and push each to an array and return that.

Is this efficient? Is there a faster way to accomplish the same thing?

@Tiago Bértolo's answer seems good. Alternatively consider combining the two find()s into a single aggregate() that uses $lookup. — user20042973
– user20042973, Commented Sep 30, 2022 at 16:21

Tiago Bértolo · Accepted Answer · 2022-09-30 15:51:52Z

1

You can use the operator $in to find multiple elements by launchId.

async function getReviewsByUserId (req, res) {
  const { userId } = req.params

  const reviews = await Review.find({ userId }).lean() || []

  let launches = []
  const reviewLaunchIds = reviews.map(review => review.launchId)
  let launch = await Launch.find({launchId:{ $in: reviewLaunchIds })

  return res.status(200).send(launch)
}

answered Sep 30, 2022 at 15:51

Tiago Bértolo

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Comments

Ali Haneen · Accepted Answer · 2022-09-30 17:45:34Z

0

Using aggregate pipelines would be faster and more efficient but a little complicated to use.

The query could be achieved by:

async function getReviewsByUserId(req, res) {
  const { userId } = req.params;

  const launches = await Review.aggregate([
    {
      $match: {
        userId
      }
    },
    {
      $lookup: {
        from: "launches",
        localField: "launchId",
        foreignField: "launchId",
        as: "launches"
      }
    },
    {
      $unwind: {
        path: "$launches",
        preserveNullAndEmptyArrays: true
      }
    },
    { $group: { _id: "$launches._id", data: { $first: "$$ROOT" } } },
    { $replaceRoot: { newRoot: "$data.launches" } }
  ]);

  return res.status(200).send(launches.reverse());
}

edited Sep 30, 2022 at 17:45

answered Sep 30, 2022 at 17:20

Ali Haneen

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