Model.findById() is returning undefined

Question

I trying to implement a favorite toggle where it saves the favorites in an array, I create a Schema and a router, the code you can see below the problem is when I try to test it on insomnia I'm getting undefined on my console.log(isFavorite). I don't know what could be wrong.

const userSchema = new Schema({
    username: String,
    email: String,
    password: String,
    favorites: [{ type: Schema.Types.ObjectId, ref: "Places" }],
  },
  {
    timestamps: true,
  });

// route

router.put("/favorites/:placeId", (req, res) => {

  const userId = "5ebd13df31430045957db8c3";

  User.findById(userId).then( (user) => {

    const isFavorite = user.favorites.find( (favorite) => {
      return favorite === req.params.placeId;
    });

    console.log(isFavorite);
    console.log(req.params.placeId);

    if (isFavorite) {
      User.findOneAndUpdate(
        { _id: userId },
        {
          $pull: { favorites: req.params.placeId },
        },
        {
          new: true,
        })
        .then((user) => res.json(user))
        .catch((err) => res.status(400).json(err));
    } else {
      User.findOneAndUpdate(
        { _id: userId },
        {
          $push: { favorites: req.params.placeId },
        },
        {
          new: true,
        })
        .then((user) => res.json(user))
        .catch((err) => res.status(400).json(err));
    }
  });
});

Answer 1

this chunk is bad:

User.findById(userId).then((user) => {
    const isFavorite = user.favorites.find((favorite) => {
      return favorite === req.params.placeId;
    });

instead must use populate():

let favorites = await User.findById(userId).populate('favorites');

and then filter favorites by placeId