Using lookup for ref in array of objects

Working with Data
1

I have the following schema(s):
Customer

{
  _id: "...",
  name: "...",
  email: "...",
}

Hotel:

{
  _id: "...",
  name: "...",
  reviews: [
    {
      _id: "..",
      rating: 1, // number
      content: "...",
      customerId: "..." // ObjectId ref to customer
    },
    {
      _id: "...",
      rating: 1, // number
      content: "...",
      customerId: "..." // ObjectId ref to customer
    }
  ]
}

For simplicity I cut off most of the properties from both models

I am trying to use $lookup to fetch customer data using customerId which is present in the review object within the reviews array, I tried:

Hotel.aggregate(
[
  {
    $lookup: {
      from: "customers",
      localField: "reviews.customerId",
      foreignField: "_id",
      as: "customer"
    }
  }
]
)

But it is not working.

How do I lookup customers using the customerId present in the review object within the reviews array?

2

Can you provide real sample data?

We cannot really experiment easily with

and

Filling the tree dots with real values in order to experiment is time consuming.

3

Sorry for that, and for the late response because the website was on maintenance

Customer:

{
  _id: "6259f7dc78e6ee2c49611c04",
  name: "Customer 1",
  email: "example@example.com",
}

Hotel:

{
  _id: "6259f7dc78e6ee2c49611c00",
  name: "Hotel 1",
  reviews: [
    {
      _id: "6259f7dc78e6ee2c49611c00",
      rating: 1, 
      content: "Great Hotel",
      customerId: "6259f7dc78e6ee2c49611c04" 
    },
    {
      _id: "6259f7dc78e6ee2c49611c01",
      rating: 3.5, 
      content: "Great Hotel",
      customerId: "6259f7dc78e6ee2c49611c04"
    }
  ]
}
4

I would try something like:

  1. $unwind reviews
  2. $lookup with localField:reviews.customerId and as:reviews.customer
  3. if using as:reviews.customer does not work you may need a $set with $mergeObject
  4. recreate the array using $group with $push accumulator.