Updating a nested record in mongodb array when you don't know the document index

Question

I want to update the record of a nested document, my document looks like this:

[
  {
    "_id": "60753fd9b249ad0dfa1eeb48",
    "name": "Random Name 1",
    "email": "randomname1@zmel.kom",
    "likings": [
      {
        "breakfast": {
          "eat": "oats",
          "drink": "milk"
        }
      },
      {
        "lunch": {
          "eat": "beef",
          "drink": "pepsi"
        }
      },
      {
        "dinner": {
          "eat": "steak",
          "drink": "champagne"
        }
      }
    ]
  },
  {
    "_id": "60753fd9b249ad0dfa1eeb58",
    "name": "Random Name 2",
    "email": "randomname2@zmel.kom",
    "likings": [
      {
        "breakfast": {
          "eat": "cereals",
          "drink": "coffee"
        }
      },
      {
        "lunch": {
          "eat": "salad",
          "drink": "hot-water"
        }
      },
      {
        "dinner": {
          "eat": "biryani",
          "drink": "apple juice"
        }
      }
    ]
  }
]

Now I want to update the value of drink for dinner for Random Name 2 but I don't know the index of dinner, it could be above the lunch, it could be just below the breakfast.
Here's what I have tried in Python :

oid = data[0]                # fetched from flask form
to_be_updated = data[1]      # fetched from flask form
update_value = data[2]       # fetched from flask form
condition = {"_id" : oid}
update_value = {
    "$set" : {
        f"likings.{to_be_updated}.drink" : update_value
    }
}
response = mongo.db.food.update(condition, update_value)

but the error I am getting is:
pymongo.errors.WriteError: Cannot create field 'dinner' in element <complete element description>
What my other strategy that I am planning on using is, only match ID and then update likings by keeping the values that are no needed to be changed as it is and altering that value that i want to change. But this approach seems too obvious and semantically wrong since I am using not updating but updating kind of strategy i.e disturbing the collection schema for no actual reason. Is there a way to do that or should I just continue with what I am thinking

Answer 1

DEMO: MongoDB Playground

First of all, there are errors in your JSON.

JSON

[
  {
    "_id": "60753fd9b249ad0dfa1eeb48",
    "name": "Random Name 1",
    "email": "randomname1@zmel.kom",
    "likings": [
      {
        "breakfast": {
          "eat": "oats",
          "drink": "milk"
        }
      },
      {
        "lunch": {
          "eat": "beef",
          "drink": "pepsi"
        }
      },
      {
        "dinner": {
          "eat": "steak",
          "drink": "champagne"
        }
      }
    ]
  },
  {
    "_id": "60753fd9b249ad0dfa1eeb58",
    "name": "Random Name 2",
    "email": "randomname2@zmel.kom",
    "likings": [
      {
        "breakfast": {
          "eat": "cereals",
          "drink": "coffee"
        }
      },
      {
        "lunch": {
          "eat": "salad",
          "drink": "hot-water"
        }
      },
      {
        "dinner": {
          "eat": "biryani",
          "drink": "apple juice"
        }
      }
    ]
  }
]

Try this:

db.collection.update({
  "name": "Random Name 2",
  "likings.dinner": {
    "$exists": true
  }
},
{
  "$set": {
    "likings.$.dinner.drink": "PEPSI"
  }
})

You can change dinner to whatever field you want to update accordingly.

Answer 2

If possible, refactor likings from a list to an object.

If you can't refactor, check out the $ and $[] positional operators https://docs.mongodb.com/manual/reference/operator/update/positional-all/