Accessing the value of a dynamic key in an object

[pungent]

Partial mapping of one of my index is as follows:

"schools": {
  "type": "object",
  "dynamic": true,
  "properties": {}
}

A sample schools object of an existing document is:

"schools": {
  "8291": {
    "max": 11,
    "min": 11
  },
  "3546": {
    "max": 12,
    "min": 10
  },
  "3896": {
    "max": 18,
    "min": 12
  }
}

I have painless script in ES6.2 where dynamically key (e.g. 3896) is computed on runtime and passed to script as a parameter

"script": {
  "params": {
    "key": key
  },
  "source": {
    if (doc.containsKey('schools') && doc.schools.containsKey(key)){
      String dynamic_key = "schools."+key+".min";
      return doc[dynamic_key].value;
    } else {
      return 0;
  }
}

So if passed key value is 3896, then this should return 12. But I get an error message

No field found for [schools.3896.min] in mapping with types [myindexname]

What am I doing wrong? What is the correct way to access a dynamic object where a key name is computed on runtime to fetch its value?

[Igor_Motov]

How many different values under "schools" are you going to have in your index?

[pungent]

@Igor_Motov at a particular time it would be 72, but these kay names changes every week.

[Igor_Motov]

Do you have a daily or weekly indices? If not, increasing the number of dynamic fields is not going to be as sustainable solution.

[pungent]

No, I don't have weekly/daily indices.

[Igor_Motov]

In this case I would try to avoid having dynamic fields here. What kind of searches are you planning to do with data and what are you trying to achieve by using the script?