How to flatten a dynamodb item having nested map in nodejs

Question

I have to write a utility function which reads a dynamodb item and returns a flattened version of that record.

Sample Item

const data={
  "node": {
    "S": "someKey"
  },
  "payload": {
    "M": {
      "name": {
        "S": "some_name"
      },
      "phone": {
        "M": {
          "0": {
            "S": "+126526562562"
          },
          "1": {
            "S": "+126512651652"
          }
        }
      },
      "country": {
        "S": "US"
      }
    }
  }
}

Below is the sample utility function .

const utility = (result, field) => {

  const mapping = result[field];
  const { M: data } = mapping;

  const fieldTypes = ['N','S','M'];
  return Object.fromEntries(
    Object
      .keys(data)
      .map((key) => ({ fieldType: Object.keys(data[key]).shift(), key }))
      .filter((o) => fieldTypes.includes(o.fieldType))
      .map((o) => [o.key, data[o.key][o.fieldType]]),
  );
};

console.log(flattenMap(data,'payload'))

This function works fine if there are no maps inside payload. For example, if I remove the phone attribute from dynamodb item , then I get { name: 'some_name', country: 'US' } which is correct but with phone, I get -

{
  name: 'some_name',
  phone: { '0': { S: '+126526562562' }, '1': { S: '+126512651652' } },
  country: 'US'
}

whereas, what I expect is

{
  name: 'some_name',
  phone: { '0':'+126526562562' }, '1': '+126512651652' },
  country: 'US'
}

What more do I need to add here so that I get the expected response even with a nested map inside payload.

fedonev · Accepted Answer · 2022-04-06 17:41:02Z

1

The easy way: use the SDK v3 DynamoDB utilities to handle conversions:

import { convertToNative } from '@aws-sdk/util-dynamodb';
const converted = convertToNative(payload)

If you insist on DIY: use recursion to deal with arbitrary nesting. The utility function's logic should be invoked recursively for every value in the payload that is a DynamoDB "map" such as { S: '+126526562562' }.

Values are DynamoDB "maps" if they are key-value pairs with keys of ['N','S','M']:

if (val.constructor === Object && Object.keys(val).every(k => fieldTypes.includes(k))) {
  // val is a DynamoDB map, call the function recursively on val
}

answered Apr 6, 2022 at 17:41

fedonev

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