flattenObjectToMongoDbFormat.ts

export const flattenObjectToMongoDbFormat = (obj: any, parent: String = ''): any => {
  /**
   * When you want to update a MongoDB document, without overriding
   * nested fields that are not specified, you need to specify the 
   * nested fields in the format:
   * `$set: { "parent.nested.key": "value" }`
   * 
   * This method takes a nested object (usually from an incoming API
   * request) and converts it to the nested format.
   */
  const flattened:any = {}
  
  for (const key of Object.keys(obj)) {
    const value = obj[key]
    const flatKey = parent.length ? `${parent}.${key}` : key

    if (typeof value === 'object') {
      const result = flattenObjectToMongoDbFormat(value, flatKey)
      for (const subKey of Object.keys(result)) {
        flattened[`${flatKey}.${subKey}`] = result[subKey] 
      }
    } else {
      flattened[`${key}`] = value
    }
  }

  return flattened
}

// Example usage below:
flattenObjectToMongoDbFormat({
  age: 12,
  job: {
    company: "Acme Corp",
    title: "CEO"
  }
})

// =>
// { 'age': 12, 'job.company': 'Acme Corp', 'job.title': 'CEO' }