flattenObjectToMongoDB.js

const flattenObjectToMongoDbFormat = (obj, ancestors = []) => {
    /**
     * 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 flat = {};
    for (const key of Object.keys(obj)) {
        const value = obj[key];
        if (typeof value === 'object') {
            // Recurse, combine and bubble results upwards
            Object.assign(flat, flattenObjectToMongoDbFormat(value, [...ancestors, key]));
        }
        else {
            // Base case
            const deepKey = [...ancestors, key].join('.');
            flat[deepKey] = value;
        }
    }
    return flat;
};

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

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