Dump a mongo collection

dump-collection.mjs

import 'dotenv/config';

import fs from 'fs';
import path from 'path';
import { fileURLToPath } from 'url';

import { MongoClient } from 'mongodb';

const DB_NAME = '';
const COLLECTION_NAME = '';

const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);

function createSnapshotFile() {
  const now = Date.now();
  const dumpDir = path.join(__dirname, './dump');
  const fileName = `snapshot-${now}.json`;
  const filePath = path.join(dumpDir, fileName);

  if (!fs.existsSync(dumpDir)) {
    fs.mkdirSync(dumpDir);
  }

  const stream = fs.createWriteStream(filePath, { flags: 'a' });
  stream.write('[');

  return stream;
}

(async () => {
  const stream = createSnapshotFile();

  const url = process.env.DATABASE_URL;
  const mongo = new MongoClient(url);
  await mongo.connect();

  console.log('Connected to DB');

  const db = mongo.db(DB_NAME);
  const collection = db.collection(COLLECTION_NAME);

  const cursor = collection.find({});
  const length = await collection.countDocuments();
  let index = 0;

  for await (const record of cursor) {
    const sep = index === length - 1 ? '' : ',';

    console.log(`dumping ${record._id} (${index + 1}/${length})`);
    stream.write(JSON.stringify(record) + sep);
    index++;
  }

  stream.write(']');
  stream.end();

  await mongo.close();

  console.log('Done!');
})();