Mongoose を AWS Lambda と共に使用する方法

AWS Lambda は、個々のサーバーを管理せずに任意の関数を動かすための一般的なサービスです。AWS Lambda 関数で Mongoose を使用するのは簡単です。以下に、MongoDB インスタンスに接続して単一のドキュメントを見つけるサンプル関数が示されています。

const mongoose = require('mongoose');

let conn = null;

const uri = 'YOUR CONNECTION STRING HERE';

exports.handler = async function(event, context) {
  // Make sure to add this so you can re-use `conn` between function calls.
  // See https://www.mongodb.com/blog/post/serverless-development-with-nodejs-aws-lambda-mongodb-atlas
  context.callbackWaitsForEmptyEventLoop = false;

  // Because `conn` is in the global scope, Lambda may retain it between
  // function calls thanks to `callbackWaitsForEmptyEventLoop`.
  // This means your Lambda function doesn't have to go through the
  // potentially expensive process of connecting to MongoDB every time.
  if (conn == null) {
    conn = mongoose.createConnection(uri, {
      // and tell the MongoDB driver to not wait more than 5 seconds
      // before erroring out if it isn't connected
      serverSelectionTimeoutMS: 5000
    });

    // `await`ing connection after assigning to the `conn` variable
    // to avoid multiple function calls creating new connections
    await conn.asPromise();
    conn.model('Test', new mongoose.Schema({ name: String }));
  }

  const M = conn.model('Test');

  const doc = await M.findOne();
  console.log(doc);

  return doc;
};

接続ヘルパー

上記のコードは 1 つの Lambda 関数ではうまく動作しますが、同じ接続ロジックを複数の Lambda 関数で再利用したい場合はどうでしょうか？以下の関数をエクスポートできます。

const mongoose = require('mongoose');

let conn = null;

const uri = 'YOUR CONNECTION STRING HERE';

exports.connect = async function() {
  if (conn == null) {
    conn = mongoose.createConnection(uri, {
      serverSelectionTimeoutMS: 5000
    });

    // `await`ing connection after assigning to the `conn` variable
    // to avoid multiple function calls creating new connections
    await conn.asPromise();
  }

  return conn;
};

mongoose.connect() の使用

mongoose.connect() も使用し、mongoose.model() でモデルを作成することもできます。

const mongoose = require('mongoose');

let conn = null;

const uri = 'YOUR CONNECTION STRING HERE';

exports.connect = async function() {
  if (conn == null) {
    conn = mongoose.connect(uri, {
      serverSelectionTimeoutMS: 5000
    }).then(() => mongoose);

    // `await`ing connection after assigning to the `conn` variable
    // to avoid multiple function calls creating new connections
    await conn;
  }

  return conn;
};