Complete Intro to Databases

NoSQL – Write a Node.js app with MongoDB

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Write a Node.js app with MongoDB

Let's quickly write up a quick Node.js project to help you transfer your skills from the command line to the coding world.

You can access all samples for this project here.

Make a new directory. In that directory run:

npm init -y
npm i express mongodb@3.6.2 express@4.17.1
mkdir static
touch static/index.html server.js
code . # or open this folder in VS Code or whatever editor you want

Let's make a dumb front end that just makes search queries against the backend. In static/index.html put:

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>MongoDB Sample</title>
  </head>
  <body>
    <input type="text" placeholder="Search" id="search" />
    <button id="btn">Search</button>
    <pre>
        <code id="code"></code>
    </pre>

    <script>
      const btn = document.getElementById("btn");
      const code = document.getElementById("code");
      const search = document.getElementById("search");

      btn.addEventListener("click", async () => {
        code.innerText = "loading";

        const res = await fetch(
          "/get?search=" + encodeURIComponent(search.value)
        );
        const json = await res.json();

        code.innerText = "\n" + JSON.stringify(json, null, 4);
      });
    </script>
  </body>
</html>

Normally I'd say don't put a big script tag in there but we're going for simplicity right now. You can refactor this later to something better.

In server.js, put this:

const express = require("express");
const { MongoClient } = require("mongodb");

const connectionString =
  process.env.MONGODB_CONNECTION_STRING || "mongodb://localhost:27017";

async function init() {
  const client = new MongoClient(connectionString, {
    useUnifiedTopology: true,
  });
  await client.connect();

  const app = express();

  app.get("/get", async (req, res) => {
    const db = await client.db("adoption");
    const collection = db.collection("pets");

    const pets = await collection
      .find(
        {
          $text: { $search: req.query.search },
        },
        { _id: 0 }
      )
      .sort({ score: { $meta: "textScore" } })
      .limit(10)
      .toArray();

    res.json({ status: "ok", pets }).end();
  });

  const PORT = process.env.PORT || 3000;
  app.use(express.static("./static"));
  app.listen(PORT);

  console.log(`running on http://localhost:${PORT}`);
}
init();

Potential problem you may see: if you're seeing the error UnhandledPromiseRejectionWarning: MongoError: text index required for $text query (no such collection 'adoption.pets') then you probably have the wrong database name in your code. In my example, I called my database adoption. If you didn't change the name of your database, it will be called test. If you don't know the name of your database, run db in your mongo shell and it should tell you. Once you discover the name of your database, change the line const db = await client.db("<the name of your database here>"); so that it matches the name of your database.

Let's go over a few notes here. To be clear, this is mostly to show you how to connect to MongoDB from code and to show you that all those queries that you learned over the last section apply almost without modification (there are some small differences)

  • We grab a MongoDB connection string out of an environment variable (so you can do that if it's running on a server out in the cloud) otherwise it'll use a local running copy like we will right now.
  • You need to connect to the DB, then to a db (database), then to a collection.
  • You run all the queries at the collection level
  • find, sort, limit, toArray, deleteOne, findOneAndReplace, etc. all work the way you'd expect them to.

That's it! That's a quick Node.js server that connects to MongoDB!