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Integrating LowDB for Persistency into an Existing Express.js API

Introduction​

LowDB is a lightweight, file-based database that can be easily integrated into an existing Express.js API to provide persistency. This guide outlines the necessary steps to add LowDB to an already functioning API.

Prerequisites​

Ensure your existing Express.js API is set up and running. You'll need:

Steps to Integrate LowDB​

1. Install LowDB​

Navigate to your project directory and install LowDB:

npm install lowdb

2. Configure LowDB in Your API​

Modify your server.js (or equivalent) to include LowDB.

Import Express and LowDB (ES Module Syntax)​

If you're using ES modules (type": "module" in package.json), import Express and LowDB as follows:

import express from "express";
import { Low } from "lowdb";
import { JSONFile } from "lowdb/node";

const app = express();
app.use(express.json());

const adapter = new JSONFile("db.json");
const db = new Low(adapter);

async function initDB() {
  await db.read();
  if (!db.data) {
    db.data = { users: [] }; // Ensure default data exists
    await db.write();
  }
}
await initDB();

3. Modify Existing Routes to Use LowDB​

Update your existing API routes to read from and write to LowDB.

Example: Fetching Data​

Replace existing logic with LowDB's db.read():

app.get("/users", async (req, res) => {
  await db.read();
  res.json(db.data.users);
});

Example: Adding Data​

Modify your POST route to save data to LowDB:

app.post("/users", async (req, res) => {
  await db.read();
  const newUser = req.body;
  db.data.users.push(newUser);
  await db.write();
  res.status(201).json(newUser);
});

Example: Updating Data​

Modify your PUT route to update an existing entry:

app.put("/users/:id", async (req, res) => {
  await db.read();
  const userId = req.params.id;
  const updatedUser = req.body;
  const index = db.data.users.findIndex((user) => user.id === userId);

  if (index !== -1) {
    db.data.users[index] = { ...db.data.users[index], ...updatedUser };
    await db.write();
    res.json(db.data.users[index]);
  } else {
    res.status(404).json({ message: "User not found" });
  }
});

Example: Deleting Data​

Modify your DELETE route to remove an entry:

app.delete("/users/:id", async (req, res) => {
  await db.read();
  const userId = req.params.id;
  db.data.users = db.data.users.filter((user) => user.id !== userId);
  await db.write();
  res.status(204).send();
});

4. Test the Updated API​

Use tools like Postman or curl to test the new persistency.

Get Users​

curl -X GET http://localhost:3000/users

Add a User​

curl -X POST http://localhost:3000/users \
     -H "Content-Type: application/json" \
     -d '{"id": "1", "name": "John Doe"}'

Update a User​

curl -X PUT http://localhost:3000/users/1 \
     -H "Content-Type: application/json" \
     -d '{"name": "John Updated"}'

Delete a User​

curl -X DELETE http://localhost:3000/users/1

Conclusion​

By following these steps, you have successfully integrated LowDB into your existing Express.js API, allowing for lightweight and persistent data storage. This method is ideal for small applications, prototypes, or local development environments.