File Upload API - Step-by-Step Explanation

Introduction

This API allows users to upload, download, view, and delete files using Node.js, Express, and MongoDB. It stores file metadata in a database and saves actual files in a folder called uploads/.

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1. Setting Up the Router

Import Required Modules

const express = require("express");
const router = express.Router();
const File = require("../models/File");
const upload = require("../middleware/upload");
const path = require("path");
const fs = require("fs");

Explanation:

• express → Helps create API routes.
• router → Manages file-related routes.
• File → The MongoDB model for storing file details.
• upload → Middleware for handling file uploads.
• path → Handles file paths.
• fs → Helps read, write, and delete files from the system.

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2. Uploading a File

router.post("/upload", upload.single("file"), async (req, res) => {
  try {
    if (!req.file) {
      return res.status(400).json({ error: "No file uploaded" });
    }

    const newFile = new File({
      filename: req.file.originalname,
      filepath: req.file.path,
      size: req.file.size,
      uploadDate: new Date(),
    });

    await newFile.save();
    res.json({ message: "File uploaded successfully" });
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

Step-by-Step Explanation:

1. router.post("/upload", upload.single("file")) → This handles file uploads.
2. if (!req.file) → Checks if a file was uploaded; if not, it sends an error.
3. new File({...}) → Creates a new entry in MongoDB with:
   • filename: Original file name.
   • filepath: Location where the file is stored.
   • size: File size in bytes.
   • uploadDate: Time of upload.
4. await newFile.save(); → Saves file details in MongoDB.
5. res.json({ message: "File uploaded successfully" }) → Sends a success response.

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3. Getting All Uploaded Files

router.get("/files", async (req, res) => {
  try {
    const files = await File.find();
    res.json(files);
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

Step-by-Step Explanation:

1. router.get("/files") → Handles GET requests to fetch all uploaded files.
2. await File.find(); → Fetches all file records from MongoDB.
3. res.json(files); → Sends the list of files as a JSON response.

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4. Downloading a File

router.get("/download/:filename", async (req, res) => {
  try {
    const file = await File.findOne({ filename: req.params.filename });
    if (!file) {
      return res.status(404).json({ error: "File not found" });
    }
    const filepath = path.join(__dirname, "../uploads", req.params.filename);
    res.download(filepath);
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

Step-by-Step Explanation:

1. router.get("/download/:filename") → Handles download requests by filename.
2. await File.findOne({ filename: req.params.filename }) → Searches for the file in MongoDB.
3. If file not found → Sends a 404 error.
4. path.join(__dirname, "../uploads", req.params.filename) → Constructs the correct file path.
5. res.download(filepath); → Sends the file for download.

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5. Deleting a File

router.delete("/delete/:filename", async (req, res) => {
  try {
    const file = await File.findOne({ filename: req.params.filename });
    if (!file) {
      return res.status(404).json({ error: "File not found" });
    }

    const filePath = path.join(__dirname, "../uploads", file.filename);
    if (fs.existsSync(filePath)) {
      fs.unlinkSync(filePath);
    }

    await File.deleteOne({ filename: req.params.filename });
    res.json({ message: "File deleted successfully" });
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

Step-by-Step Explanation:

1. router.delete("/delete/:filename") → Handles delete requests.
2. await File.findOne({ filename: req.params.filename }) → Looks for the file in MongoDB.
3. If file not found → Sends a 404 error.
4. const filePath = path.join(__dirname, "../uploads", file.filename); → Constructs file path.
5. if (fs.existsSync(filePath)) { fs.unlinkSync(filePath); } → Deletes file from system.
6. await File.deleteOne({ filename: req.params.filename }) → Removes file record from MongoDB.
7. res.json({ message: "File deleted successfully" }) → Sends success response.

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Conclusion

This API provides the following functionalities: ✅ Upload a file (POST /upload) ✅ Get all uploaded files (GET /files) ✅ Download a file (GET /download/:filename) ✅ Delete a file (DELETE /delete/:filename)

Folder Structure

project-folder/
│── models/
│   ├── File.js  # Mongoose model for files
│── middleware/
│   ├── upload.js  # File upload middleware
│── routes/
│   ├── fileRoutes.js  # This API file
│── uploads/  # Folder where uploaded files are stored
│── server.js  # Main server file