Creating a URL Shortener with C# ASP.NET Core and MongoDB

HomeController.cs

using System;
using System.Diagnostics;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using MongoDB.Driver;
using MongoDB.Driver.Linq;
using shortid;
using url_shortener.Models;

namespace url_shortener.Controllers
{
    public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;
        private readonly IMongoDatabase _mongoDatabase;
        private const string ServiceUrl = "http://localhost:5000";

        public HomeController(ILogger<HomeController> logger)
        {
            _logger = logger;

            var connectionString = "mongodb://localhost:27017/";
            var mongoClient = new MongoClient(connectionString);
            _mongoDatabase = mongoClient.GetDatabase("url-shortener");
        }

        public IActionResult Index()
        {
            return View();
        }

        [HttpGet]
        public async Task<IActionResult> Index(string u)
        {
            // get shortened url collection
            var shortenedUrlCollection = _mongoDatabase.GetCollection<ShortenedUrl>("shortened-urls");
            // first check if we have the short code
            var shortenedUrl = await shortenedUrlCollection
                .AsQueryable()
                .FirstOrDefaultAsync(x => x.ShortCode == u);

            // if the short code does not exist, send back to home page
            if (shortenedUrl == null)
            {
                return View();
            }

            return Redirect(shortenedUrl.OriginalUrl);
        }

        [HttpPost]
        public async Task<IActionResult> ShortenUrl(string longUrl)
        {
            // get shortened url collection
            var shortenedUrlCollection = _mongoDatabase.GetCollection<ShortenedUrl>("shortened-urls");
            // first check if we have the url stored
            var shortenedUrl = await shortenedUrlCollection
                .AsQueryable()
                .FirstOrDefaultAsync(x => x.OriginalUrl == longUrl);

            // if the long url has not been shortened
            if (shortenedUrl == null)
            {
                var shortCode = ShortId.Generate(length: 8);
                shortenedUrl = new ShortenedUrl
                {
                    CreatedAt = DateTime.UtcNow,
                    OriginalUrl = longUrl,
                    ShortCode = shortCode,
                    ShortUrl = $"{ServiceUrl}?u={shortCode}"
                };
                // add to database
                await shortenedUrlCollection.InsertOneAsync(shortenedUrl);
            }

            return View(shortenedUrl);
        }

        public IActionResult Privacy()
        {
            return View();
        }

        [ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
        public IActionResult Error()
        {
            return View(new ErrorViewModel {RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier});
        }
    }
}

Index.cshtml

@{
    ViewData["Title"] = "Home Page";
}

<div class="text-center">
    <h1 class="display-4">Welcome</h1>
    <p>A url shortener built with ASP.NET Core and Mongo DB</p>
</div>

<div style="width: 100%; margin-top: 60px;">
    <div style="width: 65%; margin-left: auto; margin-right: auto;">
        <form id="form" style="text-align: center;" asp-action="ShortenUrl" method="post">
            <input
                type="text"
                placeholder="Enter Url ..."
                style="width: 100%; border-radius: 5px; height: 45px;"
                name="longUrl"/>

            <button
                style="background-color: darkgreen; color: white; padding: 10px; margin-top: 25px; border-radius: 8px;"
                type="submit">
                Shorten Url
            </button>
        </form>
    </div>
</div>

ShortenedUrl.cs

using System;
using MongoDB.Bson;
using MongoDB.Bson.Serialization.Attributes;

namespace url_shortener.Models
{
    public class ShortenedUrl
    {
        [BsonId]
        public ObjectId Id { get; set; }
        public string OriginalUrl { get; set; }
        public string ShortCode { get; set; }
        public string ShortUrl { get; set; }
        public DateTime CreatedAt { get; set; }
    }
}

ShortenUrl.cshtml

@model ShortenedUrl;

@{
    ViewData["Title"] = "Shortened Url";
}

<div style="width: 100%; padding: 30px;">
    <div>
        <div>Short Code: @Model.ShortCode</div>
        <div>Short Url: @Model.ShortUrl</div>
        <div>Long Url: @Model.OriginalUrl</div>
    </div>
</div>