dev-notes/.NET/ASP.NET/MVC.md

# ASP.NET (Core) MVC Web App

## Project Structure

```txt
Project
|-Properties
| |- launchSettings.json
|
|-wwwroot  --> location of static files
| |-css
| | |- site.css
| |
| |-js
| | |- site.js
| |
| |-lib
| | |- bootstrap
| | |- jquery
| | |- ...
| |
| |- favicon.ico
|
|-Model
| |-ErrorViewModel.cs
| |- Index.cs
| |-...
|
|-Views
| |-Home
| | |- Index.cshtml
| |
| |-Shared
| | |- _Layout.cshtml  --> reusable default page layout
| | |- _ValidationScriptsPartial  --> jquery validation script imports
| |
| |- _ViewImports.cshtml  --> shared imports and tag helpers for all views
| |- _ViewStart.cshtml  --> shared values for all views
| |- ...
|
|-Controllers
| |-HomeController.cs
|
|- appsettings.json
|- Program.cs  --> App entrypoiny
|- Startup.cs  --> App config
```

**Note**: `_` prefix indicates page to be imported.

## Important Files

### `Program.cs`

```cs
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;

namespace App
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();  // start and config ASP.NET App
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();  // config handled in Startup.cs
                });
    }
}
```

### `Startup.cs`

```cs
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace App
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            // set db context for the app using the connection string
            services.AddDbContext<AppDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

            // Captures synchronous and asynchronous Exception instances from the pipeline and generates HTML error responses.
            services.AddDatabaseDeveloperPageExceptionFilter();

            services.AddControllersWithViews();  // MVC Services
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }
            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Home}/{action=Index}/{id?}");
                    // URL => www.site.com/Controller/Action/id
                    // id optional, action is a method of the controller returnig an ActionResult
            });
        }
    }
}
```

### `appsettings.json`

Connection Strings & Secrets.

```json
{
  // WARNING: not for production (use appsecrets.json)
  "ConnectionStrings": {
    "DefaultConnection": "Server=<server>;Database=<database>;Trusted_Connection=true;MultipleActiveResultSets=true;"
  }
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*"
}
```

### `launchsettings.json`

Launch Settings & Deployement Settings.

```json
{
  "iisSettings": {
    "windowsAuthentication": false,
    "anonymousAuthentication": true,
    "iisExpress": {
      "applicationUrl": "http://localhost:55045",
      "sslPort": 44301
    }
  },
  "profiles": {
    "IIS Express": {
      "commandName": "IISExpress",
      "launchBrowser": true,
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development",
        "ASPNETCORE_HOSTINGSTARTUPASSEMBLIES": "Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation"
      }
    },
    "App": {
      "commandName": "Project",
      "dotnetRunMessages": "true",
      "launchBrowser": true,
      "applicationUrl": "https://localhost:5001;http://localhost:5000",
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development",
        "ASPNETCORE_HOSTINGSTARTUPASSEMBLIES": "Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation"
      }
    }
  }
}
```

## Controllers

```cs
using Microsoft.AspNetCore.Mvc;
using App.Models;
using System.Collections.Generic;

namespace App.Controllers
{
    public class CategoryController : Controller
    {
        private readonly AppDbContext _db;

        // get db context through dependency injection
        public CategoryController(AppDbContext db)
        {
            _db = db;
        }

        // GET /Controller/Index
        public IActionResult Index()
        {
            IEnumerable<Entity> enities = _db.Entities;
            return View(Entities);  // pass data to the @model
        }

        // GET /Controller/Create
        public IActionResult Create()
        {
            return View();
        }

        // POST /Controller/Create
        [HttpPost]
        [ValidateAntiForgeryToken]
        public IActionResult Create(Entity entity)  // recieve data from the @model
        {
            _db.Entities.Add(entity);
            _db.SaveChanges();
            return RedirectToAction("Index");  // redirection
        }

        // GET - /Controller/Edit
        public IActionResult Edit(int? id)
        {
            if(id == null || id == 0)
            {
                return NotFound();
            }

            Entity entity = _db.Entities.Find(id);
            if (entity == null)
            {
                return NotFound();
            }

            return View(entity);  // return pupulated form for updating
        }

        // POST /Controller/Edit
        [HttpPost]
        [ValidateAntiForgeryToken]
        public IActionResult Edit(Entity entity)
        {
            if (ModelState.IsValid)  // all rules in model have been met
            {
                _db.Entities.Update(entity);
                _db.SaveChanges();
                return RedirectToAction("Index");
            }

            return View(entity);
        }

        // GET /controller/Delete
        public IActionResult Delete(int? id)
        {
            if (id == null || id == 0)
            {
                return NotFound();
            }

            Entity entity = _db.Entities.Find(id);
            if (entity == null)
            {
                return NotFound();
            }

            return View(entity);  // return pupulated form for confirmation
        }

        // POST /Controller/Delete
        [HttpPost]
        [ValidateAntiForgeryToken]
        public IActionResult Delete(Entity entity)
        {
            if (ModelState.IsValid)  // all rules in model have been met
            {
                _db.Entities.Remove(entity);
                _db.SaveChanges();
                return RedirectToAction("Index");
            }

            return View(entity);
        }
    }
}
```

## Data Validation

### Model Annotations

In `Entity.cs`:

```cs
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Linq;

namespace App.Models
{
    public class Entity
    {
        [DisplayName("Integer Number")]
        [Required]
        [Range(1, int.MaxValue, ErrorMessage = "Error Message")]
        public int IntProp { get; set; }
    }
}
```

### Tag Helpers & Client Side Validation

In `View.cshtml`;

```cs
<form method="post" asp-action="Create">
    <div asp-validation-summary="ModelOnly" class="text-danger"></div>

    <div class="form-group row">
        <div class="col-4">
            <label asp-for="IntProp"></label>
        </div>

        <div class="col-8">
            <input asp-for="IntProp" class="form-control"/>
            <span asp-validation-for="IntProp" class="text-danger"></span>  // error message displyed here
        </div>
    </div>
</form>

// client side validation
@section Scripts{ 
    @{ <partial name="_ValidationScriptsPartial" /> }
}
```

### Server Side Validation

```cs
using Microsoft.AspNetCore.Mvc;
using App.Models;
using System.Collections.Generic;

namespace App.Controllers
{
    public class CategoryController : Controller
    {
        private readonly AppDbContext _db;

        // get db context through dependency injection
        public CategoryController(AppDbContext db)
        {
            _db = db;
        }

        // GET /Controller/Index
        public IActionResult Index()
        {
            IEnumerable<Entity> enities = _db.Entities;
            return View(Entities);  // pass data to the @model
        }

        // GET /Controller/Create
        public IActionResult Create()
        {
            return View();
        }

        // POST /Controller/Create
        [HttpPost]
        [ValidateAntiForgeryToken]
        public IActionResult Create(Entity entity)  // recieve data from the @model
        {
            if (ModelState.IsValid)  // all rules in model have been met
            {
                _db.Entities.Add(entity);
                _db.SaveChanges();
                return RedirectToAction("Index");
            }

            return View(entity);   // return model and display error messages
        }
    }
}
```