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commit 4c2115283083520b8c1556b2e0c18dbe09065fe9 Author: Marcello Lamonaca Date: Sun Jan 31 11:05:37 2021 +0100 Upload of pre-existing files diff --git a/.NET/ASP.NET/MVC.md b/.NET/ASP.NET/MVC.md new file mode 100644 index 0000000..10ef678 --- /dev/null +++ b/.NET/ASP.NET/MVC.md @@ -0,0 +1,414 @@ +# 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(); // 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(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=;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 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 + + +// client side validation +@section Scripts{ + @{ } +} +``` + +### 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 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 + } + } +} +``` diff --git a/.NET/ASP.NET/REST API.md b/.NET/ASP.NET/REST API.md new file mode 100644 index 0000000..47d0c12 --- /dev/null +++ b/.NET/ASP.NET/REST API.md @@ -0,0 +1,336 @@ +# ASP .NET REST API + +## Startup class + +- Called by `Program.cs` + +```cs +using Microsoft.AspNetCore.Builder; +using Microsoft.AspNetCore.Hosting; +using Microsoft.Extensions.Configuration; +using Microsoft.Extensions.DependencyInjection; +using Microsoft.Extensions.Hosting; + +namespace +{ + 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) + { + services.AddControllers(); // controllers w/o views + //or + sevices.AddControllersWithViews(); // MVC Controllers + } + + // 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(); + } + + app.UseHttpsRedirection(); + + app.UseRouting(); + + app.UseAuthorization(); + + app.UseEndpoints(endpoints => + { + endpoints.MapControllers(); + }); + } + } +} +``` + +## DB Context (EF to access DB) + +NuGet Packages to install: + +- `Microsoft.EntityFrameworkCore` +- `Microsoft.EntityFrameworkCore.Tools` +- `Microsoft.EntityFrameworkCore.Design` *or* `Microsoft.EntityFrameworkCore..Design` +- `Microsoft.EntityFrameworkCore.` + +In `AppDbContext.cs`: + +```cs +using .Model; +using Microsoft.EntityFrameworkCore; + +namespace .Repo +{ + public class AppDbContext : DbContext + { + public AppDbContext(DbContextOptions options) : base(options) + { + + } + //DBSet represents the collection of all entities in the context, or that can be queried from the database, of a given type + public DbSet entities { get; set; } + } +} +``` + +In `appsettings.json`: + +```json +{ + "Logging": { + "LogLevel": { + "Default": "Information", + "Microsoft": "Warning", + "Microsoft.Hosting.Lifetime": "Information" + } + }, + "AllowedHosts": "*", + "ConnectionStrings": { + "CommanderConnection" : "Server=;Database=;UID=;Pwd=" + } +} +``` + +In `Startup.cs`: + +```cs +// This method gets called by the runtime. Use this method to add services to the container. +public void ConfigureServices(IServiceCollection services) +{ + // SqlServer is the db used in this example + services.AddDbContext(option => option.UseSqlServer(Configuration.GetConnectionString("CommanderConnection"))); + services.AddControllers(); +} +``` + +### Migrations + +- Mirroring of model in the DB. +- Will create & update DB Schema if necessary + +In Packge Manager Shell: + +```ps1 +add-migrations +update-database # use the migrations to modify the db +``` + +## Repository + +In `IEntityRepo`: + +```cs +using .Model; +using System.Collections.Generic; + +namespace .Repository +{ + public interface IEntityRepo + { + IEnumerable SelectAll(); + Entity SelectOneById(int id); + + ... + } +} +``` + +In `EntityRepo`: + +```cs +using .Model; +using System.Collections.Generic; + +namespace .Repo +{ + public class EntityRepo : IEntityRepo + { + private readonly AppDbContext _context; + + public EntityRepo(AppDbContext context) + { + _context = context; + } + + public IEnumerable SelectAll() + { + return _context.Entities.ToList(); // linq query (ToList()) becomes sql query + } + + public Entity SelectOneById(int id) + { + return _context.Entities.FirstOrDefault(p => p.Id == id); + } + + ... + } +} +``` + +## Data Transfer Objects (DTOs) + +A **DTO** is an object that defines how the data will be sent and recieved over the network (usually as JSON). +Without a DTO the JSON response (or reqest) could contain irrilevant, wrong or unformatted data. +Moreover, by decoupling the JSON response from the actual data model, it's possible to change the latter without breaking the API. +DTOs must be mapped to the internal methods. + +Required NuGet Packages: + +- AutoMapper.Extensions.Microsoft.DependencyInjection + +In `StartUp.cs`: + +```cs +using AutoMapper; + +// ... + +public void ConfigureServices(IServiceCollection services) +{ + // other services + + services.AddAutoMapper(AppDomain.CurrentDomain.GetAssemblies()); // set automapper service +} +``` + +In `EntityDTO.cs`: + +```cs +namespace .DTOs +{ + // define the data to be serialized in JSON (can differ from model) + public class EntityCrudOpDTO // e.g: EntityReadDTO, ... + { + // only properties to be serialized + } +} +``` + +In `EntitiesProfile.cs`: + +```cs +using AutoMapper; +using .DTOs; +using .Model; + +namespace .Profiles +{ + public class EntitiesProfile : Profile + { + public EntitiesProfile() + { + CreateMap(); // map entity to it's DTO + } + } +} +``` + +## Controller (No View) + +Uses [Dependency Injection](https://en.wikipedia.org/wiki/Dependency_injection) to recieve a suitable implementation of `IEntityRepo`, + +### Service Lifetimes + +- `AddSignleton`: same for every request +- `AddScoped`: created once per client +- `Transient`: new instance created every time + +In `Startup.cs`: + +```cs +// This method gets called by the runtime. Use this method to add services to the container. +public void ConfigureServices(IServiceCollection services) +{ + services.AddControllers(); + services.AddScoped(); // map the interface to its implementation, needed for dependency injection +} +``` + +### Request Mappings + +```cs +using .Model; +using .Repo; +using Microsoft.AspNetCore.Mvc; +using System.Collections.Generic; + +namespace .Controllers +{ + [Route("api/endpoint")] + [ApiController] + public class EntitiesController : ControllerBase // MVC controller w/o view + { + private readonly ICommandRepo _repo; + private readonly IMapper _mapper; // AutoMapper class + + public EntitiesController(IEntityRepo repository, IMapper mapper) // injection og the dependency + { + _repo = repository; + _mapper = mapper + } + + [HttpGet] // GET api/endpoint + public ActionResult> SelectAllEntities() + { + var results = _repo.SelectAll(); + + return Ok(_mapper.Map(results)); // return an action result OK (200) with the results + } + + // default binding source: [FromRoute] + [HttpGet("{id}")] // GET api/endpoint/{id} + public ActionResult SelectOneEntityById(int id) + { + var result = _repo.SelectOneById(id); + + if(result != null) + { + return Ok(_mapper.Map(result)); // transfrom entity to it's DTO + } + + return NotFound(); // ActionResult NOT FOUND (404) + } + } +} +``` + +## Controller (With View) + +```cs +using .Model; +using Microsoft.AspNetCore.Mvc; +using System; +using System.Collections.Generic; +using System.Linq; +using System.Threading.Tasks; + +namespace .Controllers +{ + [Route("api/endpoint")] + [ApiController] + public class EntitiesController : Controller + { + private readonly AppDbContext _db; + + public EntitiesController(AppDbContext db) + { + _db = db; + } + + [HttpGet] + public IActionResult SelectAll() + { + return Json(new { data = _db.Entities.ToList() }); // json view + } + } +} +``` diff --git a/.NET/ASP.NET/Razor Pages.md b/.NET/ASP.NET/Razor Pages.md new file mode 100644 index 0000000..0c862cb --- /dev/null +++ b/.NET/ASP.NET/Razor Pages.md @@ -0,0 +1,384 @@ +# Razor Pages + +## Project Structure + +```txt +Project +|-Properties +| |- launchSettings.json +| +|-wwwroot --> static files +| |-css +| | |- site.css +| | +| |-js +| | |- site.js +| | +| |-lib +| | |- jquery +| | |- bootstrap +| | |- ... +| | +| |- favicon.ico +| +|-Pages +| |-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 +| |- Index.cshtml +| |- Index.cshtml.cs +| |- ... +| +|- appsettings.json --> application settings +|- Program.cs --> App entrypoint +|- Startup.cs +``` + +**Note**: `_` prefix indicates page to be imported + +Razor Pages components: + +- Razor Page (UI/View - `.cshtml`) +- Page Model (Handlers - `.cshtml.cs`) + +in `Index.cshtml`: + +```cs +@page // mark as Razor Page +@model IndexModel // Link Page Model + +@{ + ViewData["Title"] = "Page Title" // same as Page Title +} + +// body contents +``` + +in `Page.cshtml.cs`: + +```cs +using Microsoft.AspNetCore.Mvc.RazorPages; +using Microsoft.Extensions.Logging; + +namespace App.Pages +{ + public class IndexModel : PageModel + { + // HTTP Method + public void OnGet() { } + + // HTTP Method + public void OnPost() { } + } +} +``` + +## 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(); // 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) + { + // use Razor Pages + // runtime compilation needs Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation pkg + services.AddRazorPages().AddRazorRuntimeCompilation(); + + // set db context for the app using the connection string + services.AddDbContext(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"))); + + // Captures synchronous and asynchronous Exception instances from the pipeline and generates HTML error responses. + services.AddDatabaseDeveloperPageExceptionFilter(); + + } + + // 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.MapRazorPages(); + }); + } + } +} +``` + +### `appsettings.json` + +Connection Strings & Secrets. + +```json +{ + "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:51144", + "sslPort": 44335 + } + }, + "profiles": { + "IIS Express": { + "commandName": "IISExpress", + "launchBrowser": true, + "environmentVariables": { + "ASPNETCORE_ENVIRONMENT": "Development" + } + }, + "BookListRazor": { + "commandName": "Project", + "dotnetRunMessages": "true", + "launchBrowser": true, + "applicationUrl": "https://localhost:5001;http://localhost:5000", + "environmentVariables": { + "ASPNETCORE_ENVIRONMENT": "Development" + } + } + } +} +``` + +## Razor Page + +```cs +using Microsoft.AspNetCore.Mvc.RazorPages; +using Microsoft.Extensions.Logging; + +namespace App.Pages +{ + public class IndexModel : PageModel + { + private readonly ApplicationDbContext _db; // EF DB Context + + // Get DBContex through DI + public IndexModel(ApplicationDbContext db) + { + _db = db; + } + + [BindProperty] // assumed to be recieved on POST + public IEnumerable Entities { get; set; } + + // HTTP Method Handler + public aysnc Task OnGet() + { + // get data from DB (example operation) + Entities = await _db.Entities.ToListAsync(); + } + + // HTTP Method Handler + public async Task OnPost() + { + if (ModelState.IsValid) + { + // save to DB (example operation) + await _db.Entities.AddAsync(Entity); + await _db.SaveChangesAsync(); + + return RedirectToPage("Index"); + } + else + { + return Page(); + } + } + } +} +``` + +## Routing + +Rules: + +- URL maps to a physical file on disk +- Razor paged needs a root folder (Default "Pages") +- file extension not included in URL +- `Index.cshtml` is enrtypoint and default document (missing file in URL redirects to index) + +| URL | Maps TO | +|------------------------|----------------------------------------------------| +| www.domain.com | /Pages/Index.cshtml | +| www.doamin.com/Index | /Pages/Index.html | +| www.domain.com/Account | /Pages/Account.cshtml, /Pages/Account/Index.cshtml | + +## 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 + + +// client side validation +@section Scripts{ + @{ } +} +``` + +### Server Side Validation + +```cs +using Microsoft.AspNetCore.Mvc; +using App.Models; +using System.Collections.Generic; + +namespace App.Controllers +{ + public class IndexModel : PageModel + { + private readonly ApplicationDbContext _db; + + // get db context through dependency injection + public IndexModel(AppDbContext db) + { + _db = db; + } + + [BindProperty] + public Entity Entity { get; set; } + + public async Task OnGet(int id) + { + Entity = await _db.Entities.FindAsync(id); + } + + public async Task OnPost() + { + if (ModelState.IsValid) + { + + await _db.SaveChangesAsync(); + + return RedirectToPage("Index"); + } + else + { + return Page(); + } + } + } +} +``` diff --git a/.NET/ASP.NET/Razor Syntax.md b/.NET/ASP.NET/Razor Syntax.md new file mode 100644 index 0000000..1809542 --- /dev/null +++ b/.NET/ASP.NET/Razor Syntax.md @@ -0,0 +1,164 @@ +# [Razor Syntax](https://docs.microsoft.com/en-us/aspnet/core/mvc/views/razor) + +## Markup + +```cs +@page // set this as razor page + +@model .Models.Entity // if MVC set type of elements passed to the view +@model Model // if Razor page set underlying class + +@* razor comment *@ + +// substituite @variable with it's value +@variable + +@{ + // razor code block + // can contain C# or HTML + + Model // acces to passed @model (MVC) +} + +@if (condition) { } + +@for (init, condition, iteration) { } + +@Model.Property // display Property value (MVC) +``` + +--- + +## Tag Helpers (ASP.NET Core) + +**Tag helpers** are reusable components for automating the generation of HTML in Razor Pages. Tag helpers target specific HTML tags. + +Example: + +```html + +Home +``` + +### Managing Tag Helpers + +The `@addTagHelper` directive makes Tag Helpers available to the view. Generally, the view file is `Pages/_ViewImports.cshtml`, which by default is inherited by all files in the `Pages` folder and subfolders, making Tag Helpers available. + +```cs +@using +@namespace .Pages // or .Models +@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers +``` + +The first parameter after `@addTagHelper` specifies the Tag Helpers to load (`*` for all Tag Helpers), and the second parameter (e.g. `Microsoft.AspNetCore.Mvc.TagHelpers`) specifies the assembly containing the Tag Helpers. +`Microsoft.AspNetCore.Mvc.TagHelpers` is the assembly for the built-in ASP.NET Core Tag Helpers. + +#### Opting out of individual elements + +It's possible to disable a Tag Helper at the element level with the Tag Helper opt-out character (`!`) + +```cshtml + + +``` + +### Explicit Tag Helpers + +The `@tagHelperPrefix` directive allows to specify a tag prefix string to enable Tag Helper support and to make Tag Helper usage explicit. + +```cshtml +@tagHelpersPrefix th: +``` + +### Important Tag Helpers (`asp-`) & HTML Helpers (`@Html`) + +[Understanding Html Helpers](https://stephenwalther.com/archive/2009/03/03/chapter-6-understanding-html-helpers) + +```cs +@model .Models.Entity + +// Display the name of the property +@Html.DisplayNameFor(model => model.EntityProp) +@nameof(Model.EntityProp) + +// Display the value of the property +@Html.DisplayFor(model => model.EntityProp) +@Model.EntityProp + + + // use the property as the label, eventyally w/ [DysplayName("...")] + + @Html.LabelFor() + + // automatically set the value at form compilation and submission + + @Html.EditorFor() + + +// route config is {Controller}/{Action}/{Id?} +Link // link to /Controller/Action +Link // link to /Controller/Action/Id +@Html.ActionLink("", "", "", new { @HTmlAttribute = value, Id = value }) // link to /Controller/Action/Id + +// link to /Controller/Action?queryParameter=value +@Html.ActionLink("", "", "", new { @HTmlAttribute = value, queryParameter = value }) +Link // asp-route-* for query strings +``` + +### [Select Tag Helper](https://docs.microsoft.com/en-us/aspnet/core/mvc/views/working-with-forms) + +[StackOverflow](https://stackoverflow.com/a/34624217) +[SelectList Docs](https://docs.microsoft.com/en-us/dotnet/api/system.web.mvc.selectlist) + +In `ViewModel.cs`: + +```cs +class ViewModel +{ + public int EntityId { get; set; } // value selected in form ends up here + + // object has numeric id and other props + public SelectList Entities = new() + + public ViewModel(){ } // parameterless constructor (NEEDED) +} +``` + +In `View.cs` + +```cs +@model ViewModel + +

+ + + +