Setup Mkdocs (#7)

* Compile docs with Mkdocs

* Add info about project

docs/dotnet/asp.net/razor-pages.md

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+# 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 entry-point
+|- 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 <title>Page Title</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() { }
+    }
+}
+```
+
+## 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 DBContext through DI
+        public IndexModel(ApplicationDbContext db)
+        {
+            _db = db;
+        }
+
+        [BindProperty]  // assumed to be received on POST
+        public IEnumerable<Entity> Entities { get; set; }
+
+        // HTTP Method Handler
+        public async Task OnGet()
+        {   
+            // get data from DB (example operation)
+            Entities = await _db.Entities.ToListAsync();
+        }
+
+        // HTTP Method Handler
+        public async Task<IActionResult> 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 entry-point and default document (missing file in URL redirects to index)
+
+| URL                    | Maps TO                                            |
+|------------------------|----------------------------------------------------|
+| www.domain.com         | /Pages/Index.cshtml                                |
+| www.domain.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
+<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 displayed 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 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<IActionResult> OnPost()
+        {
+            if (ModelState.IsValid)
+            {
+
+                await _db.SaveChangesAsync();
+
+                return RedirectToPage("Index");
+            }
+            else
+            {
+                return Page();
+            }
+        }
+    }
+}
+```