PM> install-package EntityFrameworkWithHierarchyId

public class Employee
{
    public int Id { get; set; }
 
    [Required, MaxLength(100)]
    public string Name { get; set; }
 
    [Required]
    public HierarchyId Node { get; set; } // نوع داده جدید
}

public class MyContext : DbContext
{
    public DbSet<Employee> Employees { get; set; }
 
    public MyContext()
        : base("Connection1")
    {
        this.Database.Log = log => Console.WriteLine(log);
    }
}
 
public class Configuration : DbMigrationsConfiguration<MyContext>
{
    public Configuration()
    {
        AutomaticMigrationsEnabled = true;
        AutomaticMigrationDataLossAllowed = true;
    }
 
    protected override void Seed(MyContext context)
    {
        if (context.Employees.Any())
            return;
 
        context.Database.ExecuteSqlCommand(
            "ALTER TABLE [dbo].[Employees] ADD NodePath as Node.ToString() persisted");
        context.Database.ExecuteSqlCommand(
            "ALTER TABLE [dbo].[Employees] ADD Level AS Node.GetLevel() persisted");
        context.Database.ExecuteSqlCommand(
            "ALTER TABLE [dbo].[Employees] ADD ManagerNode as Node.GetAncestor(1) persisted");
        context.Database.ExecuteSqlCommand(
            "ALTER TABLE [dbo].[Employees] ADD ManagerNodePath as Node.GetAncestor(1).ToString() persisted");
 
        context.Database.ExecuteSqlCommand(
            "ALTER TABLE [dbo].[Employees] ADD CONSTRAINT [UK_EmployeeNode] UNIQUE NONCLUSTERED (Node)");
        context.Database.ExecuteSqlCommand(
            "ALTER TABLE [dbo].[Employees]  WITH CHECK ADD CONSTRAINT [EmployeeManagerNodeNodeFK] " +
            "FOREIGN KEY([ManagerNode]) REFERENCES [dbo].[Employees] ([Node])");
 
        context.Employees.Add(new Employee { Name = "Root", Node = new HierarchyId("/") });
        context.Employees.Add(new Employee { Name = "Emp1", Node = new HierarchyId("/1/") });
        context.Employees.Add(new Employee { Name = "Emp2", Node = new HierarchyId("/2/") });
        context.Employees.Add(new Employee { Name = "Emp3", Node = new HierarchyId("/1/1/") });
        context.Employees.Add(new Employee { Name = "Emp4", Node = new HierarchyId("/1/1/1/") });
        context.Employees.Add(new Employee { Name = "Emp5", Node = new HierarchyId("/2/1/") });
        context.Employees.Add(new Employee { Name = "Emp6", Node = new HierarchyId("/1/2/") });
 
        base.Seed(context);
    }
}

using (var context = new MyContext())
{
    Console.WriteLine("\ngetItems OrderByDescending(employee => employee.Node)");
 
    var employees = context.Employees.OrderByDescending(employee => employee.Node).ToList();
    foreach (var employee in employees)
    {
        Console.WriteLine("{0} {1}", employee.Id, employee.Node);
    }
 }

SELECT
    [Extent1].[Id] AS [Id],
    [Extent1].[Name] AS [Name],
    [Extent1].[Node] AS [Node]
    FROM [dbo].[Employees] AS [Extent1]
    ORDER BY [Extent1].[Node] DESC


6 /2/1/
3 /2/
7 /1/2/
5 /1/1/1/
4 /1/1/
2 /1/
1 /

using (var context = new MyContext())
{
    Console.WriteLine("\nGetAncestor(1) of /1/");
 
    var firstItem = context.Employees.Single(employee => employee.Node == new HierarchyId("/1/"));
    foreach (var item in context.Employees.Where(employee => firstItem.Node == employee.Node.GetAncestor(1)))
    {
        Console.WriteLine("{0} {1}", item.Id, item.Name);
    }
}

SELECT TOP (2)
    [Extent1].[Id] AS [Id],
    [Extent1].[Name] AS [Name],
    [Extent1].[Node] AS [Node]
    FROM [dbo].[Employees] AS [Extent1]
    WHERE cast('/1/' as hierarchyid) = [Extent1].[Node]

SELECT
    [Extent1].[Id] AS [Id],
    [Extent1].[Name] AS [Name],
    [Extent1].[Node] AS [Node]
    FROM [dbo].[Employees] AS [Extent1]
    WHERE (@p__linq__0 = ([Extent1].[Node].GetAncestor(1))) OR ((@p__linq__0 IS
NULL) AND ([Extent1].[Node].GetAncestor(1) IS NULL))
-- p__linq__0: '/1/' (Type = Object)

4 Emp3
7 Emp6

var list = context.Employees.Where(
          employee => employee.Node.IsDescendantOf(new HierarchyId("/1/")) &&
                              employee.Node.GetLevel() == 2).ToList();

SELECT
    [Extent1].[Id] AS [Id],
    [Extent1].[Name] AS [Name],
    [Extent1].[Node] AS [Node]
    FROM [dbo].[Employees] AS [Extent1]
    WHERE (([Extent1].[Node].IsDescendantOf(cast('/1/' as hierarchyid))) = 1) 
    AND (2 = ([Extent1].[Node].GetLevel()))

var items = context.Employees.Where(employee => employee.Node.IsDescendantOf(new HierarchyId("/1/")))
    .Select(employee => new
    {
        Id = employee.Id,
        OrigPath = employee.Node,
        ReparentedValue = employee.Node.GetReparentedValue(new HierarchyId("/1/"), HierarchyId.GetRoot()),
        Level = employee.Node.GetLevel()
    }).ToList();
 
foreach (var item in items)
{
    Console.WriteLine("Id:{0}; OrigPath:{1}; ReparentedValue:{2}; Level:{3}", item.Id, item.OrigPath, item.ReparentedValue, item.Level);
}

SELECT
    [Extent1].[Id] AS [Id],
    [Extent1].[Node] AS [Node],
    [Extent1].[Node].GetReparentedValue(cast('/1/' as hierarchyid), hierarchyid::GetRoot()) AS [C1],
    [Extent1].[Node].GetLevel() AS [C2]
    FROM [dbo].[Employees] AS [Extent1]
    WHERE ([Extent1].[Node].IsDescendantOf(cast('/1/' as hierarchyid))) = 1


Id:2; OrigPath:/1/; ReparentedValue:/; Level:1
Id:4; OrigPath:/1/1/; ReparentedValue:/1/; Level:2
Id:5; OrigPath:/1/1/1/; ReparentedValue:/1/1/; Level:3
Id:7; OrigPath:/1/2/; ReparentedValue:/2/; Level:2

<li>Item 1</li>
<li>Item 2</li>

<li>Item 1</li>
<li>Item 2</li>
<li>Item 3</li>

<li>Item 0</li> // <= New item
<li>Item 1</li>
<li>Item 2</li>
<li>Item 3</li>

<li key={0}>Item 0</li> // <= New item
<li key={1}>Item 1</li>
<li key={2}>Item 2</li>
<li key={3}>Item 3</li>

@page "/"

<button class="btn btn-primary" @onclick="addPerson">Add Person</button>

<ul class="mt-5">
    @foreach (var person in People)
    {
        <li>@person.Id, @person.Name</li>
    }
</ul>

@code{

    List<Person> People = new()
    {
        new() { Id = 1, Name = "User 1" },
        new() { Id = 2, Name = "User 2" },
    };
    int LastId = 2;

    void addPerson()
    {
        People.Insert(0, new() { Id = ++LastId, Name = $"User {LastId}" });
    }

    class Person
    {
        public int Id { set; get; }
        public string Name { set; get; }
    }
}

<ul class="mt-5">
    @foreach (var person in People)
    {
        <li @key="person.Id">@person.Id, @person.Name</li>
    }
</ul>

//Console.WriteLine("====Parent====");
//Parent parent = new Parent();
//parent.Print();

//Console.WriteLine("====Child====");
//Child child = new Child();
//child.Print();

Console.WriteLine("====Parent Via Child====");
Parent pc = new Child();
pc.Print();

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>

    <link href="Content/font-awesome.css" rel="stylesheet" />
    <link href="Content/froala_editor.css" rel="stylesheet" />

    <script src="Scripts/jquery-1.10.2.min.js"></script>
    <script src="Scripts/froala_editor.min.js"></script>
    <script src="Scripts/langs/fa.js"></script>
</head>
<body>
    <form id="form1" runat="server">
    </form>
</body>
</html>

@{
    ViewBag.Title = "Index";
}

<style type="text/css">
    /*تنظیم فونت پیش فرض ادیتور*/
    .froala-element {
    }
</style>

@using (Html.BeginForm(actionName: "Index", controllerName: "Home"))
{
    @Html.TextArea(name: "Editor1")
    <input type="submit" value="ارسال" />
}

@section Scripts
{
    <script type="text/javascript">
        $(function () {
            $('#Editor1').editable({
                buttons: ["bold", "italic", "underline", "strikeThrough", "fontFamily",
                    "fontSize", "color", "formatBlock", "align", "insertOrderedList",
                    "insertUnorderedList", "outdent", "indent", "selectAll", "createLink",
                    "insertImage", "insertVideo", "undo", "redo", "html", "save", "inserthorizontalrule"],
                inlineMode: false,
                inverseSkin: true,
                preloaderSrc: '@Url.Content("~/Content/img/preloader.gif")',
                allowedImageTypes: ["jpeg", "jpg", "png"],
                height: 300,
                language: "fa",
                direction: "rtl",
                fontList: ["Tahoma, Geneva", "Arial, Helvetica", "Impact, Charcoal"],
                autosave: true,
                autosaveInterval: 2500,
                saveURL: '@Url.Action("FroalaAutoSave", "Home")',
                saveParams: { postId: "123" },
                spellcheck: true,
                plainPaste: true,
                imageButtons: ["removeImage", "replaceImage", "linkImage"],
                borderColor: '#00008b',
                imageUploadURL: '@Url.Action("FroalaUploadImage", "Home")',
                imageParams: { postId: "123" },
                enableScript: false
            });
        });
    </script>
}

        /// <summary>
        /// ذخیره سازی خودکار
        /// </summary>
        [HttpPost]
        [ValidateInput(false)]
        public ActionResult FroalaAutoSave(string body, int? postId) // نام پارامتر بادی را تغییر ندهید
        {
            //todo: save body ...
            return new EmptyResult();
        }

        // todo: مسایل امنیتی آپلود را فراموش نکنید
        /// <summary>
        /// ذخیره سازی تصاویر ارسالی
        /// </summary>
        [HttpPost]
        public ActionResult FroalaUploadImage(HttpPostedFileBase file, int? postId) // نام پارامتر فایل را تغییر ندهید
        {
            var fileName = Path.GetFileName(file.FileName);
            var rootPath = Server.MapPath("~/images/");
            file.SaveAs(Path.Combine(rootPath, fileName));
            return Json(new { link = "images/" + fileName }, JsonRequestBehavior.AllowGet);
        }

<%@ Page Title="" Language="C#" MasterPageFile="~/Site.Master"
    ValidateRequest="false"
    EnableEventValidation="false"
    AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="FroalaWebFormsTest.Default" %>

<%--اعتبارسنجی ورودی غیرفعال شده چون باید تگ ارسال شود--%>
<%--همچنین در وب کانفیگ هم تنظیم دیگری نیاز دارد--%>

<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
    <%--حالت کلاینت آی دی بهتر است تنظیم شود در اینجا--%>
    <asp:TextBox ID="txtEditor" ClientIDMode="Static"
        runat="server" Height="199px" TextMode="MultiLine" Width="447px"></asp:TextBox>
    <br />
    <asp:Button ID="btnSave" runat="server" OnClick="btnSave_Click" Text="ارسال" />

    <style type="text/css">
        /*تنظیم فونت پیش فرض ادیتور*/
        .froala-element {
        }
    </style>

    <script type="text/javascript">
        $(function () {
            $('#txtEditor').editable({
                buttons: ["bold", "italic", "underline", "strikeThrough", "fontFamily",
                    "fontSize", "color", "formatBlock", "align", "insertOrderedList",
                    "insertUnorderedList", "outdent", "indent", "selectAll", "createLink",
                    "insertImage", "insertVideo", "undo", "redo", "html", "save", "inserthorizontalrule"],
                inlineMode: false,
                inverseSkin: true,
                preloaderSrc: 'Content/img/preloader.gif',
                allowedImageTypes: ["jpeg", "jpg", "png"],
                height: 300,
                language: "fa",
                direction: "rtl",
                fontList: ["Tahoma, Geneva", "Arial, Helvetica", "Impact, Charcoal"],
                autosave: true,
                autosaveInterval: 2500,
                saveURL: 'FroalaHandler.ashx',
                saveParams: { postId: "123" },
                spellcheck: true,
                plainPaste: true,
                imageButtons: ["removeImage", "replaceImage", "linkImage"],
                borderColor: '#00008b',
                imageUploadURL: 'FroalaHandler.ashx',
                imageParams: { postId: "123" },
                enableScript: false
            });
        });
    </script>
</asp:Content>

using System.IO;
using System.Web;
using System.Web.Script.Serialization;

namespace FroalaWebFormsTest
{
    public class FroalaHandler : IHttpHandler
    {
        //todo: برای اینکارها بهتر است از وب ای پی آی استفاده شود
        //todo: یا دو هندلر مجزا یکی برای تصاویر و دیگری برای ذخیره سازی متن

        public void ProcessRequest(HttpContext context)
        {
            var body = context.Request.Form["body"];
            var postId = context.Request.Form["postId"];
            if (!string.IsNullOrWhiteSpace(body) && !string.IsNullOrWhiteSpace(postId))
            {
                //todo: save changes

                context.Response.ContentType = "text/plain";
                context.Response.Write("");
                context.Response.End();
            }

            var files = context.Request.Files;
            if (files.Keys.Count > 0)
            {
                foreach (string fileKey in files)
                {
                    var file = context.Request.Files[fileKey];
                    if (file == null || file.ContentLength == 0)
                        continue;

                    //todo: در اینجا مسایل امنیتی آپلود فراموش نشود
                    var fileName = Path.GetFileName(file.FileName);
                    var rootPath = context.Server.MapPath("~/images/");
                    file.SaveAs(Path.Combine(rootPath, fileName));


                    var json = new JavaScriptSerializer().Serialize(new { link = "images/" + fileName });
                    // البته اینجا یک فایل بیشتر ارسال نمی‌شود
                    context.Response.ContentType = "text/plain";
                    context.Response.Write(json);
                    context.Response.End();
                }
            }

            context.Response.ContentType = "text/plain";
            context.Response.Write("");
            context.Response.End();
        }

        public bool IsReusable
        {
            get { return false; }
        }
    }
}

<location path="upload">
  <system.webServer>
    <handlers accessPolicy="Read" />
  </system.webServer>
</location>

declare @t table
(id char(1) primary key,
parent char(1));
 
insert @t values
('A',null),                                   --Level 1
('B', 'A'), ('C', 'A'),                       --Level 2
('D', 'B'), ('E', 'B'),('R','B'), ('F', 'C'), --Level 3
('G', 'D'),                                   --Level 4
('H', 'G'), ('I', 'G');                       --Level 5

;with cte as
(
select id, rnk=0, 
       concats = cast(id as varchar(10))
from @t
where parent is null
 
union all
 
select t.id, rnk+1,
       cast(cte.concats + t.id as varchar(10))
from cte join @t t
on cte.id = t.parent
)
select * from cte
/*
id   rnk         concats
---- ----------- ----------
A    0           A
B    1           AB
C    1           AC
F    2           ACF
D    2           ABD
E    2           ABE
R    2           ABR
G    3           ABDG
H    4           ABDGH
I    4           ABDGI
*/
;with cte as
(
select id, rnk=0, 
       concats = cast(id as varchar(10))
from @t
where parent is null
 
union all
 
select t.id, rnk+1,
       cast(cte.concats + t.id as varchar(10))
from cte join @t t
on cte.id = t.parent
)
select stuff(d.list,1,1,'') as concats
from (select ','+concats
      from cte
  for xml path(''))d(list)
/*
concats
----------------------------------------
A,AB,AC,ACF,ABD,ABE,ABR,ABDG,ABDGH,ABDGI
*/

using System.Windows;
using StructureMap;

namespace WpfFramework1999.Common.MVVM
{
    /// <summary>
    /// Stitches together a view and its view-model
    /// </summary>
    public class ViewModelFactory
    {
        private readonly FrameworkElement _control;

        /// <summary>
        /// سازنده کلاس تزریق وابستگی‌ها به ویوو مدل و وهله سازی آن
        /// </summary>
        /// <param name="control">وهله‌ای از شیءایی که باید کار تزریق وابستگی‌ها در آن انجام شود</param>
        public ViewModelFactory(FrameworkElement control)
        {
            _control = control;
        }

        /// <summary>
        /// وهله متناظر با ویوو مدل
        /// </summary>
        public IViewModel ViewModelInstance { get; private set; }

        /// <summary>
        /// کار تزریق خودکار وابستگی‌ها و وهله سازی ویوو مدل مرتبط انجام خواهد شد
        /// </summary>        
        public void WireUp()
        {
            var viewName = _control.GetType().Name;
            var viewModelName = string.Concat(viewName, "ViewModel"); //قرار داد نامگذاری ما است

            if (!_control.IsLoaded)
            {
                _control.Loaded += (s, e) =>
                {
                    setDataContext(viewModelName);
                };
            }
            else
            {
                setDataContext(viewModelName);
            }
        }

        private void setDataContext(string viewModelName)
        {
            //کار تزریق خودکار وابستگی‌ها و وهله سازی ویوو مدل مرتبط انجام خواهد شد
            ViewModelInstance = ObjectFactory.TryGetInstance<IViewModel>(viewModelName);
            if (ViewModelInstance == null) // این صفحه ویوو مدل ندارد
                return;

            _control.DataContext = ViewModelInstance;
        }
    }
}

/// <summary>
/// ویوو مدل افزودن و مدیریت کاربران
/// </summary>
public class AddNewUserViewModel : BaseViewModel

/// <summary>
/// کلاس پایه ویوو مدل‌های برنامه که جهت علامتگذاری آن‌ها برای سیم کشی‌های تزریق وابستگی‌های برنامه نیز استفاده می‌شود
/// </summary>
public abstract class BaseViewModel : DataErrorInfoBase, INotifyPropertyChanged, IViewModel

// Add all types that implement IView into the container,
// and name each specific type by the short type name.
scan.AddAllTypesOf<IViewModel>().NameBy(type => type.Name);

 //کار تزریق خودکار وابستگی‌ها و وهله سازی ویوو مدل مرتبط انجام خواهد شد
ViewModelInstance = ObjectFactory.TryGetInstance<IViewModel>(viewModelName);

namespace WpfFramework.Infrastructure.Core
{
    /// <summary>
    /// ایجاد یک کنترل فریم سفارشی که قابلیت تزریق وابستگی‌ها را به صورت خودکار دارد
    /// به همراه اعمال مسایل راهبری برنامه که از منوی اصلی دریافت می‌شوند
    /// </summary>
    public class FrameFactory : Frame
    {
        /// <summary>
        /// در اینجا می‌شود به وهله‌ای از صفحه‌ای که قرار است اضافه گردد دسترسی یافت
        /// </summary>
        protected override void OnContentChanged(object oldContent, object newContent)
        {
            base.OnContentChanged(oldContent, newContent);

            var newPage = newContent as FrameworkElement;
            if (newPage == null)
                return;

            _currentViewModelFactory = new ViewModelFactory(newPage);
            _currentViewModelFactory.WireUp(); //کار تزریق وابستگی‌ها و وهله سازی ویوو مدل مرتبط انجام خواهد شد
        }
    }
}

//dynamic reflection
PropertyInfo property = typeof (MyClass).GetProperty("Name");
MethodInfo method = typeof (MyClass).GetMethod("SomeMethod");

public string TextBoxFor<T>(Expression<Func<T,object>> expression);

<%= this.TextBoxFor(model => model.FirstName); %>

public PropertyInfo GetProperty<T>(Expression<Func<T, object>> expression)
{
 var memberExpression = expression.Body as MemberExpression;

 if (memberExpression == null)
     throw new InvalidOperationException("Not a member access.");

  return memberExpression.Member as PropertyInfo;
}

public class AddressMap : DomainMap<Address>
{
 public AddressMap()
 {
    Map(a => a.Address1);
 }
}

• Expression Tree Basics

• Functional Programming for Everyday .NET Development

• Introduction to static reflection

• The basics behind static reflection

• Dynamic reflection versus static reflection

• Static Reflection of property names

• Lisp is sin

Here are some of the reasons why nullable reference types are less than ideal:

• Invoking a member on a null value will issue a System.NullReferenceException exception, and every invocation that results in a System.NullReferenceException in production code is a bug. Unfortunately, however, with nullable reference types we “fall in” to doing the wrong thing rather than the right thing. The “fall in” action is to invoke a reference type without checking for null.
• There’s an inconsistency between reference types and value types (following the introduction of Nullable<T>) in that value types are nullable when decorated with  “?” (for example, int? number); otherwise, they default to non-nullable. In contrast, reference types are nullable by default. This is “normal” to those of us who have been programming in C# for a long time, but if we could do it all over, we’d want the default for reference types to be non-nullable and the addition of a “?” to be an explicit way to allow nulls.
• It’s not possible to run static flow analysis to check all paths regarding whether a value will be null before dereferencing it, or not. Consider, for example, if there were unmanaged code invocations, multi-threading, or null assignment/­replacement based on runtime conditions. (Not to mention whether analysis would include checking of all library APIs that are invoked.)
• There’s no reasonable syntax to indicate that a reference type value of null is invalid for a particular declaration.
• There’s no way to decorate parameters to not allow null.