public class DebuggerBrowsableTest
{
    [DebuggerBrowsable(DebuggerBrowsableState.Never)] // عدم نمایش در زمان دیباگ در پنجره متغیرها
    public string FirstName { get; set; }

    [DebuggerBrowsable(DebuggerBrowsableState.Collapsed)] // مقدار پیش فرض
    public string LastName { get; set; }

    [DebuggerBrowsable( DebuggerBrowsableState.RootHidden )] // عدم نمایش در زمان دیباگ در پنجره متغیرها
    public string FullName => FirstName + " " + LastName;

    [DebuggerBrowsable( DebuggerBrowsableState.RootHidden )] // تنها در زمانی که یک آرایه یا لیست باشد نمایش داده می‌شود
    public string[] FullNameArray => new string[] { FirstName + " " + LastName };
}

Operator ??

عملگر ??  در صورتی که عملوند سمت چپ آن تهی (null) نباشد، مقدار آن را باز می‌گرداند و در غیر اینصورت مقدار عملوند سمت راست خود را باز می‌گرداند. نوع‌های تهی پذیر (nullable) می‌توانند دارای مقدار و یا به صورت تعریف نشده باشند. عملگر ?? وقتی که یک نوع تهی پذیر به یک نوع غیرتهی پذیر انتساب داده می‌شود، مقدار پیش فرض آن را باز می‌گرداند.

int? x = null;
int y = x ?? -1;
Console.WriteLine("y now equals -1 because x was null => {0}", y);
int i = DefaultValueOperatorTest.GetNullableInt() ?? default(int);
Console.WriteLine("i equals now 0 because GetNullableInt() returned null => {0}", i);
string s = DefaultValueOperatorTest.GetStringValue();
Console.WriteLine("Returns 'Unspecified' because s is null => {0}", s ?? "Unspecified");

    public class User
    {
        public User()
        {
            UserRoles = new HashSet<UserRole>();
        }

        public int Id { get; set; }

        public string Username { get; set; }

        public string Password { get; set; }

        public string DisplayName { get; set; }

        public bool IsActive { get; set; }

        public DateTimeOffset? LastLoggedIn { get; set; }

        /// <summary>
        /// every time the user changes his Password,
        /// or an admin changes his Roles or stat/IsActive,
        /// create a new `SerialNumber` GUID and store it in the DB.
        /// </summary>
        public string SerialNumber { get; set; }

        public virtual ICollection<UserRole> UserRoles { get; set; }
    }

    public class Role
    {
        public Role()
        {
            UserRoles = new HashSet<UserRole>();
        }

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

        public virtual ICollection<UserRole> UserRoles { get; set; }
    }

    public static class CustomRoles
    {
        public const string Admin = nameof(Admin);
        public const string User = nameof(User);
    }

    public class UserRole
    {
        public int UserId { get; set; }
        public int RoleId { get; set; }

        public virtual User User { get; set; }
        public virtual Role Role { get; set; }
    }

    public interface IUnitOfWork : IDisposable
    {
        DbSet<TEntity> Set<TEntity>() where TEntity : class;

        int SaveChanges(bool acceptAllChangesOnSuccess);
        int SaveChanges();
        Task<int> SaveChangesAsync(bool acceptAllChangesOnSuccess, CancellationToken cancellationToken = new CancellationToken());
        Task<int> SaveChangesAsync(CancellationToken cancellationToken = new CancellationToken());
    }

    public class ApplicationDbContext : DbContext, IUnitOfWork
    {
        public ApplicationDbContext(DbContextOptions options) : base(options)
        { }

        public virtual DbSet<User> Users { set; get; }
        public virtual DbSet<Role> Roles { set; get; }
        public virtual DbSet<UserRole> UserRoles { get; set; }

        protected override void OnModelCreating(ModelBuilder builder)
        {
            // it should be placed here, otherwise it will rewrite the following settings!
            base.OnModelCreating(builder);

            // Custom application mappings
            builder.Entity<User>(entity =>
            {
                entity.Property(e => e.Username).HasMaxLength(450).IsRequired();
                entity.HasIndex(e => e.Username).IsUnique();
                entity.Property(e => e.Password).IsRequired();
                entity.Property(e => e.SerialNumber).HasMaxLength(450);
            });

            builder.Entity<Role>(entity =>
            {
                entity.Property(e => e.Name).HasMaxLength(450).IsRequired();
                entity.HasIndex(e => e.Name).IsUnique();
            });

            builder.Entity<UserRole>(entity =>
            {
                entity.HasKey(e => new { e.UserId, e.RoleId });
                entity.HasIndex(e => e.UserId);
                entity.HasIndex(e => e.RoleId);
                entity.Property(e => e.UserId);
                entity.Property(e => e.RoleId);
                entity.HasOne(d => d.Role).WithMany(p => p.UserRoles).HasForeignKey(d => d.RoleId);
                entity.HasOne(d => d.User).WithMany(p => p.UserRoles).HasForeignKey(d => d.UserId);
            });
        }
    }

    /// <summary>
    /// Only used by EF Tooling
    /// </summary>
    public class ApplicationDbContextFactory : IDesignTimeDbContextFactory<ApplicationDbContext>
    {
        public ApplicationDbContext CreateDbContext(string[] args)
        {
            var basePath = Directory.GetCurrentDirectory();
            Console.WriteLine($"Using `{basePath}` as the BasePath");
            var configuration = new ConfigurationBuilder()
                                    .SetBasePath(basePath)
                                    .AddJsonFile("appsettings.json")
                                    .Build();
            var builder = new DbContextOptionsBuilder<ApplicationDbContext>();
            var connectionString = configuration.GetConnectionString("DefaultConnection");
            builder.UseSqlServer(connectionString);
            return new ApplicationDbContext(builder.Options);
        }
    }

{
  "ConnectionStrings": {
    "DefaultConnection": "Data Source=(LocalDB)\\MSSQLLocalDB;Initial Catalog=ASPNETCore2CookieAuthenticationDB;Integrated Security=True;MultipleActiveResultSets=True;"
  },
  "LoginCookieExpirationDays": 30
}

    public interface IUsersService
    {
        Task<string> GetSerialNumberAsync(int userId);
        Task<User> FindUserAsync(string username, string password);
        Task<User> FindUserAsync(int userId);
        Task UpdateUserLastActivityDateAsync(int userId);
    }

    public interface IRolesService
    {
        Task<List<Role>> FindUserRolesAsync(int userId);
        Task<bool> IsUserInRole(int userId, string roleName);
        Task<List<User>> FindUsersInRoleAsync(string roleName);
    }

    public interface IDbInitializerService
    {
        void Initialize();
        void SeedData();
    }

    public interface ICookieValidatorService
    {
        Task ValidateAsync(CookieValidatePrincipalContext context);
    }

    public class CookieValidatorService : ICookieValidatorService
    {
        private readonly IUsersService _usersService;
        public CookieValidatorService(IUsersService usersService)
        {
            _usersService = usersService;
            _usersService.CheckArgumentIsNull(nameof(usersService));
        }

        public async Task ValidateAsync(CookieValidatePrincipalContext context)
        {
            var userPrincipal = context.Principal;

            var claimsIdentity = context.Principal.Identity as ClaimsIdentity;
            if (claimsIdentity?.Claims == null || !claimsIdentity.Claims.Any())
            {
                // this is not our issued cookie
                await handleUnauthorizedRequest(context);
                return;
            }

            var serialNumberClaim = claimsIdentity.FindFirst(ClaimTypes.SerialNumber);
            if (serialNumberClaim == null)
            {
                // this is not our issued cookie
                await handleUnauthorizedRequest(context);
                return;
            }

            var userIdString = claimsIdentity.FindFirst(ClaimTypes.UserData).Value;
            if (!int.TryParse(userIdString, out int userId))
            {
                // this is not our issued cookie
                await handleUnauthorizedRequest(context);
                return;
            }

            var user = await _usersService.FindUserAsync(userId).ConfigureAwait(false);
            if (user == null || user.SerialNumber != serialNumberClaim.Value || !user.IsActive)
            {
                // user has changed his/her password/roles/stat/IsActive
                await handleUnauthorizedRequest(context);
            }

            await _usersService.UpdateUserLastActivityDateAsync(userId).ConfigureAwait(false);
        }

        private Task handleUnauthorizedRequest(CookieValidatePrincipalContext context)
        {
            context.RejectPrincipal();
            return context.HttpContext.SignOutAsync(CookieAuthenticationDefaults.AuthenticationScheme);
        }
    }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddScoped<IUnitOfWork, ApplicationDbContext>();
            services.AddScoped<IUsersService, UsersService>();
            services.AddScoped<IRolesService, RolesService>();
            services.AddScoped<ISecurityService, SecurityService>();
            services.AddScoped<ICookieValidatorService, CookieValidatorService>();
            services.AddScoped<IDbInitializerService, DbInitializerService>();

            services.AddDbContext<ApplicationDbContext>(options =>
            {
                options.UseSqlServer(
                    Configuration.GetConnectionString("DefaultConnection"),
                    serverDbContextOptionsBuilder =>
                        {
                            var minutes = (int)TimeSpan.FromMinutes(3).TotalSeconds;
                            serverDbContextOptionsBuilder.CommandTimeout(minutes);
                            serverDbContextOptionsBuilder.EnableRetryOnFailure();
                        });
            });

            // Only needed for custom roles.
            services.AddAuthorization(options =>
                    {
                        options.AddPolicy(CustomRoles.Admin, policy => policy.RequireRole(CustomRoles.Admin));
                        options.AddPolicy(CustomRoles.User, policy => policy.RequireRole(CustomRoles.User));
                    });

            // Needed for cookie auth.
            services
                .AddAuthentication(options =>
                {
                    options.DefaultChallengeScheme = CookieAuthenticationDefaults.AuthenticationScheme;
                    options.DefaultSignInScheme = CookieAuthenticationDefaults.AuthenticationScheme;
                    options.DefaultAuthenticateScheme = CookieAuthenticationDefaults.AuthenticationScheme;
                })
                .AddCookie(options =>
                {
                    options.SlidingExpiration = false;
                    options.LoginPath = "/api/account/login";
                    options.LogoutPath = "/api/account/logout";
                    //options.AccessDeniedPath = new PathString("/Home/Forbidden/");
                    options.Cookie.Name = ".my.app1.cookie";
                    options.Cookie.HttpOnly = true;
                    options.Cookie.SecurePolicy = CookieSecurePolicy.SameAsRequest;
                    options.Cookie.SameSite = SameSiteMode.Lax;
                    options.Events = new CookieAuthenticationEvents
                    {
                        OnValidatePrincipal = context =>
                        {
                            var cookieValidatorService = context.HttpContext.RequestServices.GetRequiredService<ICookieValidatorService>();
                            return cookieValidatorService.ValidateAsync(context);
                        }
                    };
                });

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
   app.UseAuthentication();

            var scopeFactory = app.ApplicationServices.GetRequiredService<IServiceScopeFactory>();
            using (var scope = scopeFactory.CreateScope())
            {
                var dbInitializer = scope.ServiceProvider.GetService<IDbInitializerService>();
                dbInitializer.Initialize();
                dbInitializer.SeedData();
            }

        [AllowAnonymous]
        [HttpPost("[action]")]
        public async Task<IActionResult> Login([FromBody]  User loginUser)
        {
            if (loginUser == null)
            {
                return BadRequest("user is not set.");
            }

            var user = await _usersService.FindUserAsync(loginUser.Username, loginUser.Password).ConfigureAwait(false);
            if (user == null || !user.IsActive)
            {
                await HttpContext.SignOutAsync(CookieAuthenticationDefaults.AuthenticationScheme);
                return Unauthorized();
            }

            var loginCookieExpirationDays = _configuration.GetValue<int>("LoginCookieExpirationDays", defaultValue: 30);
            var cookieClaims = await createCookieClaimsAsync(user).ConfigureAwait(false);
            await HttpContext.SignInAsync(
                CookieAuthenticationDefaults.AuthenticationScheme,
                cookieClaims,
                new AuthenticationProperties
                {
                    IsPersistent = true, // "Remember Me"
                    IssuedUtc = DateTimeOffset.UtcNow,
                    ExpiresUtc = DateTimeOffset.UtcNow.AddDays(loginCookieExpirationDays)
                });

            await _usersService.UpdateUserLastActivityDateAsync(user.Id).ConfigureAwait(false);

            return Ok();
        }

        private async Task<ClaimsPrincipal> createCookieClaimsAsync(User user)
        {
            var identity = new ClaimsIdentity(CookieAuthenticationDefaults.AuthenticationScheme);
            identity.AddClaim(new Claim(ClaimTypes.NameIdentifier, user.Id.ToString()));
            identity.AddClaim(new Claim(ClaimTypes.Name, user.Username));
            identity.AddClaim(new Claim("DisplayName", user.DisplayName));

            // to invalidate the cookie
            identity.AddClaim(new Claim(ClaimTypes.SerialNumber, user.SerialNumber));

            // custom data
            identity.AddClaim(new Claim(ClaimTypes.UserData, user.Id.ToString()));

            // add roles
            var roles = await _rolesService.FindUserRolesAsync(user.Id).ConfigureAwait(false);
            foreach (var role in roles)
            {
                identity.AddClaim(new Claim(ClaimTypes.Role, role.Name));
            }

            return new ClaimsPrincipal(identity);
        }

[Route("api/[controller]")]
[Authorize(Policy = CustomRoles.Admin)]
public class MyProtectedAdminApiController : Controller

        [AllowAnonymous]
        [HttpGet("[action]"), HttpPost("[action]")]
        public async Task<bool> Logout()
        {
            await HttpContext.SignOutAsync(CookieAuthenticationDefaults.AuthenticationScheme);
            return true;
        }

public struct Statement
{
    public int Id { get; }
    public string Description { get; }
    public Statement(int id, string description) => (Id, Description) = (id, description);
    public override string ToString() => Description;
}

public static async Task<IEnumerable<Statement>> GetStatements(bool error)
{
    if (error)
    {
       throw new Exception("Oops, we messed up 😬");
    }

    await Task.Delay(1000); //Simulate waiting for data to come through. 

    yield return new Statement(1, "C# is cool!");
    yield return new Statement(2, "C# orginally named COOL.");
    yield return new Statement(3, "More examples...");
}

The body of 'AsyncStreams.GetStatements(bool)' cannot be an iterator block because
'Task<IEnumerable<AsyncStreams.Statement>>' is not an iterator interface type (CS1624)

static async IAsyncEnumerable<Statement> GetStatements(bool error)

static async IAsyncEnumerable<Statement> GetStatementsAsync(bool error)
{
    await foreach (var statement in GetStatements(error))
    {
      await Task.Delay(1000);
      yield return statement;
    }
}

using System.Threading;

namespace System.Collections.Generic
{
    public interface IAsyncEnumerable<out T>
    {
        IAsyncEnumerator<T> GetAsyncEnumerator(CancellationToken cancellationToken = default);
    }

    public interface IAsyncEnumerator<out T> : IAsyncDisposable
    {
        T Current { get; }

        ValueTask<bool> MoveNextAsync();
    }
}

namespace System
{
    public interface IAsyncDisposable
    {
        ValueTask DisposeAsync();
    }
}

public class AwaitUsingTest : IAsyncDisposable
{
   public async ValueTask DisposeAsync()
   {
     await Task.CompletedTask;
   }

   public void Dummy() { }
}

async Task FooBar()
{
   await using var test = new AwaitUsingTest();
   test.Dummy();
}

class Player
{
   public string Name;
   public int Age;
   public void Walk()
   {
      // کدهای مربوط به پیاده سازی راه رفتن
   }
   public void Run()
   {
      // کدهای مربوط به پیاده سازی دویدن
   }
}

Player objPlayer = new Player();
objPlayer.Name = “Ali Karimi”;
objPlayer.Age = 30;
objPlayer.Run();

1. روش JSON-LD
2. روش Microdata
3. روش RDFa

using System;
using System.Data.Entity;
using System.Data.Entity.Migrations;

namespace TestKeys
{
    public class Bill
    {
        public int Id { get; set; }
        public decimal Amount { set; get; }
        public virtual Account Account { get; set; }
    }

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

    public class MyContext : DbContext
    {
        public DbSet<Bill> Bills { get; set; }
        public DbSet<Account> Accounts { get; set; }
    }

    public class Configuration : DbMigrationsConfiguration<MyContext>
    {
        public Configuration()
        {
            AutomaticMigrationsEnabled = true;
            AutomaticMigrationDataLossAllowed = true;
        }

        protected override void Seed(MyContext context)
        {
            var a1 = new Account { Name = "a1" };
            var a2 = new Account { Name = "a2" };

            var bill1 = new Bill { Amount = 100, Account = a1 };
            var bill2 = new Bill { Amount = 200, Account = a2 };

            context.Bills.Add(bill1);
            context.Bills.Add(bill2);
            base.Seed(context);
        }
    }

    public static class Test
    {
        public static void Start()
        {
            Database.SetInitializer(new MigrateDatabaseToLatestVersion<MyContext, Configuration>());
            using (var ctx = new MyContext())
            {
                var bill1 = ctx.Bills.Find(1);
                Console.WriteLine(bill1.Amount);
            }
        }
    }
}

using (var ctx = new MyContext())
{
     var bill1 = ctx.Bills.Find(1);
     var a2 = new Account { Id = 2, Name = "a2" };
     bill1.Account = a2;
     ctx.SaveChanges();
}

using (var ctx = new MyContext())
{
    var bill1 = ctx.Bills.Find(1);
    var a2 = ctx.Accounts.Find(2);
    bill1.Account = a2;
    ctx.SaveChanges();
}

public class Bill
{
        public int Id { get; set; }
        public decimal Amount { set; get; }

        [ForeignKey("AccountId")]
        public virtual Account Account { get; set; }
        public int AccountId { set; get; }
}

using (var ctx = new MyContext())
{
    var bill1 = ctx.Bills.Find(1);
    bill1.AccountId = 2;
    ctx.SaveChanges();
}

using (var ctx = new MyContext())
{
     var a2 = new Account { Id = 2, Name = "a2_a2" };
     ctx.Entry(a2).State = System.Data.EntityState.Modified;
     ctx.SaveChanges();
}

    public class Article
    {
        public int Id { get; set; }
        public string Title { get; set; }
        public string Body { get; set; }
        public string RegisterDate { get; set; }
        public string FileName { get; set; }
    }