services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(connectionString));
public static IServiceCollection AddDbContext<TContext>(
[NotNullAttribute] this IServiceCollection serviceCollection,
[CanBeNullAttribute] Action<DbContextOptionsBuilder> optionsAction = null,
ServiceLifetime contextLifetime = ServiceLifetime.Scoped,
ServiceLifetime optionsLifetime = ServiceLifetime.Scoped) where TContext : DbContext; An exception occurred while iterating over the results of a query for context type 'BlazorServer.DataAccess.ApplicationDbContext'. System.InvalidOperationException: A second operation was started on this context before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext. For more information on how to avoid threading issues with DbContext, see https://go.microsoft.com/fwlink/?linkid=2097913.
public void ConfigureServices(IServiceCollection services)
{
var connectionString = Configuration.GetConnectionString("DefaultConnection");
//services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(connectionString));
services.AddDbContextFactory<ApplicationDbContext>(options => options.UseSqlServer(connectionString)); @inject IDbContextFactory<ApplicationDbContext> DbFactory
private async Task DeleteImageAsync()
{
using var context = DbFactory.CreateDbContext();
var image = await context.HotelRoomImages.FindAsync(1);
// ...
} @implements IDisposable
@inject IDbContextFactory<ApplicationDbContext> DbFactory
@code
{
private ApplicationDbContext Context;
protected override async Task OnInitializedAsync()
{
Context = DbFactory.CreateDbContext();
await base.OnInitializedAsync();
}
private async Task DeleteImageAsync()
{
var image = await Context.HotelRoomImages.FindAsync(1);
// ...
}
public void Dispose()
{
Context.Dispose();
}
} services.AddScoped<ApplicationDbContext>(serviceProvider =>
serviceProvider.GetRequiredService<IDbContextFactory<ApplicationDbContext>>().CreateDbContext()); public interface IHotelRoomService : IDisposable
{
// ...
}
public interface IHotelRoomImageService : IDisposable
{
// ...
} public class HotelRoomService : IHotelRoomService
{
private bool _isDisposed;
// ...
public void Dispose()
{
Dispose(disposing: true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!_isDisposed)
{
try
{
if (disposing)
{
_dbContext.Dispose();
}
}
finally
{
_isDisposed = true;
}
}
}
} @page "/hotel-room/create"
@page "/hotel-room/edit/{Id:int}"
@implements IDisposable
// ...
@code
{
// ...
public void Dispose()
{
HotelRoomImageService.Dispose();
HotelRoomService.Dispose();
}
} @page "/hotel-room"
@implements IDisposable
// ...
@code
{
// ...
public void Dispose()
{
HotelRoomService.Dispose();
}
} System.ObjectDisposedException: Cannot access a disposed context instance. A common cause of this error is disposing a context instance that was resolved from dependency injection and then later trying to use the same context instance elsewhere in your application. This may occur if you are calling 'Dispose' on the context instance, or wrapping it in a using statement. If you are using dependency injection, you should let the dependency injection container take care of disposing context instances. Object name: 'ApplicationDbContext'.
@code
{
private IHotelRoomImageService HotelRoomImageService;
protected override async Task OnInitializedAsync()
{
HotelRoomImageService = new HotelRoomImageService(DbFactory.CreateDbContext(), mapper);
await base.OnInitializedAsync();
}
private async Task DeleteImageAsync()
{
await HotelRoomImageService.DeleteAsync(1);
// ...
}
public void Dispose()
{
HotelRoomImageService.Dispose();
}
} @page "/hotel-room" @*@implements IDisposable*@ @*@inject IHotelRoomService HotelRoomService*@ @inherits OwningComponentBase<IHotelRoomService>
@code
{
private IHotelRoomService HotelRoomService => Service; @page "/preferences"
@using Microsoft.Extensions.DependencyInjection
@inherits OwningComponentBase
@code {
private IHotelRoomService HotelRoomService { get; set; }
private IHotelRoomImageService HotelRoomImageService { get; set; }
protected override void OnInitialized()
{
HotelRoomService = ScopedServices.GetRequiredService<IHotelRoomService>();
HotelRoomImageService = ScopedServices.GetRequiredService<IHotelRoomImageService>();
}
} services.AddDbContextFactory<ApplicationDbContext>(options => options.UseSqlServer(connectionString));
services.AddScoped<ApplicationDbContext>(serviceProvider =>
serviceProvider.GetRequiredService<IDbContextFactory<ApplicationDbContext>>().CreateDbContext()); @inject IHotelRoomService HotelRoomService
@inherits OwningComponentBase<IHotelRoomService>
create table t1
(
col1 char(1),
col2 char(1)
)
create unique nonclustered index ix_uq on t1 (col1 , col2);
insert t1
values('A', 'B'), ('B', 'C'), ('C', 'D'), ('D', 'E'), ('E', 'F'),
('G', 'H'), ('I', 'J'), ('K', 'L'), ('M', 'N'), ('O', 'P');
select col1 + col2 from t1 where col1 + col2 = 'OP'
select col1 + col2 from t1 where col1 = 'O' and col2 = 'P'
alter table t1 add col3 as col1 + col2 persisted create clustered index ix1 on t1 (col3)
select * from t1 where col3 = 'OP';
سپس وارد مرحله Preview Data Source Result می‌شوید که در آن قادر خواهید بود پیش نمایشی از داده هایی که بعدا توسط Query ساخته شده بارگذاری خواهند شد را مشاهده نمایید. Next را کلیک نموده تا وارد مرحله بعد شوید.مرحله بعد Standard Report Type می‌باشد که در این مرحله شما می‌توانید نوع گزارش خود را انتخاب نمایید و کلید Next را فشار دهید.در بخش Design Data Layout چند فیلد را از بخش سمت چپ (Available Fields) انتخاب نموده و کلید Details را کلیک نمایید.فیلدهای انتخاب شده به بخش Details گزارش اضافه خواهند شد.در ادامه Next را کلیک کنید تا وارد بخش Choose Report Layout شوید.شما می‌توانید در این بخش یک حالت نمایشی را برای گزارش خود انتخاب نمایید و Next را کلیک نمایید.در بخش Choose Report Style یک قالب بندی جهت گزارش خود انتخاب نمایید.در ادامه Next و سپس Finish را کلیک نمایید.کدهای گزارش Generate شده می‌توان در قسمت Designer گزارش را مشاهده نمود.
در این حالت کارهای زیر توسط Wizard به صورت اتوماتیک انجام خواهد شد:
• بایند شدن اتوماتیک فیلدهای گزارش به ستوان‌های مرتبط
• اعمال قالب بندی انتخاب شده برای صفحه و سر ستونها
• افزودن تاریخ و شماره صفحه به پایین گزارش
در ادامه پروژه را Rebuild کرده و گزینه Preview را در Designer جهت نمایش ، پیش نمایش گزارش کلیک نمایید.
urlSearchParams.append('grant_type', 'refresh_token');
urlSearchParams.append('refresh_token', model.refreshToken); 
public abstract class Entity
{
public Guid Id { get; set; }
} public class Book : EntityBase
{
public string Name { get; set; }
public decimal Author { get; set; }
} public class BookRepository
{
private readonly ConcurrentDictionary<Guid, Book> result = new ConcurrentDictionary<Guid, Book>();
public IQueryable<Book> GetAll()
{
return result.Values.AsQueryable();
}
public Book Add(Book entity)
{
if (entity.Id == Guid.Empty) entity.Id = Guid.NewGuid();
if (result.ContainsKey(entity.Id)) return null;
if (!result.TryAdd(entity.Id, entity)) return null;
return entity;
}
} public class BooksController : ApiController
{
public static BookRepository repository = new BookRepository();
public BooksController()
{
repository.Add(new Book
{
Id=Guid.NewGuid(),
Name="C#",
Author="Masoud Pakdel"
});
repository.Add(new Book
{
Id = Guid.NewGuid(),
Name = "F#",
Author = "Masoud Pakdel"
});
repository.Add(new Book
{
Id = Guid.NewGuid(),
Name = "TypeScript",
Author = "Masoud Pakdel"
});
}
public IEnumerable<Book> Get()
{
return repository.GetAll().ToArray();
}
} module Model {
export class Book{
Id: string;
Name: string;
Author: string;
}
} <div ng-controller="Books.Controller">
<table class="table table-striped table-hover" style="width: 500px;">
<thead>
<tr>
<th>Name</th>
<th>Author</th>
</tr>
</thead>
<tbody>
<tr ng-repeat="book in books">
<td>{{book.Name}}</td>
<td>{{book.Author}}</td>
</tr>
</tbody>
</table>
</div> declare module AngularModule {
export interface HttpPromise {
success(callback: Function) : HttpPromise;
}
export interface Http {
get(url: string): HttpPromise;
}
} /// <reference path='AngularModule.ts' />
/// <reference path='BookModel.ts' />
module Books {
export interface Scope {
books: Model.Book[];
}
export class Controller {
private httpService: any;
constructor($scope: Scope, $http: any) {
this.httpService = $http;
this.getAllBooks(function (data) {
$scope.books = data;
});
var controller = this;
}
getAllBooks(successCallback: Function): void {
this.httpService.get('/api/books').success(function (data, status) {
successCallback(data);
});
}
}
} /// <reference path='AngularModule.ts' /> /// <reference path='BookModel.ts' />
export interface Scope {
books: Model.Book[];
} 
public class Person
{
public string FullName {
get
{
return FirstName + " " + LastName;
}
}
} public partial class Person
{
public string FirstName {get; set;}
public string LastName {get; set; }
}
public partial class Person
{
public string FullName {
get
{
return FirstName + " " + LastName;
}
}
} 
protected void Application_Start() {
//...
Database.SetInitializer(...همانند سابق...);
using (var context = new MyContext()) {
context.Database.Initialize(force: true);
}
//...
}