EntityFrameworkCore Task.WhenAll() A second operation started on this context before a previous operation completed - entity-framework-core

Question

I want to read data from database. For this I create a query and queryhandler classes
QueryHandler
public class OrderGetQueryHandler: IQueryHandler<OrderGetQuery, OrderDTO>
{
private readonly GoodWillWebDbContext _context;
private readonly IQueryDispatcher _queryDispatcher;
public OrderGetQueryHandler(GoodWillWebDbContext context, IQueryDispatcher queryDispatcher)
{
_context = context;
_queryDispatcher = queryDispatcher;
}
private bool CheckPartnerBlock(BlockTypes blockType, decimal debtOverdue, bool payOff)
{
if (blockType == BlockTypes.Block)
return true;
if (blockType == BlockTypes.NotBlock)
return false;
if (blockType == BlockTypes.PreliminaryPayment)
return payOff;
return debtOverdue <= 0;
}
public async Task<OrderDTO> HandleAsync(OrderGetQuery query)
{
var order = await _context.Orders.FindAsync(query.OrderID);
if (order != null)
{
var getCustomerTask = _context.Partners.FindAsync(order.CustomerID).AsTask();
var getCuratorTask = _context.Users.FindAsync(order.CuratorID).AsTask();
var getPaymentTask = _context.Payments.OrderByDescending(x => x.PaymentID).FirstOrDefaultAsync(x => x.CustomerID == order.CustomerID);
var getOrderLinesTask =
_queryDispatcher.HandleAsync<OrderLinesGetQuery, OrderLineDTO[]>(
new OrderLinesGetQuery(query.OrderID));
await Task.WhenAll(getCustomerTask, getCuratorTask, getOrderLinesTask, getPaymentTask);
var priceRange = await _context.PriceRanges.FindAsync(getCustomerTask.Result.PriceRangeID);
return new OrderDTO
(
order.OrderID,
getCustomerTask.Result.Name,
getOrderLinesTask.Result,
order.CustomerID,
order.OrderStateID,
order.CanDelete,
order.CreationDate,
getPaymentTask.Result.DebtBank,
getPaymentTask.Result.DebtOverdue,
this.CheckPartnerBlock(getCustomerTask.Result.BlockTypeID, getPaymentTask.Result.DebtOverdue, order.PayOff),
priceRange.Name,
order.ReservationDate,
Mapper.Convert<DeliveryInfoDTO, BaseEntities.Entities.Sales.Order>(order)
);
}
throw new NullReferenceException();
}
}
this queryhandler i use in ASP.NET WEB Application. My startup class is
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
public void ConfigureServices(IServiceCollection services)
{
services.AddControllers();
string connection = Configuration.GetConnectionString("DefaultConnection");
services.AddDbContext<GoodWillWebDbContext>(options =>
options.UseSqlServer(connection), ServiceLifetime.Transient);
services.AddScoped<IQueryHandler<OrdersGetQuery, BaseEntities.DTO.Sales.Order.OrderDTO[]>, OrdersGetQueryHandler>();
services.AddScoped<IQueryHandler<OrderGetQuery, Sales.Queries.DTO.Order.OrderDTO>, OrderGetQueryHandler>();
services.AddScoped<ICommandDispatcher, CommandDispatcher>();
services.AddScoped<IQueryDispatcher, QueryDispatcher>();
}
// 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();
});
}
}
I set ServiceLifetime.Transient for my context, but I still get an exception: InvalidOperationException A second operation started on this context before a previous operation completed.
What's wrong?

Answer 1

It seems you're running multiple operations on the context without waiting for the previous ones to end, which EF doesn't like:
var getCustomerTask = _context.Partners.FindAsync(order.CustomerID).AsTask();
var getCuratorTask = _context.Users.FindAsync(order.CuratorID).AsTask();
var getPaymentTask = _context.Payments.OrderByDescending(x => x.PaymentID).FirstOrDefaultAsync(x => x.CustomerID == order.CustomerID);
Either make these call sync or use the await keyword.