fix: A second operation was started in DataGrid with EF Core

[davidkudera]

🐛 Bug Report

DataGrid with Paginator in version 3.1.0 and 3.1.1 fails with the following error:

A second operation was started on this context instance before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext.

Sometimes it loads the first time after starting the app but fails on the next request.

💻 Repro or Code Sample

builder.Services.AddFluentUIComponents(options =>
{
    options.HostingModel = BlazorHostingModel.Server;
});

builder.Services.AddDataGridEntityFrameworkAdapter();

<FluentDataGrid Items="@_files" Pagination="_pagination" TGridItem="@File">
    <PropertyColumn Title="Name" Property="@((File f) => f.Name)" Sortable="true" IsDefaultSortColumn="true" InitialSortDirection="SortDirection.Ascending" />
</FluentDataGrid>

<FluentPaginator State="@_pagination" />

@code {

    private readonly PaginationState _pagination = new() { ItemsPerPage = 20 };

    private ApplicationContext? _context;

    private DbSet<File>? _files;

    public void Dispose()
    {
        _context?.Dispose();
    }

    protected override async Task OnInitializedAsync()
    {
        _context = await ContextFactory.CreateDbContextAsync();
        _files = _context.Files;
    }

}

🤔 Expected Behavior

Not to fail.

😯 Current Behavior

info: Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT count(*)::int
      FROM public.file AS f
info: 28.09.2023 11:19:01.627 RelationalEventId.CommandExecuted[20101] (Microsoft.EntityFrameworkCore.Database.Command)
      Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT count(*)::int
      FROM public.file AS f
fail: Microsoft.EntityFrameworkCore.Query[10100]
      An exception occurred while iterating over the results of a query for context type 'ApplicationContext'.
      System.InvalidOperationException: A second operation was started on this context instance 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.
         at Microsoft.EntityFrameworkCore.Infrastructure.Internal.ConcurrencyDetector.EnterCriticalSection()
         at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
      System.InvalidOperationException: A second operation was started on this context instance 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.
         at Microsoft.EntityFrameworkCore.Infrastructure.Internal.ConcurrencyDetector.EnterCriticalSection()
         at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
fail: 28.09.2023 11:19:01.630 CoreEventId.QueryIterationFailed[10100] (Microsoft.EntityFrameworkCore.Query)
      An exception occurred while iterating over the results of a query for context type 'ApplicationContext'.
      System.InvalidOperationException: A second operation was started on this context instance 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.
         at Microsoft.EntityFrameworkCore.Infrastructure.Internal.ConcurrencyDetector.EnterCriticalSection()
         at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
warn: Microsoft.AspNetCore.Components.Server.Circuits.RemoteRenderer[100]
      Unhandled exception rendering component: A second operation was started on this context instance 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.
      System.InvalidOperationException: A second operation was started on this context instance 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.
         at Microsoft.EntityFrameworkCore.Infrastructure.Internal.ConcurrencyDetector.EnterCriticalSection()
         at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
         at System.Linq.Enumerable.TryGetSingle[TSource](IEnumerable`1 source, Boolean& found)
         at lambda_method1928(Closure, QueryContext)
         at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
         at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
         at Microsoft.Fast.Components.FluentUI.FluentDataGrid`1.<BuildRenderTree>b__113_1(RenderTreeBuilder __builder3) in /_/src/Core/Components/DataGrid/FluentDataGrid.razor:line 32
         at Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder.AddContent(Int32 sequence, RenderFragment fragment)
         at Microsoft.Fast.Components.FluentUI.DataGrid.Infrastructure.Defer.BuildRenderTree(RenderTreeBuilder builder) in /_/src/Core/Components/DataGrid/Infrastructure/Defer.cs:line 26
         at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment, Exception& renderFragmentException)
fail: Microsoft.AspNetCore.Components.Server.Circuits.CircuitHost[111]
      Unhandled exception in circuit '1LCf-dBwf8NBgLlwQAp6gSqC2UtUGsOCS6o62lEQi3c'.
      System.InvalidOperationException: A second operation was started on this context instance 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.
         at Microsoft.EntityFrameworkCore.Infrastructure.Internal.ConcurrencyDetector.EnterCriticalSection()
         at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
         at System.Linq.Enumerable.TryGetSingle[TSource](IEnumerable`1 source, Boolean& found)
         at lambda_method1928(Closure, QueryContext)
         at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
         at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
         at Microsoft.Fast.Components.FluentUI.FluentDataGrid`1.<BuildRenderTree>b__113_1(RenderTreeBuilder __builder3) in /_/src/Core/Components/DataGrid/FluentDataGrid.razor:line 32
         at Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder.AddContent(Int32 sequence, RenderFragment fragment)
         at Microsoft.Fast.Components.FluentUI.DataGrid.Infrastructure.Defer.BuildRenderTree(RenderTreeBuilder builder) in /_/src/Core/Components/DataGrid/Infrastructure/Defer.cs:line 26
         at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment, Exception& renderFragmentException)
info: Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT count(*)::int
      FROM public.file AS f
info: 28.09.2023 11:19:01.639 RelationalEventId.CommandExecuted[20101] (Microsoft.EntityFrameworkCore.Database.Command)
      Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT count(*)::int
      FROM public.file AS f
info: Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (2ms) [Parameters=[@__p_1='20', @__p_0='0'], CommandType='Text', CommandTimeout='30']
      SELECT f.id, f.container_name, f.created_at, f.mime, f.name, f.resolution_v2, f.size
      FROM public.file AS f
      ORDER BY f.name
      LIMIT @__p_1 OFFSET @__p_0
info: 28.09.2023 11:19:01.647 RelationalEventId.CommandExecuted[20101] (Microsoft.EntityFrameworkCore.Database.Command)
      Executed DbCommand (2ms) [Parameters=[@__p_1='20', @__p_0='0'], CommandType='Text', CommandTimeout='30']
      SELECT f.id, f.container_name, f.created_at, f.mime, f.name, f.resolution_v2, f.size
      FROM public.file AS f
      ORDER BY f.name
      LIMIT @__p_1 OFFSET @__p_0
info: Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT count(*)::int
      FROM public.file AS f
info: 28.09.2023 11:19:01.674 RelationalEventId.CommandExecuted[20101] (Microsoft.EntityFrameworkCore.Database.Command)
      Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT count(*)::int
      FROM public.file AS f
info: Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT count(*)::int
      FROM public.file AS f
info: 28.09.2023 11:19:01.706 RelationalEventId.CommandExecuted[20101] (Microsoft.EntityFrameworkCore.Database.Command)
      Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT count(*)::int
      FROM public.file AS f

💁 Possible Solution

Downgrade to version 3.0.1

🔦 Context

Print a simple DataGrid with data from DbSet.

🌍 Your Environment

• OS & Device: Windows 11
• Browser: Brave, Chromium 117
• .NET: 7.0.201
• Blazor mode: server
• Microsoft.Fast.Components.FluentUI: 3.1.1
• Microsoft.Fast.Components.FluentUI.DataGrid.EntityFrameworkAdapter: 3.0.0
• EF Core with PostgreSQL: 7.0.10
• Npgsql: 7.0.4

[joecuevasjr]

I'm using v3.1.0 with no issue utilizing pagination. However, I do not set my context in OnInitializedAsync().
Since it's recommended to have a context per operation - Blazor with EF Core - Database Access, consider the following approach:

// Update _context field and remove relevant code from OnInitializedAsync()
private ApplicationContext? _context => ContextFactory.CreateDbContext();

[davidkudera]

@joecuevasjr thanks for your comment, but I'm creating a context per operation (asynchronously): _context = await ContextFactory.CreateDbContextAsync();. I store it in a field so I can dispose it later.

[vnbaaij]

I have very little experience with EF Core. The code for the adapter is almost a one one one copy of what is used with QuickGrid. Would be interesting to see if QuickGrid showed the same behavior

[joecuevasjr]

@davidkudera when the OnInitializedAsync method is called it's only once per component lifetime. It won't rerun for every operation in the component. The call to CreateDbContextAsync() is currently set up as a one time setup when it should be per operation, such as when the data is fetched for the datgrid.

[malcolmvs]

We're having the same issue. Downgrading from v3.1.1 to v3.0.1 appears to resolve this still has the issue intermittently but once I refresh it's workable until it fails again.
We setup our DB context as follows (understood this is scoped by default and is therefore problematic):

services.AddDbContext<OurDbContext>(options => options.UseSqlServer(connectionString));

And then make use of wrapper classes to expose the entities to the page:

IQueryable<Customer> customers = Enumerable.Empty<Customer>().AsQueryable();

    protected override async Task OnInitializedAsync()
    {
        customers = CustomerService.List();
    }

Where List() returns the DB set.

• .NET: 6.0
• Blazor mode: server
• Microsoft.Fast.Components.FluentUI: 3.1.1
• Microsoft.Fast.Components.FluentUI.DataGrid.EntityFrameworkAdapter: 3.0.0
• EF Core with SQL Server: 7.0.10

[joecuevasjr]

The QuickGrid documentation on using EF-Core IQueryable shows the following code example as the simplest and most performant option for EF Core:

@inject ApplicationDbContext MyDbContext

<QuickGrid Items="@MyDbContext.People">
    ...
</QuickGrid>

[malcolmvs]

The QuickGrid documentation on using EF-Core IQueryable shows the following code example as the simplest and most performant option for EF Core:

@inject ApplicationDbContext MyDbContext

<QuickGrid Items="@MyDbContext.People">
    ...
</QuickGrid>

Thanks @joecuevasjr - do you know when MyDbContext will be disposed of in that implementation?

[malcolmvs]

@joecuevasjr correct me if I'm wrong, but calling Items.Count without making use of the asyncQueryExecutor is going to be causing this issue:

fluentui-blazor/src/Core/Components/DataGrid/FluentDataGrid.razor.cs

Line 411 in 2a7634c

int totalItemCount = _asyncQueryExecutor is null ? Items.Count() : await _asyncQueryExecutor.CountAsync(Items);

v3.0.1 does not have the empty check which v3.1.1 does, in which Item.Count is being called - might explain why v3.0.1 works for the most part?

https://github.com/microsoft/fluentui-blazor/blob/v3.0.1/src/Core/Components/DataGrid/FluentDataGrid.razor

fluentui-blazor/src/Core/Components/DataGrid/FluentDataGrid.razor

Line 32 in 2a7634c

@if (Items?.Count() == 0 || _ariaBodyRowCount == 0)

[vnbaaij]

@malcolmvs I don't understand. How can I use the asyncQueryExecutor in line 411 if it is null?

v3.0.1 indeed does not have the empty check because that version did not have the EmptyContent parameter yet. It was added in 3.1.
De we just need to use totalItemCount in the empty check (by turning it in to a privale variable in the class)?

[malcolmvs]

Apologies @vnbaaij I see my comment is unclear. What I was trying to say is that by looking at the code I can see that asyncQueryExecutor needs to be used any time a count of the items is needed (IF the asyncQueryExecutor has been set). Thus the following code will cause an issue as it doesn't take the asyncQueryExecutor into consideration:

fluentui-blazor/src/Core/Components/DataGrid/FluentDataGrid.razor

Line 32 in 2a7634c

@if (Items?.Count() == 0 || _ariaBodyRowCount == 0)

I do believe you could use totalItemCount after exposing it but feel I don't understand the code well enough to be able to comment on a solution.

[vnbaaij]

I think I can fix this by removing the Items?.Count() == 0 part from the line mentioned and just use the _ariaBodyRowCount part.
To make sure the _ariaBodyRowCount is set, I set it immediately after

fluentui-blazor/src/Core/Components/DataGrid/FluentDataGrid.razor.cs

Line 411 in 2a7634c

int totalItemCount = _asyncQueryExecutor is null ? Items.Count() : await _asyncQueryExecutor.CountAsync(Items);

with _ariaBodyRowCount = totalItemCount;.

Sounds good?

[vukasinpetrovic]

@vnbaaij I have the same problem but in my case it is happening if I double click on sorting the column, meaning it executes two operations fast. I'm using basic implementation for testing, without paging or anything additional. Do you have an idea how can I prevent this?

@inject ApplicationDbContext DbContext

<FluentDataGrid Items="@DbContext.Users">
    <PropertyColumn Property="@(u => u.Email)" Sortable="true" Align="Align.Start" />    
    <PropertyColumn Property="@(u => u.UserName)" Sortable="true" Align="Align.Start" />    
</FluentDataGrid>