Skip to main content

GraphQL Hot Chocolate - Entity Framework error: 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

 If you try to combine HotChocolate GrapQL implementation together with Entity Framework, a possible attempt could look like this:

Unfortunately this doesn't work the moment multiple resolvers kick in. When you try to resolve multiple queries/fields, chances are you end up with the following exception message:

"message": "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.",

        "stackTrace": "   at Microsoft.EntityFrameworkCore.Internal.ConcurrencyDetector.EnterCriticalSection()\r\n   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.AsyncEnumerator.MoveNextAsync()\r\n   at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.SingleOrDefaultAsync[TSource](IAsyncEnumerable`1 asyncEnumerable, CancellationToken cancellationToken)\r\n   at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.SingleOrDefaultAsync[TSource](IAsyncEnumerable`1 asyncEnumerable, CancellationToken cancellationToken)\r\n   at Bridges.Sectors.Infrastructure.Repositories.SectorRepository.GetSectorById(Guid sectorId) in C:\\Users\\StVa\\source\\repos\\bridges\\Sector\\Bridges.Sectors.Infrastructure\\Repositories\\SectorRepository.cs:line 46\r\n   at Bridges.Sectors.API.Services.SectorService.GetSector(Guid sectorId) in C:\\Users\\StVa\\source\\repos\\bridges\\Sector\\Bridges.Sectors.API\\Services\\SectorService.cs:line 26\r\n   at Bridges.Sectors.API.Schema.Queries.SectorQuery.GetSector(ISectorService sectorService, Guid sectorId) in C:\\Users\\StVa\\source\\repos\\bridges\\Sector\\Bridges.Sectors.API\\Schema\\Queries\\SectorQuery.cs:line 27\r\n   at HotChocolate.Resolvers.Expressions.ExpressionHelper.AwaitTaskHelper[T](Task`1 task)\r\n   at HotChocolate.Types.FieldMiddlewareCompiler.<>c__DisplayClass3_0.<<CreateResolverMiddleware>b__0>d.MoveNext()\r\n--- End of stack trace from previous location ---\r\n   at HotChocolate.Execution.Processing.ResolverTask.ExecuteResolverPipelineAsync(CancellationToken cancellationToken)\r\n   at HotChocolate.Execution.Processing.ResolverTask.TryExecuteAsync(CancellationToken cancellationToken)",

This is because HotChocolate executes multiple resolvers in parallel and the DbContext is inherently not threadsafe. More about this here.

You could try to go for a single threaded execution model but this would end up being a fight against GraphQL.

Luckily the creators of HotChocolate got your back and created a HotChocolate.Data.EntityFramework nuget package. This package allows you to create a pool of DbContexts and use these in your resolvers.

First register a DbContext pool:

And then we can update our code to use a DbContext instance from this pool:

More information about this feature here:https://chillicream.com/docs/hotchocolate/integrations/entity-framework 

Labels:

Popular posts from this blog

DevToys–A swiss army knife for developers

As a developer there are a lot of small tasks you need to do as part of your coding, debugging and testing activities.  DevToys is an offline windows app that tries to help you with these tasks. Instead of using different websites you get a fully offline experience offering help for a large list of tasks. Many tools are available. Here is the current list: Converters JSON <> YAML Timestamp Number Base Cron Parser Encoders / Decoders HTML URL Base64 Text & Image GZip JWT Decoder Formatters JSON SQL XML Generators Hash (MD5, SHA1, SHA256, SHA512) UUID 1 and 4 Lorem Ipsum Checksum Text Escape / Unescape Inspector & Case Converter Regex Tester Text Comparer XML Validator Markdown Preview Graphic Color B
Read more

Help! I accidently enabled HSTS–on localhost

I ran into an issue after accidently enabling HSTS for a website on localhost. This was not an issue for the original website that was running in IIS and had a certificate configured. But when I tried to run an Angular app a little bit later on http://localhost:4200 the browser redirected me immediately to https://localhost . Whoops! That was not what I wanted in this case. To fix it, you need to go the network settings of your browser, there are available at: chrome://net-internals/#hsts edge://net-internals/#hsts brave://net-internals/#hsts Enter ‘localhost’ in the domain textbox under the Delete domain security policies section and hit Delete . That should do the trick…
Read more

Azure DevOps/ GitHub emoji

I’m really bad at remembering emoji’s. So here is cheat sheet with all emoji’s that can be used in tools that support the github emoji markdown markup: All credits go to rcaviers who created this list.
Read more