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

Podman– Command execution failed with exit code 125

After updating WSL on one of the developer machines, Podman failed to work. When we took a look through Podman Desktop, we noticed that Podman had stopped running and returned the following error message: Error: Command execution failed with exit code 125 Here are the steps we tried to fix the issue: We started by running podman info to get some extra details on what could be wrong: >podman info OS: windows/amd64 provider: wsl version: 5.3.1 Cannot connect to Podman. Please verify your connection to the Linux system using `podman system connection list`, or try `podman machine init` and `podman machine start` to manage a new Linux VM Error: unable to connect to Podman socket: failed to connect: dial tcp 127.0.0.1:2655: connectex: No connection could be made because the target machine actively refused it. That makes sense as the podman VM was not running. Let’s check the VM: >podman machine list NAME         ...
Read more

Cache stampede: when our cache turned against us

While investigating some performance issues, we ran into an ASP.NET Core API that cached a fairly expensive aggregation query for 60 seconds. Under normal load, that was fine: one request rebuilds the cache, everyone else reads from it. Under peak load, dozens of requests would arrive in that same expiry window, all see a cache miss, and all fire the same expensive query in parallel. The database didn't like that. That was the moment when our caching layer stopped helping and started hurting. A burst of requests comes in at the same time, all miss the cache, and all go hammer the database or the downstream API at once. That's a cache stampede . The cache was supposed to protect our backend, and for a few hundred milliseconds it did the opposite. Why this happens IMemoryCache.GetOrCreate (and its async sibling) looks like it protects you, but it doesn't add any locking on its own. Look at the naive version: public async Task<Report> GetReportAsync(string key) ...
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