The execution engine of Hot Chocolate executes resolvers in parallel. This can lead to exceptions because the database context of Entity Framework cannot handle more than one request in parallel. So if you are seeing exceptions like A second operation started on this context before a previous operation completed. or Cannot access a disposed object... the HotChocolate.Data.EnityFramework package has you back. It provides helpers that make EF integration with Hot Chocolate a breeze.

The package was build on the foundation of EntityFramework Core v5.0.0.

Getting Started

You first need to add the package reference to your project. You can do this with the dotnet cli:

dotnet add package HotChocolate.Data.EntityFramework

The execution engine needs more than one database context. You should register the database context in a pool rather than transient. During execution database contexts are taken from this pool and returned once the resolver is completed. This has a smaller memory impact, as creating a new context for each resolver.

services.AddPooledDbContextFactory<SomeDbContext>(b => b /*your configuration */)

⚠️ Note: The configuration of AddPooledDbContextFactory replaces the OnConfiguring method of the DBContext. You have to move the configuration to the factory method if you use OnConfiguring

Using the DBContext

A resolver has to get a database context from the pool, execute the query and then return the context back to the pool. If you annotate a field with UseDbContext() all of this is handled for you

public class Query
{
    [UseDbContext(typeof(SomeDbContext))]
    public IQueryable<User> GetUsers(
        [ScopedService] SomeDbContext someDbContext)
        => someDbContext.Users;
}

⚠️ Note: If you use more than one middleware, keep in mind that ORDER MATTERS. The correct order is UseDbContext > UsePaging > UseProjections > UseFiltering > UseSorting