dotnet/efcore · error · OperationException

The exception '{rootException}' was thrown while attempting

Error message

The exception '{rootException}' was thrown while attempting to find 'DbContext' types. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

What it means

Thrown as OperationException by DbContextOperations.FindContextTypes when an unexpected (non-OperationException, non-TargetInvocationException after unwrap) exception occurs while discovering DbContext types. The original exception is wrapped with its message. This covers failures in the discovery pipeline itself: scanning assemblies, reading attributes, building the service provider, or invoking design-time factories.

Source

Thrown at src/EFCore.Design/Design/Internal/DbContextOperations.cs:693

                {
                    var context = contextPair.Key;
                    contexts[context] = CreateContextFromServiceProvider(appServices, context);
                }
            }
        }
        catch (Exception ex)
        {
            if (ex is OperationException)
            {
                throw;
            }

            if (ex is TargetInvocationException)
            {
                ex = ex.InnerException!;
            }

            throw new OperationException(DesignStrings.CannotFindDbContextTypes(ex.Message), ex);
        }

        return contexts!;
    }

    private static Func<DbContext> CreateContextFromServiceProvider(IServiceProvider appServices, Type contextType)
    {
        var factoryInterface = typeof(IDbContextFactory<>).MakeGenericType(contextType);
        var factoryService = appServices.GetService(factoryInterface);
        return factoryService == null
            ? () => (DbContext)ActivatorUtilities.GetServiceOrCreateInstance(appServices, contextType)
            : () => (DbContext)factoryInterface
                .GetMethod(nameof(IDbContextFactory<DbContext>.CreateDbContext))
                !.Invoke(factoryService, null)!;
    }

    private Func<DbContext>? FindContextFactory(Type contextType)
    {

View on GitHub (pinned to dbf9771522)

Solutions

Read the wrapped exception message to identify the root failure during discovery and resolve it (missing assembly, bad config, etc.).
Ensure --startup-project builds and runs cleanly; many discovery failures stem from a broken host build.
Add or fix an IDesignTimeDbContextFactory<TContext> so discovery does not depend on full host construction.
Restore all packages and verify referenced assemblies are present (resolve ReflectionTypeLoadException).

Example fix

// before - host throws during discovery because of a missing config/dependency
dotnet ef migrations list  // CannotFindDbContextTypes wrapping the host error

// after - add a design-time factory that bypasses host construction
public class AppDbContextFactory : IDesignTimeDbContextFactory<AppDbContext>
{
    public AppDbContext CreateDbContext(string[] args)
    {
        var opts = new DbContextOptionsBuilder<AppDbContext>()
            .UseSqlServer("Server=.;Database=App;Trusted_Connection=True");
        return new AppDbContext(opts.Options);
    }
}

Defensive patterns

Strategy: try-catch

Try / catch

try { var types = ops.GetContextTypes(); }
catch (OperationException ex) when (ex.Message.Contains("was thrown while attempting to find 'DbContext' types"))
{
    // inspect ex.InnerException for the root failure during discovery and resolve it
}

Prevention

Ensure the startup project builds and runs without throwing during host construction.
Add an IDesignTimeDbContextFactory to bypass full host build during discovery.
Restore all packages so referenced assemblies load cleanly.
Resolve ReflectionTypeLoadException by providing missing referenced assemblies.

When it happens

Trigger: Any EF tooling operation that triggers context discovery when the discovery process throws. Examples: the startup assembly cannot be loaded, GetConstructibleTypes fails, the AppServiceProviderFactory.Create throws while building the host, or an IDesignTimeDbContextFactory.CreateDbContext throws during scanning.

Common situations: The startup project throws during service-provider construction (Program.Main / ConfigureServices). An assembly load failure (missing dependency, version mismatch). A design-time factory or hosting setup that fails at design time. Type-scanning hits a ReflectionTypeLoadException from a referenced assembly that is not present.

Related errors

AI-assisted analysis of dotnet/efcore@dbf9771522 (2026-08-06). Data as JSON: /api/errors/b477826455f406eb. Report an issue: GitHub.