dotnet/efcore · error · NotSupportedException

Lambda with modifiers not supported: {lambda.Modifiers}

Error message

Lambda with modifiers not supported: {lambda.Modifiers}

What it means

Thrown by VisitLambdaExpression when lambda.Modifiers.Any() is true. The translator rejects any lambda modifier (e.g. the C# 9 'static' modifier on static lambdas) because it only models plain delegates in LINQ expression trees. Part of EF Core's precompiled-query C#-to-LINQ translation.

Source

Thrown at src/EFCore.Design/Query/Internal/CSharpToLinqTranslator.cs:1037

    /// <summary>
    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
    ///     any release. You should only use it directly in your code with extreme caution and knowing that
    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
    /// </summary>
    public override Expression DefaultVisit(SyntaxNode node)
        => throw new NotSupportedException($"Unsupported syntax node of type '{node.GetType()}': {node}");

    private Expression VisitLambdaExpression(AnonymousFunctionExpressionSyntax lambda, Type? expectedType = null)
    {
        if (lambda.ExpressionBody is null)
        {
            throw new NotSupportedException("Lambda with null expression body");
        }

        if (lambda.Modifiers.Any())
        {
            throw new NotSupportedException("Lambda with modifiers not supported: " + lambda.Modifiers);
        }

        if (!lambda.AsyncKeyword.IsKind(SyntaxKind.None))
        {
            throw new NotSupportedException("Async lambdas are not supported");
        }

        var lambdaParameters = lambda switch
        {
            SimpleLambdaExpressionSyntax simpleLambda => SyntaxFactory.SingletonSeparatedList(simpleLambda.Parameter),
            ParenthesizedLambdaExpressionSyntax parenthesizedLambda => parenthesizedLambda.ParameterList.Parameters,

            _ => throw new UnreachableException()
        };

        var translatedParameters = new List<ParameterExpression>();
        foreach (var parameter in lambdaParameters)
        {

View on GitHub (pinned to dbf9771522)

Solutions

Remove the modifier (e.g. drop 'static') from the lambda.
If the lambda must not capture, move it to a static helper method and reference that method directly.

Example fix

// before
.Select(static x => x.Id)
// after
.Select(x => x.Id)

Defensive patterns

Strategy: validation

Validate before calling

foreach (var lambda in root.DescendantNodes().OfType<AnonymousFunctionExpressionSyntax>())
{
    if (lambda.Modifiers.Any())
        throw new InvalidOperationException(
            $"Lambda with modifiers ({string.Join(", ", lambda.Modifiers)}) at {lambda.GetLocation()} is not supported.");
}

Prevention

Avoid static lambdas and other modifiers in query code that will be precompiled.
Document the subset of C# lambda syntax supported by precompiled queries for your team.

When it happens

Trigger: Translating C# source containing a static lambda (static () => ...) or any other lambda modifier during precompiled query processing.

Common situations: Using C# 9+ static anonymous functions/lambdas inside query code that gets precompiled; source generators encountering modern C# lambda modifier syntax.

Related errors

AI-assisted analysis of dotnet/efcore@dbf9771522 (2026-08-06). Data as JSON: /api/errors/a209dc52e6c17f2a. Report an issue: GitHub.