dotnet/efcore · error · NotImplementedException

Named argument

Error message

Named argument

What it means

VisitInvocationExpression throws NotImplementedException when a method argument uses named-argument syntax (Foo(bar: 1)). The translator currently only handles positional arguments; named arguments are not mapped onto parameters.

Source

Thrown at src/EFCore.Design/Query/Internal/CSharpToLinqTranslator.cs:717

                destArguments[paramIndex] = Constant(
                    parameter.DefaultValue is null && parameter.ParameterType.IsValueType
                        ? Activator.CreateInstance(parameter.ParameterType)
                        : parameter.DefaultValue,
                    parameter.ParameterType);
                continue;
            }

            var argument = invocation.ArgumentList.Arguments[sourceArgIndex++];

            // Positional argument
            if (argument.NameColon is null)
            {
                destArguments[paramIndex] = Visit(argument, parameter.ParameterType);
                continue;
            }

            // Named argument
            throw new NotImplementedException("Named argument");
        }

        Check.DebugAssert(destArguments.All(a => a is not null), "arguments.All(a => a is not null)");

        return Call(instance, methodInfo, destArguments!);

        IEnumerable<KeyValuePair<string, Type>> GetTypeTypeParameters(INamedTypeSymbol typeSymbol)
        {
            // TODO: We match Roslyn type parameters by name, not sure that's right; also for the method's generic type parameters

            if (typeSymbol.ContainingType is { } containingTypeSymbol)
            {
                foreach (var kvp in GetTypeTypeParameters(containingTypeSymbol))
                {
                    yield return kvp;
                }
            }

View on GitHub (pinned to dbf9771522)

Solutions

1. Reorder arguments so they are all positional
2. Remove the name: prefixes from the call

Example fix

// before
var v = ctx.Blogs.Where(b => b.HasFlag(flag: 4));
// after
var v = ctx.Blogs.Where(b => b.HasFlag(4));

// Detect named arguments in precompiled query source.
static bool UsesNamedArg(string src)
    => System.Text.RegularExpressions.Regex.IsMatch(src, @"\b\w+\s*:\s*\w");
if (UsesNamedArg(querySource)) { /* rewrite to positional args */ }

When it happens

Trigger: Any method call inside a precompiled query that uses the name: value syntax, e.g. SomeMethod(x: 1, y: 2).

Common situations: Using named arguments for readability with EF helpers (e.g. Include, HasFlag) or custom utility methods inside a query.

Related errors

• ArrayCreation: non-array type symbol: {implicitArrayCreation
• ArrayCreation: multi-dimensional array: {implicitArrayCreati
• Could not find symbol for method invocation: {invocation}
• Invocation over non-member access: {invocation}
• Invocation: couldn't find method '{methodSymbol.Name}' on ty

AI-assisted analysis of dotnet/efcore@dbf9771522 (2026-08-06). Data as JSON: /api/errors/ec63468a4b5652cd. Report an issue: GitHub.