microsoft/aspire · error · NotSupportedException

Unsupported value type

Error message

Unsupported value type {value.GetType()}

What it means

ProcessValue converts environment-variable/argument values for the website into Bicep parameters or secret references. It understands strings, primitives, IManifestExpressionProvider, and secret reference types; when it receives a value type outside its handled set it throws this NotSupportedException reporting the concrete CLR type via value.GetType().

Solutions

1. Convert the value to a supported type before it reaches ProcessValue: use a string, a primitive, or an IManifestExpressionProvider (e.g. ReferenceExpression).
2. If passing connection/endpoint objects, pass their .Value / expression form rather than the wrapper object.
3. If you own a custom value provider, implement IManifestExpressionProvider so it resolves to a manifest expression.
4. Inspect the reported type in the message to identify exactly which value failed and add a case for it if you're modifying the library.

Example fix

// before
api.WithEnvironment("MY_VALUE", new MyCustomValue());
// after
api.WithEnvironment("MY_VALUE", ReferenceExpression.Create($"{myCustomValue}")); // or .ToString()/string value

static bool IsSupportedProcessValueType(object v) =>
    v is string or IManifestExpressionProvider or IAzureKeyVaultSecretReference || v is int or long or bool;

if (value is not (string or IManifestExpressionProvider))
    throw new ArgumentException($"Convert {value.GetType().Name} to a string, ReferenceExpression, or secret reference before App Service processing.");

try { var (param, _) = ctx.ProcessValue(value, secretType); }
catch (NotSupportedException ex) when (ex.Message.StartsWith("Unsupported value type"))
{
    value = value.ToString(); // or wrap in ReferenceExpression
    var (param, _) = ctx.ProcessValue(value, secretType);
}

When it happens

Trigger: Calling ProcessValue (directly or through environment/argument processing) with an unhandled object type — e.g. a custom IValueProvider that is not an IManifestExpressionProvider, a complex object, a BicepValue, or a raw Guid/DateTime not converted to string.

Common situations: Custom annotations supplying bespoke value types to WithEnvironment/args; passing connection-string or endpoint objects instead of their string/manifest forms; version changes where new value types (e.g. BicepValue inputs) were introduced but ProcessValue wasn't extended.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• Unsupported value type
• Command line args must be strings
• Infra is not set
• The property ' ' is not supported for the endpoint ' '.
• Unsupported endpoint property

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/305a5f7cf06d4afd. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting.Azure.AppService/AzureAppServiceWebsiteContext.cs:309

                }

                if (expr.StringFormats[index] is string format)
                {
                    val = BicepFormattingHelpers.FormatBicepExpression(val, format);
                }

                args[index++] = val;
            }

            return (FormattableStringFactory.Create(expr.Format, args), finalSecretType);
        }

        if (value is IManifestExpressionProvider manifestExpressionProvider)
        {
            return (AllocateParameter(manifestExpressionProvider, secretType), secretType);
        }

        throw new NotSupportedException($"Unsupported value type {value.GetType()}");
    }

    private static BicepValue<string> ResolveValue(object val)
    {
        return val switch
        {
            BicepValue<string> s => s,
            string s => s,
            ProvisioningParameter p => p,
            FormattableString fs => BicepFunction.Interpolate(fs),
            _ => throw new NotSupportedException($"Unsupported value type {val.GetType()}")
        };
    }

    public void BuildWebSite(AzureResourceInfrastructure infra)
    {
        _infrastructure = infra;

View on GitHub (pinned to 25830f84bd)