elsa-workflows/elsa-core · error · InvalidOperationException

Property ' ' not found on activity type

Error message

Property '{arg.Name}' not found on activity type '{activityType.Name}'

What it means

While compiling an activity invocation, named arguments are mapped onto CLR properties of the activity type via reflection; if a named argument has no matching property on the activity type, the compiler throws InvalidOperationException naming the argument and activity type. The script passed a property the activity does not declare.

Solutions

1. Fix the argument name to match the activity's property (Elsa inputs are C# properties, matching by exact name).
2. Check the activity's input definitions/descriptor for the correct property names.
3. Upgrade the activity package if the script targets an older property name; or update the script after a rename.
4. Catch InvalidOperationException during compilation and highlight the offending argument in the editor.

Example fix

// before
httpGet(url: "https://example.com")   // property is 'Url'
// after
httpGet(Url: "https://example.com")

const descriptor = await registry.find(d => d.name === invocation.name); const bad = invocation.args.filter(a => a.name && !descriptor.inputs?.some(p => p.name === a.name)); if (bad.length) throw new Error('Unknown properties: ' + bad.map(b => b.name).join(', '));

function argsMatchDescriptor(args, descriptor) { return args.every(a => !a.name || descriptor.inputs.some(p => p.name === a.name)); }

try { await compileScript(script); } catch (InvalidOperationException ex) when (ex.Message.Contains("not found on activity type")) { highlightBadArgument(ex); }

When it happens

Trigger: Invoking an activity with a named argument (arg.Name) that does not correspond to any public settable property on the resolved activityDescriptor.ClrType.

Common situations: Typo in a named argument (e.g. 'url' vs 'Url'), argument names from an older activity version that was renamed, or passing non-input fields that are not exposed as properties.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Value cannot be null. (Parameter 'type')
• Multiple Invoke methods were found. Use either Invoke or…
• No Invoke methods were found. Use either Invoke or…
• The method must return Task or ValueTask
• Type not found.

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/64098444faea1dc3. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Dsl.ElsaScript/Compiler/ElsaScriptCompiler.cs:223

            // No positional arguments, use default constructor
            var activityConstructorContext = new ActivityConstructorContext(activityDescriptor, (t) => new(ActivityActivator.Create(t)));
            var activityConstructionResult = activityDescriptor.Constructor(activityConstructorContext);
            activity = activityConstructionResult.Activity;
        }

        // Set named argument properties
        foreach (var arg in namedArgs)
        {
            var property = activityType.GetProperty(arg.Name!);

            if (property != null)
            {
                var value = CompileExpression(arg.Value, property.PropertyType);
                property.SetValue(activity, value);
            }
            else
            {
                throw new InvalidOperationException($"Property '{arg.Name}' not found on activity type '{activityType.Name}'");
            }
        }

        return activity;
    }

    private async Task<IActivity> CompileBlockAsync(BlockNode block, CancellationToken cancellationToken = default)
    {
        var activities = new List<IActivity>();

        foreach (var statement in block.Statements)
        {
            var activity = await CompileStatementAsync(statement, cancellationToken);
            if (activity != null)
            {
                activities.Add(activity);
            }
        }

View on GitHub (pinned to fe9217bdfa)