elsa-workflows/elsa-core · error · InvalidOperationException

Source label ' ' not found in flowchart

Error message

Source label '{connNode.Source}' not found in flowchart

What it means

CompileFlowchartAsync builds a label-to-activity map for the flowchart's activities, then resolves each connection's endpoints through that map; a connection whose Source label is missing throws InvalidOperationException. Every flowchart connection must reference a label defined by an activity in the same flowchart.

Solutions

1. Fix the connection's source label to exactly match a label of an activity in the flowchart.
2. Ensure each referenced activity is declared inside the flowchart block with the expected label.
3. Remove stale connections after renaming or deleting activities.
4. Catch the exception during compilation and flag the unknown label in the editor.

Example fix

// before
flowchart {
  a: Log("start");
  connect a -> b; // no activity labeled 'b' yet
}
// after
flowchart {
  a: Log("start");
  b: Log("end");
  connect a -> b;
}

const labels = new Set(flowchart.activities.map(a => a.label)); const bad = flowchart.connections.filter(c => !labels.has(c.source)); if (bad.length) throw new Error('Unknown source labels: ' + bad.map(b => b.source).join(', '));

function sourcesResolved(flowchart) { const labels = new Set(flowchart.activities.map(a => a.label)); return flowchart.connections.every(c => labels.has(c.source)); }

try { await compileScript(script); } catch (InvalidOperationException ex) when (ex.Message.StartsWith('Source label')) { highlightUnknownLabel(ex); }

When it happens

Trigger: A FlowchartNode whose Connections list contains a connection with connNode.Source not present in labelToActivity — i.e. the source label does not match any activity's label in the flowchart.

Common situations: Typo in the source label in the connection declaration, an activity removed/renamed while connections still reference the old label, or the activity with that label declared outside this flowchart block.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• Target label ' ' not found in flowchart
• Statement type is not supported
• Activity ' ' not found in registry
• Property ' ' not found on activity type
• Variable ' ' is not declared. Use 'var ' to declare a new…

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/39246dd0acceb722. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Dsl.ElsaScript/Compiler/ElsaScriptCompiler.cs:385

        }

        // Compile all labeled activities and build a label-to-activity map
        var labelToActivity = new Dictionary<string, IActivity>();
        foreach (var labeledNode in flowchart.Activities)
        {
            var activity = await CompileStatementAsync(labeledNode.Activity, cancellationToken);
            if (activity != null)
            {
                labelToActivity[labeledNode.Label] = activity;
            }
        }

        // Create connections
        var connections = new List<Connection>();
        foreach (var connNode in flowchart.Connections)
        {
            if (!labelToActivity.TryGetValue(connNode.Source, out var sourceActivity))
                throw new InvalidOperationException($"Source label '{connNode.Source}' not found in flowchart");

            if (!labelToActivity.TryGetValue(connNode.Target, out var targetActivity))
                throw new InvalidOperationException($"Target label '{connNode.Target}' not found in flowchart");

            var source = new Endpoint(sourceActivity, connNode.Outcome);
            var target = new Endpoint(targetActivity);
            connections.Add(new Connection(source, target));
        }

        // Create flowchart activity
        var flowchartActivity = new Workflows.Activities.Flowchart.Activities.Flowchart
        {
            Activities = labelToActivity.Values.ToList(),
            Connections = connections
        };

        // Set entry point if specified
        if (!string.IsNullOrEmpty(flowchart.EntryPoint))

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