Activity Action Node

Action Node

An Action Node performs application work when its incoming flows make it eligible to execute. It is the main executable node in a UML Activity. Incoming object flows provide typed input tokens; the action can produce output tokens and outgoing flows route execution onward.

Define an action

The lambda overload receives an action context and an optional node builder for outgoing flows:

.AddInput(input => input.AddFlow<Request>("Validate"))
.AddAction(
    "Validate",
    async c =>
    {
        var request = c.GetTokensOfType<Request>().Single();
        var validated = await validator.ValidateAsync(request, c.CancellationToken);
        c.Output(validated);
    },
    node => node.AddFlow<ValidatedRequest>("Persist"))
.AddAction(
    "Persist",
    async c => await repository.SaveAsync(
        c.GetTokensOfType<ValidatedRequest>().Single(),
        c.CancellationToken),
    node => node.AddControlFlow<FinalNode>())
.AddFinal()

This fragment receives Request tokens through SendInputAsync. Validate is activated by that input flow; no additional initial control flow is needed for this input-driven path.

Output and OutputRange add object tokens for outgoing flows. GetTokensOfType<T>() reads the input tokens routed to this action. An action can have multiple outgoing control and object flows; use explicit Fork, Decision, or Merge nodes when those routing semantics should be visible in the graph.

Class-based actions

For reusable or dependency-injected logic, define an IActionNode. Constructor parameters can include application services and token interfaces such as IInputTokens<T> and IOutputTokens<T>. The typed class implements ExecuteAsync(CancellationToken); it does not receive a lambda action context parameter.

See Tokens, Flows, and Nodes.