Activity Iterative Activity Node

Iterative Activity Node

An Iterative Activity Node executes a nested Activity repeatedly over partitions of its incoming tokens. AddIterativeActivity<TToken>(..., chunkSize) selects tokens of type TToken, groups them into chunks, and runs the nested graph once per chunk. Other token types are also available inside each nested run.

flowchart LR
    source(Load records) -->|Record tokens| iterate{{Iterative Activity}}
    subgraph body["Nested Activity, once per chunk"]
        input["Input boundary"] --> total(Calculate batch total)
        total --> output["Output boundary"]
    end
    iterate -->|Batch totals| report(Report totals)

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Mermaid approximation: this diagram shows the model's routing, not a complete UML Activity notation. Rounded boxes represent actions; edge labels identify token types or guards. Input/Output boxes name Stateflows boundary APIs, not UML final nodes or a claim that UML uses these box labels. Mermaid does not model pins, activity parameters, or expansion regions natively.

Definition

.AddInitial(initial => initial.AddControlFlow("LoadRecords"))
.AddAction(
    "LoadRecords",
    async c => c.OutputRange(await records.LoadAsync(c.CancellationToken)),
    node => node.AddFlow<Record>("Batch"))
.AddIterativeActivity<Record>("Batch", nested => nested
    .AddInput(input => input.AddFlow<Record>("CalculateBatch"))
    .AddInitial(initial => initial.AddControlFlow("CalculateBatch"))
    .AddAction(
        "CalculateBatch",
        async c =>
        {
            var batchTotal = c.GetTokensOfType<Record>().Sum(record => record.Amount);
            c.Output(batchTotal);
        },
        node => node.AddFlow<decimal, OutputNode>())
    .AddOutput()
    .AddFlow<decimal>("ReportBatch"),
    chunkSize: 25)
.AddAction("ReportBatch", async c =>
    await reports.AddBatchTotalsAsync(
        c.GetTokensOfType<decimal>(), c.CancellationToken))

An OutputNode and AddOutput() are required to collect values from each nested execution. Without an output declaration the nested computation can still perform side effects, but it returns no object tokens to the parent. A FinalNode inside the nested graph ends the iteration early; otherwise all chunks are processed. Iterations run sequentially, unlike the Parallel Activity Node, which runs chunks concurrently. Choose a chunk size appropriate to the amount of data each nested execution should process.

See also Structured Activity Node, Tokens, and Output Node.