Docs / Strand / templating/nested-workflows

Nested Workflows

Call workflows from other workflows to create modular, reusable designs.

Flow Call Node

The Flow Call node executes another workflow as a step in your current workflow.

Configuration

flow_id (required)

• The ID of the workflow to call
• Can be static: "process-user"
• Can be dynamic using templating: "{{ payload.workflow_to_call }}"

data (optional)

• Custom data to pass to the called workflow
• If not provided, passes current event automatically
• Supports full Jinja2 templating

Example Configuration

Direct connection:

{
  "flow_id": "process-user",
  "data": {
    "user_id": "{{ payload.id }}",
    "context": {
      "source_workflow": "{{ meta.workflow_id }}",
      "timestamp": "{{ meta.received_at }}"
    }
  }
}

Non-direct access:

{
  "flow_id": "process-user",
  "data": {
    "user_id": "{{ steps.user_lookup.output_payload.id }}",
    "context": {
      "source_workflow": "{{ meta.workflow_id }}",
      "timestamp": "{{ meta.received_at }}"
    }
  }
}

Passing Data

Default Behavior

If you don't specify data, the current event is passed:

{
  "payload": { /* current payload */ },
  "meta": { /* current meta */ }
}

Custom Data

Pass a custom object with templating:

Direct connection:

{
  "user_id": "{{ payload.id }}",
  "processed_data": {{ payload | tojson }}
}

Non-direct access:

{
  "user_id": "{{ steps.user_lookup.output_payload.id }}",
  "processed_data": {{ steps.process.output_payload | tojson }}
}

Accessing Output

The nested workflow's output is available through the Flow Call node:

{{ steps.flow_call_node.output_payload }}
{{ steps.flow_call_node.output_payload.result }}

Infinite Loop Prevention

Strand automatically prevents infinite loops by tracking the call chain.

How It Works

1. System tracks which workflows are in the current call chain
2. Before executing a nested workflow, checks if it's already in the chain
3. If detected, raises an error with the full call chain

Error Example

Infinite loop detected: workflow 'workflow-a' is calling itself
(directly or indirectly).
Call chain: workflow-a -> workflow-b -> workflow-a

Best Practices

Use Cases

Modular Processing

Break complex workflows into smaller pieces:

• validate-input - Validates data
• process-data - Processes validated data
• send-notification - Sends notifications

Reusable Components

Create reusable workflow components:

• Authentication workflows
• Data transformation workflows
• Notification workflows

Conditional Execution

Call different workflows based on conditions:

{% if payload.type == 'user' %}
  process-user-workflow
{% else %}
  process-admin-workflow
{% endif %}

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