Control Nodes - Membrane Docs

Control nodes manage the flow of execution, transform data, and implement conditional logic. They help you build complex workflows with branching, filtering, and iteration.

Transform Data

Type: transform-data The Transform Data node transforms input into a new data structure. This is one of the most commonly used nodes, essential for reshaping data between different formats.

transform:
  type: transform-data
  name: Format Contact Data
  config:
    output:
      fullName:
        $eval:
          $concat:
            - $var: input.trigger.fields.firstName
            - ' '
            - $var: input.trigger.fields.lastName
      email:
        $var: input.trigger.fields.email
      createdAt:
        $eval:
          $now: {}
      metadata:
        source: external-app
        syncedAt:
          $eval:
            $now: {}

The output configuration defines the structure of the transformed data. You can use variables ($var), expressions ($eval), or static values. Output: Returns the transformed object as specified in the output configuration:

{
  fullName: 'John Doe',
  email: 'john@example.com',
  createdAt: '2024-01-15T10:30:00Z',
  metadata: {
    source: 'external-app',
    syncedAt: '2024-01-15T10:30:00Z'
  }
}

Filter

Type: filter The Filter node conditionally allows data to continue through the flow. Only inputs that match the filter criteria are passed to downstream nodes.

filter:
  type: filter
  name: Only Active Contacts
  config:
    filter:
      $eval:
        $var: input.findContact.fields.status
      $eq: active

Configuration options:

filter – Filter expression using evaluation syntax (supports $eq, $gt, $and, $or, etc.)

Output: The filter node passes through the input unchanged if it matches the filter. If the input doesn’t match, no output is produced and the flow stops for that input.

For Each

Type: for-each-v2 The For Each node executes a subset of flow nodes for each item in a list, then aggregates their outputs. This is essential for processing arrays of data.

forEach:
  type: for-each-v2
  name: Process Each Contact
  config:
    items:
      $var: input.listContacts
    rootNodeKey: processContact
  links:
    - key: summary

processContact:
  type: transform-data
  name: Transform Contact
  config:
    output:
      id:
        $var: input.forEach.item.id
      fullName:
        $eval:
          $concat:
            - $var: input.forEach.item.fields.firstName
            - ' '
            - $var: input.forEach.item.fields.lastName

summary:
  type: transform-data
  name: Create Summary
  config:
    output:
      processed:
        $var: input.forEach
      normalizedContacts:
        $var: input.forEach.processContact

Configuration options:

items – Array of items to iterate over (usually from a previous node’s output)
rootNodeKey – Key of the first node inside the For Each loop

How it works:

The For Each node receives a list of items
For each item, it executes the nodes inside the loop (starting from rootNodeKey)
Inside the loop, the current item is available as input.forEach.item (where forEach is the key of your for-each node)
All nodes inside the loop run for each item
After all items are processed, outputs are aggregated into a list

Accessing the current item: Inside the For Each loop, access the current item:

$var: input.forEach.item
$var: input.forEach.item.id
$var: input.forEach.item.fields.email

Output structure: The For Each node outputs an object with keys matching the nodes inside the loop, and values being arrays of their outputs:

{
  processContact: [
    { id: '1', fullName: 'John Doe' },
    { id: '2', fullName: 'Jane Smith' }
  ],
  normalizedContacts: [
    { id: '1', fullName: 'John Doe' },
    { id: '2', fullName: 'Jane Smith' }
  ]
}

​Transform Data

​Filter

​For Each

Transform Data

Filter

For Each