flow-designer（流程设计师）

Flow Designer Patterns for ServiceNow

Flow Designer is the modern automation engine in ServiceNow, replacing legacy Workflows for new development.

Using the Flow Designer Tool

To create and manage flows programmatically, first discover the Flow Designer tool via tool_search({query: "flow designer"}). The discovered tool handles all GraphQL mutations for the full flow lifecycle.

CRITICAL — IF/ELSE/ELSEIF placement rules:

• Actions inside an IF branch: parent_ui_id = IF's uiUniqueIdentifier
• ELSE/ELSEIF blocks: must be at the same level as IF, NOT nested inside it

- parent_ui_id = the same parent you used for the IF block - connected_to = IF's logicId (the sysId returned when creating the IF)

• Getting this wrong causes "Unsupported flowLogic type" errors when saving the flow

Flow Designer Components

Flow Triggers

Record-Based Triggers

Trigger: Created
Table: incident
Condition: Priority = 1

Trigger: Updated
Table: incident
Condition: State changes to Resolved

Trigger: Created or Updated
Table: change_request
Condition: Risk = High

Schedule Triggers

Trigger: Daily
Time: 02:00 AM
Timezone: America/New_York

Trigger: Weekly
Day: Monday
Time: 08:00 AM

Service Catalog Triggers

Trigger: Service Catalog
Catalog Item: Request New Laptop

Flow Best Practices

1. Use Subflows for Reusability

Main Flow: Incident P1 Handler
├── Trigger: Incident Created (Priority = 1)
├── Action: Log Event
├── Subflow: Notify On-Call Team     ← Reusable!
├── Subflow: Create Major Incident   ← Reusable!
└── Action: Update Incident

2. Error Handling

Flow: Process Integration
├── Try
│   ├── Action: Call REST API
│   ├── Action: Parse Response
│   └── Action: Update Record
├── Catch (all errors)
│   ├── Action: Log Error Details
│   ├── Action: Create Error Task
│   └── Action: Send Alert
└── Always
    └── Action: Cleanup Temp Data

3. Flow Variables

// Input Variables (from trigger)
var incidentSysId = fd_data.trigger.current.sys_id
var priority = fd_data.trigger.current.priority

// Scratch Variables (within flow)
fd_data.scratch.approval_required = priority == "1"
fd_data.scratch.notification_sent = false

// Output Variables (to calling flow/subflow)
fd_data.output.success = true
fd_data.output.message = "Processed successfully"

4. Conditions and Branches

If: Priority = Critical
  Then:
    - Notify VP
    - Create Major Incident
    - Page On-Call
  Else If: Priority = High
    - Notify Manager
    - Escalate in 4 hours
  Else:
    - Standard Processing

Custom Actions (Scripts)

Basic Script Action

;(function execute(inputs, outputs) {
  // Inputs defined in Action Designer
  var incidentId = inputs.incident_sys_id
  var newState = inputs.target_state

  // Process
  var gr = new GlideRecord("incident")
  if (gr.get(incidentId)) {
    gr.setValue("state", newState)
    gr.update()

    // Set outputs
    outputs.success = true
    outputs.incident_number = gr.getValue("number")
  } else {
    outputs.success = false
    outputs.error_message = "Incident not found"
  }
})(inputs, outputs)

Script Action with Error Handling

;(function execute(inputs, outputs) {
  try {
    var gr = new GlideRecord(inputs.table_name)
    gr.addEncodedQuery(inputs.query)
    gr.query()

    var records = []
    while (gr.next()) {
      records.push({
        sys_id: gr.getUniqueValue(),
        display_value: gr.getDisplayValue(),
      })
    }

    outputs.records = JSON.stringify(records)
    outputs.count = records.length
    outputs.success = true
  } catch (e) {
    outputs.success = false
    outputs.error_message = e.message
    // Flow Designer will catch this and route to error handler
    throw new Error("Query failed: " + e.message)
  }
})(inputs, outputs)

REST Action Example

Configuration

Action: Call External API
Connection: My REST Connection Alias
HTTP Method: POST
Endpoint: /api/v1/tickets

Headers:
  Content-Type: application/json
  Authorization: Bearer ${connection.credential.token}

Request Body:
{
  "title": "${inputs.short_description}",
  "priority": "${inputs.priority}",
  "reporter": "${inputs.caller_email}"
}

Parse Response: JSON

Response Handling

// In a Script step after REST call
var response = fd_data.action_outputs.rest_response

if (response.status_code == 201) {
  outputs.external_id = response.body.id
  outputs.success = true
} else {
  outputs.success = false
  outputs.error = response.body.error || "Unknown error"
}

Subflow Patterns

Notification Subflow

Subflow: Send Notification
Inputs:
  - recipient_email (String)
  - subject (String)
  - body (String)
  - priority (String, default: "normal")

Actions:
  1. Look Up: User by email
  2. If: User found
     - Send Email notification
     - Output: success = true
  3. Else:
     - Log Warning
     - Output: success = false

Approval Subflow

Subflow: Request Approval
Inputs:
  - record_sys_id (Reference)
  - approver (Reference: sys_user)
  - approval_message (String)

Actions:
  1. Create: Approval record
  2. Wait: For approval state change
  3. If: Approved
     - Output: approved = true
  4. Else:
     - Output: approved = false
     - Output: rejection_reason = comments

Flow Designer vs Workflow

Debugging Flows

Flow Context Logs

// In Script Action
fd_log.info("Processing incident: " + inputs.incident_number)
fd_log.debug("Input data: " + JSON.stringify(inputs))
fd_log.warn("Retry attempt: " + inputs.retry_count)
fd_log.error("Failed to process: " + error.message)

Flow Execution History

Navigate: Flow Designer > Executions
Filter by: Flow name, Status, Date range
View: Step-by-step execution details

Common Patterns

Pattern 1: SLA Escalation Flow

Trigger: SLA breached (Task SLA)
Actions:
  1. Get: Task details
  2. Get: Assignment group manager
  3. Send: Escalation email
  4. Update: Task priority
  5. Create: Escalation task

Pattern 2: Approval Routing

Trigger: Request Item created
Actions:
  1. If: Amount < $1000
     - Auto-approve
  2. Else If: Amount < $10000
     - Request: Manager approval
  3. Else:
     - Request: VP approval
     - Wait: 3 business days
     - If timeout: Escalate to CFO

Pattern 3: Integration Sync

Trigger: Scheduled (every 15 minutes)
Actions:
  1. Call: External API (get changes)
  2. For Each: Changed record
     a. Look Up: Matching local record
     b. If exists: Update
     c. Else: Create
  3. Log: Sync summary

Performance Tips

1. Use conditions early - Filter before expensive operations
2. Limit loops - Set max iterations on For Each
3. Async where possible - Don't block on slow operations
4. Cache lookups - Store repeated queries in scratch variables
5. Batch operations - Group similar updates together