business-rule-patterns（业务规则模式）

Business Rule Best Practices for ServiceNow

Business Rules are server-side scripts that execute when records are displayed, inserted, updated, or deleted.

When to Use Each Type

Available Objects

// In Business Rules, these are always available:
current // The record being operated on
previous // The record BEFORE changes (update/delete only)
gs // GlideSystem utilities

Before Business Rules

Use for validation and field manipulation:

// Prevent update if condition not met
;(function executeRule(current, previous) {
  if (current.state == 7 && previous.state != 6) {
    current.setAbortAction(true)
    gs.addErrorMessage("Must resolve before closing")
  }
})(current, previous)

// Auto-populate fields
;(function executeRule(current, previous) {
  if (current.isNewRecord()) {
    current.setValue("caller_id", gs.getUserID())
    current.setValue("opened_by", gs.getUserID())
  }
})(current, previous)

Never do in Before rules:

• Call current.update() (causes recursion!)
• Query other tables (keep it fast)
• External API calls

After Business Rules

Use for related record operations:

// Create child record when priority is P1
;(function executeRule(current, previous) {
  if (current.priority.changesTo(1)) {
    var task = new GlideRecord("task")
    task.initialize()
    task.setValue("short_description", "P1 Follow-up: " + current.number)
    task.setValue("parent", current.sys_id)
    task.insert()
  }
})(current, previous)

// Update parent record
;(function executeRule(current, previous) {
  var parent = new GlideRecord("problem")
  if (parent.get(current.problem_id)) {
    parent.setValue("related_incidents", parent.related_incidents + 1)
    parent.update()
  }
})(current, previous)

Async Business Rules

Use for heavy processing that shouldn't block the transaction:

// External integration
;(function executeRule(current, previous) {
  var integrator = new ExternalSystemIntegration()
  integrator.syncIncident(current.sys_id)
})(current, previous)

// Send custom notification
;(function executeRule(current, previous) {
  gs.eventQueue("incident.priority.high", current, current.assigned_to, gs.getUserID())
})(current, previous)

Useful Methods

current Methods

current.isNewRecord() // True if insert
current.isValidRecord() // True if record exists
current.getValue("field") // Get field value
current.setValue("field", val) // Set field value
current.setAbortAction(true) // Cancel the operation
current.operation() // 'insert', 'update', 'delete'
current.isActionAborted() // Check if aborted

Field Change Detection

current.priority.changes() // Field changed (any value)
current.priority.changesTo(1) // Changed TO this value
current.priority.changesFrom(3) // Changed FROM this value
current.priority.nil() // Field is empty

previous Comparisons

// Check if field was modified
if (current.state != previous.state) {
  gs.info("State changed from " + previous.state + " to " + current.state)
}

// Check specific change
if (current.assigned_to.changes() && !previous.assigned_to.nil()) {
  gs.info("Reassignment occurred")
}

Condition Examples

Use conditions to limit when the rule runs:

Performance Best Practices

1. Use conditions - Limit when the rule runs
2. Keep Before rules fast - No queries if possible
3. Use Async for integrations - Don't block transactions
4. Avoid Display rules - Slows form load
5. Set Order - Lower numbers run first (100-500 range)
6. Check "when to run" - insert, update, delete, query

Common Patterns

Auto-Assignment

// Before Insert/Update
if (current.assignment_group.changes() && !current.assignment_group.nil()) {
  var members = new GroupMembers(current.assignment_group)
  current.assigned_to = members.getNextAvailable()
}

Cascade Updates

// After Update
if (current.state.changesTo(7)) {
  // Closed
  var tasks = new GlideRecord("task")
  tasks.addQuery("parent", current.sys_id)
  tasks.addQuery("state", "!=", 7)
  tasks.query()
  while (tasks.next()) {
    tasks.setValue("state", 7)
    tasks.update()
  }
}