Blocks ReferenceFunction
filter
Filter messages based on specified criteria to enable selective processing of data streams.
filter Block
The filter block is a Report by Exception (RBE) node - only passes on data if the payload has changed. It can also block unless, or ignore if the value changes by a specified amount (Dead- and Narrowband mode).
Overview
The filter block evaluates incoming messages against defined rules and decides whether to pass them through or block them. It supports various filtering modes:
- Property Filtering: Filter based on message properties
- Value Filtering: Filter based on specific values
- Expression Filtering: Filter using JavaScript expressions
- Type Filtering: Filter based on data types
- Conditional Filtering: Filter based on complex conditions
Configuration Options
Filter Mode
Choose the type of filtering to apply:
Simple Property Filter
- Property: The message property to check
- Operator: Comparison operator (equals, not equals, contains, etc.)
- Value: The value to compare against
Expression Filter
- Expression: JavaScript expression to evaluate
- Expected Result: What the expression should return to pass the filter
Type Filter
- Property: The message property to check
- Type: Expected data type (string, number, boolean, object, array)
Filter Behavior
- Pass Through: What happens when the filter condition is met
- Block: What happens when the filter condition is not met
- Multiple Rules: How to handle multiple filter rules
Common Filter Types
Property Exists Filter
Check if a property exists in the message:
// Configuration
Property: msg.payload.userId;
Operator: exists;
// Result: Passes if userId exists, blocks if it doesn'tValue Comparison Filter
Compare property values:
// Configuration
Property: msg.payload.status;
Operator: equals;
Value: "active";
// Result: Passes if status equals "active"Range Filter
Filter numeric values within a range:
// Configuration
Property: msg.payload.score;
Operator: between;
Value: 80, 100;
// Result: Passes if score is between 80 and 100Array Contains Filter
Check if an array contains a value:
// Configuration
Property: msg.payload.tags;
Operator: contains;
Value: "urgent";
// Result: Passes if tags array contains "urgent"Expression Filter
Use complex JavaScript expressions:
// Configuration
Expression: msg.payload.priority === "high" && msg.payload.assigned !== null
Expected Result: true
// Result: Passes if both conditions are trueUse Cases
Data Validation
Filter out invalid or incomplete data:
input → filter (valid data) → processing → output
↓
filter (invalid data) → error handlingPriority Processing
Route high-priority messages differently:
input → filter (high priority) → fast processing
↓
filter (normal priority) → standard processingContent Filtering
Filter messages based on content:
input → filter (contains keywords) → analysis
↓
filter (no keywords) → standard processingRate Limiting
Filter messages to implement rate limiting:
input → filter (rate limit) → processing
↓
filter (rate exceeded) → queue or dropCommon Patterns
Multi-Stage Filtering
// Stage 1: Filter by type
Property: msg.payload.type
Operator: equals
Value: "document"
// Stage 2: Filter by status
Property: msg.payload.status
Operator: equals
Value: "ready"
// Stage 3: Filter by size
Property: msg.payload.size
Operator: less than
Value: 10485760 // 10MBConditional Processing
// High priority path
Property: msg.payload.priority
Operator: equals
Value: "high"
// Normal priority path
Property: msg.payload.priority
Operator: not equals
Value: "high"Data Quality Control
// Valid data
Expression: msg.payload && msg.payload.id && msg.payload.timestamp
Expected Result: true
// Invalid data
Expression: !msg.payload || !msg.payload.id
Expected Result: trueAdvanced Filtering
Complex Expressions
Use JavaScript expressions for sophisticated filtering:
// Filter based on multiple conditions
Expression: msg.payload.user.role === "admin" || msg.payload.urgent === true;
// Filter based on calculations
Expression: msg.payload.score / msg.payload.maxScore > 0.8;
// Filter based on date/time
Expression: new Date(msg.payload.timestamp) > new Date("2024-01-01");Dynamic Filtering
Modify filter behavior based on runtime conditions:
// Use context for dynamic filtering
Expression: msg.payload.category === flow.get("activeCategory");
// Use environment variables
Expression: msg.payload.environment === env.get("CURRENT_ENV");State-Based Filtering
Filter based on flow state:
// Filter based on processing state
Expression: flow.get("processing") === false;
// Filter based on user session
Expression: flow.get("userSession") === msg.payload.userId;Tips
- Use Clear Conditions: Write filter conditions that are easy to understand
- Test Edge Cases: Verify filter behavior with various input data
- Consider Performance: Complex expressions may impact performance
- Document Logic: Clearly document complex filter conditions
- Use Multiple Filters: Chain filters for complex logic instead of one complex filter
- Handle Errors: Consider what happens when filter expressions fail
Common Issues
Undefined Properties
Handle cases where properties don't exist:
// BAD: This will fail if property doesn't exist
Property: msg.payload.user.name;
Operator: equals;
Value: "admin";
// GOOD: Check for existence first
Expression: msg.payload.user && msg.payload.user.name === "admin";Type Mismatches
Be aware of data type differences:
// BAD: String vs number comparison
Property: msg.payload.id;
Operator: equals;
Value: 123;
// GOOD: Convert types if needed
Expression: parseInt(msg.payload.id) === 123;Performance Issues
Avoid expensive operations in filter expressions:
// BAD: Expensive operation in filter
Expression: msg.payload.data.split(",").length > 10
// GOOD: Use simple property checks when possible
Property: msg.payload.itemCount
Operator: greater than
Value: 10