# Validation Function
The `validation` function evaluates rules against message data and collects validation errors.
## Overview
The validation function:
- Evaluates JSONLogic rules against message context
- Collects errors for failed validations
- Is read-only (doesn't modify message data)
- Returns status 200 (pass) or 400 (fail)
## Basic Usage
```json
{
"function": {
"name": "validation",
"input": {
"rules": [
{
"logic": {"!!": {"var": "data.email"}},
"message": "Email is required"
},
{
"logic": {">": [{"var": "data.age"}, 0]},
"message": "Age must be positive"
}
]
}
}
}
```
## Configuration
| Field | Type | Required | Description |
|-------|------|----------|-------------|
| `rules` | array | Yes | List of validation rules |
### Rule Object
| Field | Type | Required | Description |
|-------|------|----------|-------------|
| `logic` | JSONLogic | Yes | Expression that must evaluate to `true` |
| `message` | string | No | Error message (default: "Validation failed") |
## How Validation Works
1. Each rule's `logic` is evaluated against the message context
2. If the result is exactly `true`, the rule passes
3. Any other result (false, null, etc.) is a failure
4. Failed rules add errors to `message.errors`
## Common Validation Patterns
### Required Field
```json
{
"logic": {"!!": {"var": "data.email"}},
"message": "Email is required"
}
```
### Numeric Range
```json
{
"logic": {"and": [
{">=": [{"var": "data.age"}, 18]},
{"<=": [{"var": "data.age"}, 120]}
]},
"message": "Age must be between 18 and 120"
}
```
### String Length
```json
{
"logic": {">=": [
{"length": {"var": "data.password"}},
8
]},
"message": "Password must be at least 8 characters"
}
```
### Pattern Matching (with Regex)
```json
{
"logic": {"regex_match": [
{"var": "data.email"},
"^[^@]+@[^@]+\\.[^@]+$"
]},
"message": "Invalid email format"
}
```
### Conditional Required
```json
{
"logic": {"or": [
{"!": {"var": "data.is_business"}},
{"!!": {"var": "data.company_name"}}
]},
"message": "Company name required for business accounts"
}
```
### Value in List
```json
{
"logic": {"in": [
{"var": "data.status"},
["active", "pending", "suspended"]
]},
"message": "Invalid status value"
}
```
## Multiple Rules
All rules are evaluated, collecting all errors:
```json
{
"rules": [
{
"logic": {"!!": {"var": "data.name"}},
"message": "Name is required"
},
{
"logic": {"!!": {"var": "data.email"}},
"message": "Email is required"
},
{
"logic": {">": [{"var": "data.amount"}, 0]},
"message": "Amount must be positive"
}
]
}
```
## Accessing Errors
After processing, check `message.errors`:
```rust
for error in &message.errors {
println!("{}: {}", error.code, error.message);
}
```
Error structure:
- `code`: "VALIDATION_ERROR" for failed rules
- `message`: The error message from the rule
## Try It
> **Want more features?** Try the [Full Debugger UI](/dataflow-rs/debugger/) with step-by-step execution and workflow visualization.
<div class="playground-widget" data-workflows='[{"id":"validation_demo","name":"Validation Demo","tasks":[{"id":"parse","name":"Parse Payload","function":{"name":"parse_json","input":{"source":"payload","target":"input"}}},{"id":"validate","name":"Validate","function":{"name":"validation","input":{"rules":[{"logic":{"!!":[{"var":"data.input.email"}]},"message":"Email is required"},{"logic":{">":[{"var":"data.input.age"},0]},"message":"Age must be positive"},{"logic":{"in":[{"var":"data.input.status"},["active","pending","suspended"]]},"message":"Invalid status"}]}}}]}]' data-payload='{"name":"John","age":0,"status":"unknown"}'>
</div>
Notice the validation errors in the output.
## Validation with Continue on Error
Combine validation with data transformation:
```json
{
"id": "validated_transform",
"continue_on_error": true,
"tasks": [
{
"id": "validate",
"function": {
"name": "validation",
"input": {
"rules": [...]
}
}
},
{
"id": "transform",
"function": {
"name": "map",
"input": {
"mappings": [...]
}
}
}
]
}
```
With `continue_on_error: true`, transformation proceeds even if validation fails.
## Stop on Validation Failure
For strict validation (stop on failure):
```json
{
"continue_on_error": false,
"tasks": [
{
"id": "validate",
"function": {"name": "validation", "input": {...}}
},
{
"id": "process",
"function": {"name": "map", "input": {...}}
}
]
}
```
If validation fails, subsequent tasks are skipped.
## Best Practices
1. **Validate Early** - Add validation as the first task
2. **Clear Messages** - Write specific, actionable error messages
3. **Check All Rules** - Validation evaluates all rules (doesn't short-circuit)
4. **Use continue_on_error** - Decide if processing should continue on failure
5. **Handle Errors** - Always check `message.errors` after processing