Conditions

Pre-handler functions the engine evaluates before executing a trigger — if the condition returns false, the handler function is not called.

Conditions are regular iii functions that the engine calls before a trigger's handler runs. Attach a condition to any trigger by adding the condition function's ID to the trigger config. If the condition returns false, the handler function is not called.

Condition functions are registered with registerFunction / register_function like any other function. They receive the same event data as the handler and must return a boolean.

HTTP trigger condition

The condition function receives the full API request. If it returns false, the engine responds with 422 Unprocessable Entity and the handler function is not called.

import { registerWorker, Logger, TriggerAction } from 'iii-sdk'

const iii = registerWorker(process.env.III_URL ?? 'ws://localhost:49134')

iii.registerFunction(
  { id: 'conditions::is_premium' },
  async (req: ApiRequest<{ amount: number }>) => {
    return (req.body?.amount ?? 0) > 1000
  },
)

iii.registerFunction(
  { id: 'orders::premium', description: 'Processes premium orders' },
  async (req: ApiRequest<{ amount: number; description: string }>) => {
    const logger = new Logger()
    logger.info('Processing premium order', { amount: req.body?.amount })
    return { status_code: 200, body: { message: 'Premium order processed' } }
  },
)

iii.registerTrigger({
  type: 'http',
  function_id: 'orders::premium',
  config: {
    api_path: 'orders/premium',
    http_method: 'POST',
    condition_function_id: 'conditions::is_premium',
  },
})

from iii import register_worker, InitOptions, ApiRequest, ApiResponse, Logger, TriggerAction

iii = register_worker(address="ws://localhost:49134", options=InitOptions(worker_name="orders-worker"))

def is_premium(data) -> bool:
    req = ApiRequest(**data) if isinstance(data, dict) else data
    return (req.body or {}).get("amount", 0) > 1000

def orders_premium(data) -> ApiResponse:
    logger = Logger()
    req = ApiRequest(**data) if isinstance(data, dict) else data
    logger.info("Processing premium order", {"amount": (req.body or {}).get("amount")})
    return ApiResponse(status_code=200, body={"message": "Premium order processed"})

iii.register_function({"id": "conditions::is_premium"}, is_premium)
iii.register_function({"id": "orders::premium"}, orders_premium)

iii.register_trigger({
    "type": "http",
    "function_id": "orders::premium",
    "config": {
        "api_path": "orders/premium",
        "http_method": "POST",
        "condition_function_id": "conditions::is_premium",
    },
})

use iii_sdk::{register_worker, InitOptions, Logger, TriggerRequest, TriggerAction, RegisterFunctionMessage, RegisterTriggerInput};
use serde_json::json;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let iii = register_worker("ws://127.0.0.1:49134", InitOptions::default());

    iii.register_function(RegisterFunctionMessage { id: "conditions::is_premium".into(), ..Default::default() }, |input| async move {
        let amount = input["body"]["amount"].as_f64().unwrap_or(0.0);
        Ok(json!(amount > 1000.0))
    });

    iii.register_function(RegisterFunctionMessage { id: "orders::premium".into(), ..Default::default() }, |input| async move {
        let logger = Logger();
        let amount = input["body"]["amount"].as_f64().unwrap_or(0.0);
        logger.info("Processing premium order", Some(json!({ "amount": amount })));
        Ok(json!({ "status_code": 200, "body": { "message": "Premium order processed" } }))
    });

    iii.register_trigger(RegisterTriggerInput { type_: "http".into(), function_id: "orders::premium".into(), config: json!({
        "api_path": "orders/premium",
        "http_method": "POST",
        "condition_function_id": "conditions::is_premium",
    }), ..Default::default() })?;

    loop { tokio::time::sleep(std::time::Duration::from_secs(60)).await; }
}

Queue trigger condition

The condition function receives the queue message data. If it returns false, the handler function is not called — no error is raised.

iii.registerFunction(
  { id: 'conditions::is_high_value' },
  async (data: { amount: number }) => {
    return data.amount > 1000
  },
)

iii.registerFunction(
  { id: 'orders::high_value', description: 'Processes high-value orders from queue' },
  async (data: { amount: number; description: string }) => {
    const logger = new Logger()
    logger.info('Processing high-value order', { amount: data.amount })

    await iii.trigger({
      function_id: 'enqueue',
      payload: { topic: 'order.processed', data: { ...data, processedAt: new Date().toISOString() } },
      action: TriggerAction.Void(),
    })
  },
)

iii.registerTrigger({
  type: 'queue',
  function_id: 'orders::high_value',
  config: { topic: 'order.created', condition_function_id: 'conditions::is_high_value' },
})

from datetime import datetime, timezone
from iii import Logger

def is_high_value(data) -> bool:
    if isinstance(data, dict):
        return data.get("amount", 0) > 1000
    return False

def orders_high_value(data: dict) -> None:
    logger = Logger()
    amount = data.get("amount", 0)
    logger.info("Processing high-value order", {"amount": amount})

    if amount <= 1000:
        logger.info("Low-value order — skipping", {"amount": amount})
        return

    iii.trigger({
        "function_id": "enqueue",
        "payload": {"topic": "order.processed", "data": {**data, "processedAt": datetime.now(timezone.utc).isoformat()}},
        "action": TriggerAction.Void(),
    })


iii.register_function({"id": "conditions::is_high_value"}, is_high_value)
iii.register_function({"id": "orders::high_value"}, orders_high_value)

iii.register_trigger({
    "type": "queue",
    "function_id": "orders::high_value",
    "config": {"topic": "order.created", "condition_function_id": "conditions::is_high_value"},
})

use iii_sdk::{Logger, TriggerRequest, TriggerAction, RegisterFunctionMessage, RegisterTriggerInput};
use serde_json::json;

iii.register_function(RegisterFunctionMessage { id: "conditions::is_high_value".into(), ..Default::default() }, |input| async move {
    let amount = input["amount"].as_f64().unwrap_or(0.0);
    Ok(json!(amount > 1000.0))
});

iii.register_function(RegisterFunctionMessage { id: "orders::high_value".into(), ..Default::default() }, |input| async move {
    let logger = Logger();
    let amount = input["amount"].as_f64().unwrap_or(0.0);
    logger.info("Processing high-value order", Some(json!({ "amount": amount })));

    iii.trigger(TriggerRequest::new("enqueue", json!({
        "topic": "order.processed",
        "data": { "amount": amount, "processedAt": chrono::Utc::now().to_rfc3339() },
    })).action(TriggerAction::void())).await?;

    Ok(json!(null))
});

iii.register_trigger(RegisterTriggerInput { type_: "queue".into(), function_id: "orders::high_value".into(), config: json!({
    "topic": "order.created",
    "condition_function_id": "conditions::is_high_value",
}), ..Default::default() })?;

State trigger condition

The condition receives the full state event, including the event type (created, updated, deleted), scope, key, and both old and new values.

iii.registerFunction(
  { id: 'conditions::is_update' },
  async (event: { event_type: string; scope: string; key: string; old_value: unknown; new_value: unknown }) => {
    return event.event_type === 'updated'
  },
)

iii.registerFunction(
  { id: 'orders::on_update', description: 'Reacts to order state updates' },
  async (event) => {
    const logger = new Logger()
    logger.info('Order updated', { scope: event.scope, key: event.key })
  },
)

iii.registerTrigger({
  type: 'state',
  function_id: 'orders::on_update',
  config: { scope: 'orders', condition_function_id: 'conditions::is_update' },
})

from iii import Logger

def is_update(event) -> bool:
    if isinstance(event, dict):
        return event.get("event_type") == "updated"
    return False

def orders_on_update(event: dict) -> None:
    logger = Logger()
    logger.info("Order updated", {"scope": event.get("scope"), "key": event.get("key")})

iii.register_function({"id": "conditions::is_update"}, is_update)
iii.register_function({"id": "orders::on_update"}, orders_on_update)

iii.register_trigger({
    "type": "state",
    "function_id": "orders::on_update",
    "config": {"scope": "orders", "condition_function_id": "conditions::is_update"},
})

use iii_sdk::{Logger, RegisterFunctionMessage, RegisterTriggerInput};
use serde_json::json;

iii.register_function(RegisterFunctionMessage { id: "conditions::is_update".into(), ..Default::default() }, |input| async move {
    let event_type = input["event_type"].as_str().unwrap_or("");
    Ok(json!(event_type == "updated"))
});

iii.register_function(RegisterFunctionMessage { id: "orders::on_update".into(), ..Default::default() }, |input| async move {
    let logger = Logger();
    logger.info("Order updated", Some(json!({
        "scope": input["scope"],
        "key": input["key"],
    })));
    Ok(json!(null))
});

iii.register_trigger(RegisterTriggerInput { type_: "state".into(), function_id: "orders::on_update".into(), config: json!({
    "scope": "orders",
    "condition_function_id": "conditions::is_update",
}), ..Default::default() })?;

Key concepts

Condition functions are registered with registerFunction / register_function like any other function. They receive the same event data as the handler and must return true or false.
Add condition_function_id to the trigger config with the condition function's ID. This key is the same for all trigger types.
When a condition returns false:
- HTTP — the engine responds with 422 Unprocessable Entity; the handler function is not called.
- Queue / Cron — the handler function is not called; no error is surfaced.
- State / Stream — the handler function is not called.
If a condition function errors, the engine logs the error and does not call the handler (HTTP returns 500 Internal Server Error).
A single condition function can be shared across multiple triggers.

HTTP trigger condition

Queue trigger condition

State trigger condition

Key concepts

On this page