Validation in custom block implementation

Harald_Meyer · July 17, 2025, 7:57am

Hi,

I have a custom block that reads some of its configuration from tenant options. So far, I have implemented this in the $init action:

    action $init() {
		monitor.subscribe(FindTenantOptionsResponse.SUBSCRIBE_CHANNEL);
		FindTenantOptions tenantOptionRequest := new FindTenantOptions;
		tenantOptionRequest.reqId := Util.generateReqId();
		tenantOptionRequest.category := "...";
		on FindTenantOptionsResponse(reqId = tenantOptionRequest.reqId) as tor {
			monitor.unsubscribe(FindTenantOptionsResponse.SUBSCRIBE_CHANNEL);

		}
		send tenantOptionRequest to FindTenantOptions.SEND_CHANNEL;
    }

But I would like to properly handle cases where these tenant options are not set. I could move the logic to $validate but the problem is that because I receive the tenant options in a listener, the $validate action will already have terminated successfully.

How should I do this best?

Mario_Heidenreich2 · July 17, 2025, 8:19am

Hey Harald, did you have a look at the async Validation:

github.com/Cumulocity-IoT/apama-analytics-builder-block-sdk

doc/110-AsynchronousValidations.md

main

# Asynchronous validations

Typically, a block will perform validation synchronously. By the time the action call to `$validate` is complete, the action has either thrown an exception due to an error or the action has checked that the block is in a valid state. There are cases, however, where an external lookup needs to be completed, typically by sending a request to another monitor or component external to the correlator which will later send a response. EPL does not permit an action call to block until this is complete, as this is (potentially) external to the correlator, and would block processing of other events while waiting for a response. To permit this pattern, the `$validate` call may be declared to return a `Promise` value. A `Promise` is a type that indicates future completion (or failure). If the `$validate` call returns a `Promise` object, validating the model will be suspended until the `Promise` is fulfilled, and the framework will not start executing the model until all validation steps have been completed. While `Promise` may yield a return value, for `$validate`, the value on completion should always be an empty `any` value.

A `Promise` should be completed within a reasonable amount of time. By default, the framework will wait for 60 seconds for the `Promise` to complete. If the `Promise` is not completed within the timeout duration, then the model deployment fails. The timeout duration can be changed via a tenant option. The framework also logs a warning if a `Promise` takes more than 10 seconds to complete. Refer to the Streaming Analytics guide for more details.

A `Promise` is typically created with the `Promise.create` method. This takes an action which has two callback actions as parameters - for success and failure. Alternatively, `Promise.resolve` will return a `Promise` which is already resolved (unless the value passed to `resolve` is itself a `Promise` which is not fulfilled). A simplified example:

```Java
action $validate() returns Promise {
    if (needsLookup()) {
        return Promise.create(lookup);
    } else {
        return Promise.resolve(new any); // empty any 'return' value
    }
}

action lookup(action<any> success, action<Exception> failure) {
    integer id := integer.getUnique();
    send LookupRequest(id) to LookupRequest.CHANNEL;

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Harald_Meyer · July 17, 2025, 9:56am

This is working. Thank you!

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Validation in custom block implementation

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