Support Clojure native workflow registrations

[dangdennis]

Today, the usage of Java decorators excludes an easy API for Clojure wrappers to define their own workflows and steps in pure Clojure.

As a workaround, I have had to define workflows and steps in Java and call Clojure business logic within the Java workflows. And then wrap the Java workflows with my own Clojure code. It’s not the best experience.

Ideally I can define Clojure workflows like how Typescript and Go can with their registerWorkflow and registerStep equivalent APIs.

[devhawk]

FYI, #382 improves the DBOSIntegration api for registering and retrieving workflows (it already had a method to start a registered workflow).

According to my coding assist, to use this from Clojure you need a Java helper class and a Clojure function.
Note, I am NOT a clojure developer and I have NOT tested this.

Java Helper

public class ClojureWorkflowAdapter {
    private final IFn fn;
    public ClojureWorkflowAdapter(IFn fn) { this.fn = fn; }
    public Object run(Object[] args) throws Exception {
        return fn.applyTo(RT.arrayToList(args));
    }
}

Clojure wrapper function:

(defn register-workflow
    [f workflow-name class-name]
    (let [adapter (ClojureWorkflowAdapter. f)
          method  (.getDeclaredMethod (class adapter) "run"
                                      (into-array Class [(class (object-array 0))]))
          reg-wf  (.registerWorkflow (DBOS/integration)
                                     workflow-name class-name nil
                                     adapter method nil nil)]
    (fn [& args]
        (-> (.startRegisteredWorkflow (DBOS/integration) reg-wf (object-array args) nil)
            .getResult))))

Usage in clojure:

;; unwrapped workflow method
(defn process-order [order-id amount] ...)

;; wrapped workflow method (called pre DBOS.launch())
(def wf-process-order
    (register-workflow process-order "process-order" "myapp.orders"))

;; invoke wrapped workflow method (called post DBOS.launch())
(durable-process-order order-id amount)

[devhawk]

Not ready for prime time yet, but claude ported the DBOS starter to clojure for me. It's using the less-than-optimal 0.8.0 registration API. https://github.com/dbos-inc/dbos-demo-apps/tree/devhawk/clojure-dbos-starter/clojure/dbos-starter

[devhawk]

FYI, if you target a milestone 0.9.0 release, the register-workflow methods simplifies to this:

(defn register-workflow
  [^DBOS dbos workflow-name f arity]
  (let [param-types (into-array Class (repeat arity Object))
        ifn-invoke  (.getMethod clojure.lang.IFn "invoke" param-types)
        class-name  (.getName (.getClass f))
        reg-wf      (.registerWorkflow (.integration dbos) workflow-name class-name nil f ifn-invoke nil nil)]
    (fn [task-id & args]
      (.getResult (.startRegisteredWorkflow (.integration dbos)
                                            reg-wf
                                            (object-array args)
                                            (StartWorkflowOptions. task-id))))))

[devhawk]

Note, we published the clojure dbos starter demo app https://github.com/dbos-inc/dbos-demo-apps/tree/main/clojure/dbos-starter. The demo app uses a DBOS 0.9 milestone build to pick up the DBOSIntegration improvements.

I'm going to leave this issue open to track official support for Clojure