具有异步数据库读取功能的 DialogFlow Firebase Cloud Function

Question

I am using Firebase Cloud Function as fulfilment for my DialogFlow Google Assistant Action, but I need to retrieve data from the Firebase Database before I manage the intent. Here's a code snippet:

  var userDataRef = sessionDatabaseRef.child(sessionId);
  userDataRef.once("value").then(function(data) {
    console.log(data.val());
    handleIntentAndProcessResponse();
  }).catch(function(){
    console.log("No data yet for this session");
    handleIntentAndProcessResponse();
  });

The function called handleIntentAndProcessResponse is where the intent logic returns the response by setting the conv.ask(new SimpleResponse(blah)) stuff. When I test this it fails and the Cloud Function log gives me this error:

Error: No response has been set. Is this being used in an async call that was not returned as a promise to the intent handler?

So, how can I handle this async call to the Firebase database so it waits for the response? I need to use the data it returns when I handle the intent.

Answer 1

As the error message suggests, you need to return the Promise itself so the dispatcher knows it needs to wait for every part of the async operation to be completed.

Fortunately, the calls to userDataRef.once().then().catch() will evaluate to a Promise, and you can just return this. So this should be good

  return userDataRef.once("value").then(function(data) {
    console.log(data.val());
    handleIntentAndProcessResponse();
  }).catch(function(){
    console.log("No data yet for this session");
    handleIntentAndProcessResponse();
  });