错误：agent.add() 函数不起作用，即无法向用户获取输出值。在 Google 助手中

Question

Following code is working. But agent.add() function is not working, ie not getting output value to user.

var ref = admin.database().ref().child("Table/"); 
var query = ref.orderByChild("RegId").equalTo(RegId.toString()); 
query.once("value", function(snapshot) { snapshot.forEach(function(child) {
  console.log(child.key);
  console.log("FirstName: " + child.val().FirstName); 
  console.log("Mobile: " + child.val().MobileNumber); 
  console.log("Email: " + child.val().EmailId);
  var name = snapshot.child("FirstName").val(); 
  agent.add(The student name is ` `+` name);`
});

agent.add() is not working but, console.log() is working fine in database logs.

Answer 1

While agent.add() does have some syntax problems in it, that isn't the core of your problem.

You also seem to be getting a child of the snapshot called "FirstName" each time you go through the loop, which I don't think is what you want to do. But this also isn't the core of the problem.

The issue is that query.once() is an asynchronous call, and you're using a callback function to handle it. The Actions on Google library expects you to return a Promise to indicate you are making asynchronous function calls, so it knows not to return anything to the user until the call is completed.

The best way for you to do this is to have query.once() return a Promise, handle your processing in the .then() portion of the Promise, and to return the Promise/then chain in your handler.

I haven't tested it, but it might look something like this:

return query.once("value")
  .then( snapshot => {
    snapshot.forEach( child => {
      let name = child.val().FirstName;
      console.log( 'FirstName: ' + name );
      agent.add( 'The student name is ' + name );
    });
  });

Answer 2

This line has invalid syntax:

agent.add(The student name is ` `+` name);`

Should be quoted properly:

agent.add('The student name is ' + name);
// or if you're using es6:
agent.add(`The student name is ${name}`);

Look into a good code editor that highlights these errors for you. I use vscode.