using bluebird promises with express to make API calls

Question

I'm trying to get different chunks of data from a trello API using bluebird promises library. In my express router I'm using middleware isLoggedIn, and getBoards, which body looks something like:

trello.get("/1/members/me/boards") // resolves with array of board objects
 .each((board) => {
  // do some async stuff like saving board to db or other api calls, based on retrieved board
 .catch(err => console.error('ERR: fetching boards error - ${err.message}'))
 })

The question is: I want to redirect (res.redirect('/')) only when all boards were retrieved and saved. How can I do that? Where should I place xres.redirect('/') expression?

Answer 1

I think you need something like:

    var Promise = require('bluebird'); 
    var promises = [];
    trello.get("/1/members/me/boards") // resolves with array of board objects
 .each((board) => {
  // 
  promises.push( /*some promisified async call that return a promise, saving data in db or whatever asynchronous action. The important bit is that this operation must return a Promise.  */  );
 });
 //So now we have an array of promises. The async calls are getting done, but it will take time, so we work with the promises: 

 Promise.all(promises).catch(console.log).then( function(results){
      /*This will fire only when all the promises are fullfiled. results is an array with the result of every async call to trello. */
     res.redirect('/'); //now we are safe to redirect, all data is saved
 } );

EDIT:

Actually, you can avoid some boilerplate code using map instead of each:

trello.get("/1/members/me/boards") // resolves with array of board objects
.map((board) => {
    return somePromisifiedSaveToDbFunction(board);
}).all(promises).catch(console.log).then( function(results){
 res.redirect('/'); 
} );