forEach using generators in Node.js

node.js foreach mongoose generator koa

Mazhar Ahmed · Jul 16, 2014 · Viewed 26.3k times · Source

I'm using Koa.js framework and Mongoose.js module.

Normally to get a result from MongoDB I code like this:

var res = yield db.collection.findOne({id: 'my-id-here'}).exec();

But I need to execute this line for every element of an array named 'items'.

items.forEach(function(item) {
  var res = yield db.collection.findOne({id: item.id}).exec();
  console.log(res)  // undefined
});

But this code doesn't run as yield is in the function. If I write this:

items.forEach(function *(item) {
  var res = yield db.collection.findOne({id: item.id}).exec();
  console.log(res)  // undefined
});

I'm not getting the result in res variable either. I tried to use 'generator-foreach' module but that didn't worked like this.

I know that this is my lack of knowledge about the language literacy of Node.js. But can you guys help me finding a way how to do this?

Answer

You can yield arrays, so just map your async promises in another map

var fetchedItems = yield items.map((item) => {
   return db.collection.findOne({id: item.id});
});