Chaining multiple chained promises with Q (loopback app) - node.js

Question

Here is a scenario, I've implemented a loopback remote method which imports some data from REST connector to local postgresql connector.
I can do this for a single model
var importData = function (model, cb) {
migrateModel(model, cb)
.then(findImportInfo)
.then(fetchRemoteData)
.then(processFetchedData)
.then(updateImportInfo)
.then(countLocalData)
.then(importCompleted)
.catch(function (err) {
importFailed(err, cb);
})
.done(function () {
console.log('done');
});
};
So the chain does many thing and at the end importCompleted calls the provide cb which is the callback that returns the response to the REST API.
But I can't figure how to do this with multiple models and return each result. I tried something like this, it works actually but REST API never receives a result.
var importDataAll = function (app, cb) {
var models = app.models();
var deferred = Q.defer();
var promises = [];
var results = [];
function doCallback() {
cb(null, results);
}
models.forEach(function (model) {
if (typeof model.importData === 'function') {
migrateModel(model, model.definition.name, null)
.then(findImportInfo)
.then(fetchRemoteData)
.then(processFetchedData)
.then(updateImportInfo)
.then(countLocalData)
.then(function (prevResult) {
var deferred = Q.defer();
var remoteCount = prevResult.dataCount;
var localCount = prevResult.recordCount;
var result =
{
'time': new Date(),
'remoteCount': remoteCount,
'localCount': localCount,
'started': prevResult.started,
'completed': new Date()
}
results.push(result);
deferred.resolve(result);
return deferred.promise;
})
.catch(function (err) {
promises.reject(err);
})
}
});
return Q.allSettled(promises).then(doCallback);
};
I'm lost at that point, any ideas?
EDIT
Trying #Otze's answer I tried this also
var importDataAll = function (app, cb) {
var models = app.models().filter(function (element, index, array) {
return typeof element.importData === 'function';
});
var promises = models.map(function (model) {
migrateModel(model, model.definition.name, null)
.then(findImportInfo)
.then(fetchRemoteData)
.then(processFetchedData)
.then(updateImportInfo)
.then(countLocalData)
.then(importResult)
.catch(function (err) {
promises.reject(err);
})
});
Q.all(promises)
.then(function (resolvedPromises) {
cb(null, results);
});
};
But the result is the same, cb gets called early but the code actually runs in order. I just can't get the result to the response. I think it's never ends so the REST API gets no content after some time.

Answer 1

Have a look at Q.all or any of the other promise combination functions:
http://documentup.com/kriskowal/q/#combination
With Q.all you could do somehting like this:
var promises = myModels.map(doAllThePromiseThings);
Q.all(promises)
.then(function(resolvedPromises) {
doStuff();
});
Note that you need to return a promise from doAllThePromiseThings.
Since .then returns a promise you can simply do:
.then(function (prevResult) {
return {
'time': new Date(),
'remoteCount': prevResult.dataCount,
'localCount': prevResult.recordCount,
'started': prevResult.started,
'completed': new Date()
};
})
instead of
.then(function (prevResult) {
var deferred = Q.defer();
var remoteCount = prevResult.dataCount;
var localCount = prevResult.recordCount;
var result =
{
'time': new Date(),
'remoteCount': remoteCount,
'localCount': localCount,
'started': prevResult.started,
'completed': new Date()
}
results.push(result);
deferred.resolve(result);
return deferred.promise;
})

Answer 2

I use bluebird library's map method to accomplish such use cases:
https://github.com/petkaantonov/bluebird/blob/master/API.md#mapfunction-mapper--object-options---promise
var Promise = require('bluebird');
var importDataAll = function (app, cb) {
var models = app.models().filter(function (element, index, array) {
return typeof element.importData === 'function';
});
Promise.map(
models,
function(model) {
return migrateModel(model, model.definition.name, null) // don't want to break the promise chain
.then(findImportInfo)
.then(fetchRemoteData)
.then(processFetchedData)
.then(updateImportInfo)
.then(countLocalData)
.then(importResult)
.then(function(){
...
return Promise.resolve(); // don't want to break the promise chain
});
},
{concurrency: 1}
)
.then(function () {
debug('finished working on all the models one-by-one');
cb(null);
})
.catch(function (err) {
cb(err);
});