Executing 3 asynchronous operations (where the 2nd one depends of a condition) - breeze

Question

I am working on a durandal / breeze project.
I need to perform several things in my activate function. Thanks to promises I am able to chain asynchronous operations. Please note that I'm still a beginner with all these things so don't hesitate to correct my code.
I have the following activate function inside my viewModel:
var activate = function (routeData) {
initLookups()
var idTran = parseInt(routeData.idTran);
var idItin = parseInt(routeData.idItin);
return datacontext.getTransportById(idTran, transport)
.then(function () { return datacontext.getItineraryById(idItin, itinerary); });
}
So in the return statement:
I fill the transport observable thanks to getTransportById
then I fill the itinerary observable thanks to getItineraryById
-
So far so good. This code works and do his job as expected (maybe not optimised). Now I need to insert a condition between these 2 operations for the case of creating a new entity (if idItin==-1). In this case, a new entity is created. I try with the code below but it doesn't work: I mean the promise doesn't seems to do his job here and thus the view is displayed without waiting for the asynchronous operations to complete.
var activate = function (routeData) {
initLookups()
var idTran = parseInt(routeData.idTran);
var idItin = parseInt(routeData.idItin);
return datacontext.getTransportById(idTran, transport)
.then(function () { if (idItin == -1) return datacontext.createItineraryDetailTransport(idTran); })
.then(function () { return datacontext.getItineraryById(idItin, itinerary); });
}
And below is the createItineraryDetailTransport function of the datacontext:
var createItineraryDetailTransport = function (idTransport) {
var initialValues = ({
transportId: idTransport
});
var newItinerary = manager.createEntity(entityNames.itinerary, initialValues);
return manager.addEntity(newItinerary);
}
So does someone have an idea how to code this thing?

Answer 1

I think that the rigth way is:
return datacontext.getTransportById(idTran, transport).then(function () {
return datacontext.getItineraryById(idItin, itinerary).then(function(){
if (idItin == -1) return datacontext.createItineraryDetailTransport(idTran);
//You have to return something different tu null,false,undefined... or a promise
return true;
);
});
Also, if there is not needed to do this calls sequently, you can do in parallel using Q library (https://github.com/kriskowal/q). The solution could be:
if(idItin ==-1){
//CreateItineraryDetailTransport don't return a promise.
//You can call that like a normal methond.
//It is not a asyncronous methond
datacontext.createItineraryDetailTransport(idTran);
}
return Q.all([datacontext.getTransportById(idTran, transport),datacontext.getItineraryById(idItin, itinerary)]);
-----EDIT-----
Solution doing the creation between the two other calls:
return datacontext.getTransportById(idTran, transport).then(function () {
if (idItin == -1) return datacontext.createItineraryDetailTransport(idTran).then(function(){
return datacontext.getItineraryById(idItin, itinerary);
});
return datacontext.getItineraryById(idItin, itinerary)
});
// I am using Q to do this method return a promise
var createItineraryDetailTransport = function (idTransport) {
var deferred = Q.defer();
var initialValues = ({
transportId: idTransport
});
var newItinerary = manager.createEntity(entityNames.itinerary, initialValues);
manager.addEntity(newItinerary);
deferred.resolve(true);
return deferred.promise;
}
Also you can use Q.fcall:
return Q.fcall(function(){ datacontext.createItineraryDetailTransport(idTran);};
I think that maybe, you don't need to do createItineraryDetailTransport return a promise. Maybe this solution is also possible:
return datacontext.getTransportById(idTran, transport).then(function () {
if (idItin == -1) datacontext.createItineraryDetailTransport(idTran);
return datacontext.getItineraryById(idItin, itinerary);
});