I have a service with a method that gets me a list of project types using a $resource. It's working well for me, except that if I make multiple nearly simultaneous calls (from say, two directives) each will create another request instead of using the same response/$promise/data.
I found this which led me to this and TL;DR, apparently it's creating a redundant $q.defer() and is actually considered to be a deferred anti-pattern.
The code below works well if the calls to get project types are significantly staggered (like more than milliseconds apart). The consecutive calls are resolved with the shared.projectTypes. It also works in the sense that if the request to get project types fails, the dfr.reject() will be triggered and be caught by .catch in the calling controller.
angular.module('projects')
.factory('projectService', function(notificationService){
// an object to share data gathered by this service
var shared = {};
// $resource for projects API
var projectResource = $resource(baseApiPath + 'projects', {}, {
...,
getProjectTypes: {
method: 'GET',
url: baseApiPath + 'projects/types'
},
...
});
// loads a list of project types
var loadProjectTypes = function(){
var dfr = $q.defer();
// if we've already done this, just return what we have.
if(shared.projectTypes){
dfr.resolve(shared.projectTypes);
}
else {
// begin anti-pattern (?)
projectResource.getProjectTypes(null,
function(response){
shared.projectTypes = response.result.projectTypes;
dfr.resolve(response);
},
function(errResponse){
console.error(errResponse);
notificationService.setNotification('error', errResponse.data.messages[0]);
dfr.reject(errResponse);
});
}
return dfr.promise;
};
return {
shared: shared,
project: projectResource,
loadProjectTypes: loadProjectTypes
};
});
So, I read that having this extra var dfr = $q.defer() is not necessary as the $resource would provide all that for me. With a bit of refactoring, I ended up with this:
...
// $resource for projects API
var projectResource = $resource(baseApiPath + 'projects', {}, {
...,
getProjectTypes: {
method: 'GET',
url: baseApiPath + 'projects/types',
isArray: true,
transformResponse: function(response){
return JSON.parse(response).result.projectTypes;
}
},
...
});
// loads a list of project types
var loadProjectTypes = function(){
return shared.projectTypes || (shared.projectTypes = projectResource.getProjectTypes());
};
...
To clarify, I have added isArray and transformResponse to the resource because my API returns a lot of extra meta information and all I wanted was an array of types. In my loadProjectTypes method, I'm including the same caching we originally had, but I'm caching the result of projectResource.getProjectTypes() instead of the actual response data (even though that might be exactly what I'm caching because of the transformResponse).
This works on the happy path (reduced calls to API, returns the same thing to everyone, etc) but my main problem is with the chaining and catching of errors.
In my original anti-pattern example, if there is an error with GET /project/types, I'm using dfr.reject() which is then passed back to my controller where I have a .catch().
This is code from the controller which actually makes the original request to get project types:
$q.all([
projectService.loadProjects(),
userService.loadUserRole('project_manager'),
userService.loadUserRole('sales_representative'),
projectService.loadProjectTypes(),
clientService.loadClients()
])
.then(function(response){
// doing stuff with response
})
.catch(function(errResponse){
// expecting errors from service to bubble through here
console.error(errResponse);
});
With the anti-pattern example, the dfr.reject is causing the error to show up here in the catch, but in my supposed non-anti-pattern example, it's not happening. I'm not sure how to reject or resolve the $resource results in the same way I was before. If one of the points of promise chaining is to have one spot to handle errors from any chain link, I was doing it right.
I tried to use $q.resolve()/reject(), since I don't have dfr anymore, but this seems dumb and doesn't work anyway.
return shared.projectTypes || (shared.projectTypes = projectResource.getProjectTypes(null,
function(response){
return $q.resolve(response);
},
function(errResponse){
return $q.reject(errResponse);
}));
How do I get the chain to work so that .catch() in the controller is where the errors get handled?
Did I actually implement the anti-pattern in my original code, or was that one of the accepted ways to use $q.defer() and it wasn't an anti-pattern at all?
In the second link I posted, there is an answer that says:
"What's wrong with it? But the pattern works! Lucky you.
Unfortunately, it probably doesn't, as you likely forgot some edge
case. In more than half of the occurrences I've seen, the author has
forgotten to take care of the error handler."
However, my original code was addressing the errors. It was working, except that each caller was getting it's own promise. I feel that's where I missed something.
I might be confused, but I'm thinking that the loadProjectTypes method should return the same promise/data to anyone who calls it, no matter when it's called. It should be the one true source of anything projectTypes and only make the call once, the very first time.
Any time I look for any of this (lots of purple/visited google links on these subjects), everyone is either showing chaining with contrived examples, or only using $http, or something else. I haven't found anyone doing error catching in a promise chain that uses $resource.
UPDATE: Adding my requirements for the solution. I posted them in my answer, but wanted to include them in the original post too.
Requirement 1: Allows multiple calls to the method, but only makes one API request which updates all callers with the same data.
Requirement 2: Must be able to use result of method as actual data, just as the promise spec intends. var myStuff = service.loadStuff() should actually set myStuff to be "stuff".
Requirement 3: Must allow promise chaining so that all errors in any part of the chain can be caught by a single catch at the end of the chain. As I've found in my solution, there can be more than one chain, and more than one catch, but the point is that each chain has a catch, and any "links" in the chain that break should all report their errors to their respective catch.
Isn't that always the way, as soon as you speak your problems, you come across your solution.
Requirement 1: Only make one request per method call. This is solved with the original fix to the anti-pattern. This will either always return the $resource result by either returning the cached $resource or returning and caching at the same time.
var loadProjectTypes = function(){
return shared.projectTypes || (shared.projectTypes = projectResource.getProjectTypes());
};
Requirement 2: Be able to use the service method as a promise where I can set the value of a $scope variable directly to the result of loadProjectTypes(). Using the revised method above, I can simply state $scope.theTypes = projectService.loadProjectTypes() and it'll automatically be filled with the list of types when they come in, just as the promise spec intends.
Requirement 3: Be able to chain together multiple $resource calls and have their errors be caught by a single .catch(). By using the $promise of the result of loadProjectTypes within $q.all(), I can catch any errors in any catch I want.
$q.all([
...,
projectService.loadProjectTypes().$promise,
...
])
.then(function(response){
// my project types comes in as response[n]
})
.catch(function(errResponse){
// but any errors will be caught here
});
Technically, I can put catches in different places and they'll all work the same. Anytime I have loadProjectTypes(), I can use a .catch() and my errors will be handled there. Each loader of types can handle the API being down in it's own way. This could be really good actually. A controller might get the UI to display a message and a small directive might just display something else, or nothing at all. They each can handle the bad in their own way.
My service, directive and controller look like this now:
angular.module('projects')
.factory('projectService', function(notificationService){
// an object to share data gathered by this service
var shared = {};
// $resource for projects API
var projectResource = $resource(baseApiPath + 'projects', {}, {
...,
getProjectTypes: {
method: 'GET',
url: baseApiPath + 'projects/types',
isArray: true,
transformResponse: function(response){
return JSON.parse(response).result.projectTypes;
}
},
...
});
// loads a list of project types
var loadProjectTypes = function(){
return shared.projectTypes || (shared.projectTypes = projectResource.getProjectTypes());
};
return {
shared: shared,
project: projectResource,
loadProjectTypes: loadProjectTypes
};
});
angular.module('projects')
.directive('projectPageHeader', ['projectService', function(projectService){
return {
restrict: 'E',
scope: {
active: '#',
},
templateUrl: 'src/js/apps/projects/partials/dir_projectPageHeader.html',
replace: true,
controller: function($scope){
$scope.projectService = projectService;
// sets the types to the array of types
// as given by the transformResponse
$scope.types = projectService.getProjectTypes();
// could also do a .$promise.catch here if I wanted.
// all catches will fire if get projectTypes fails.
}
};
}]);
angular.module('projects')
.controller('projectListPageController', [
'$scope','projectService',
function($scope, projectService){
// load it all up
$q.all([
projectService.loadProjectDetails($routeParams.projectId).$promise,
userService.loadUserRole('project_manager').$promise,
userService.loadUserRole('sales_representative').$promise,
projectService.loadProjectStatuses().$promise,
projectService.loadProjectTypes().$promise,
clientService.loadClients().$promise
])
.then(function(response){
// do work with any/all the responses
})
.catch(function(errResponse){
// catches any errors from any of the $promises above.
})
}]);
Since the loadProjectTypes (or any other load_____ method) saves the types within the service it comes from, I don't really need to do any storing on the controller. projectService.shared.projectTypes is universal across the entire app. The .then() method in my controller could potentially be noop if all the services were storing the results of their loads internally (which is how I like it) unless there was some view specific thing I needed to do with them. I typically only use controllers for entire pages, or $modals. Everything else is broken up into directives and most information and logic is in services.
I'm leaving the question open in case someone has a better solution. I like the one that Jack A. posted, but I feel it makes my load___ methods more verbose than they already are. Since there are a few of them with slight differences, it leads to a lot of redundant code, or complex 'smart' methods in my actual code. It definitely solves Requirement 1 and possibly 2 and 3 though.
UPDATE (GOTCHA):
So, I've been using this pattern for a few days now and it's working really exactly as I intend. It's really streamlined our process; however, I recently came upon a gotcha when using a method like loadProjectTypes in a singular context (i.e.: outside of $q.all()).
If you just use the load method like so:
// This code is just placed in your controllers init section
loadProjectTypes()
.$promise
.then(function(response){
// ... do something with response (or noop)
})
.catch(function(errResponse){
// ... do something with error
});
You will run into a situation when that controller 'refreshes'. For example, you have the code above in controllerA, you change "pages" which uses controllerB, then you go back to the first "page" and controllerA refreshes and tries to run this again. The error you get is that "there is no .then of undefined."
Inspecting this in the console, the first time loadProjectTypes() runs, it returns the response from the $resource (which includes $promise AND all the projectType data). The second time - coming back from controllerB - it will only hold the projectType data. There is no more $promise because you are not returning the result of a $resource, you returned the cached shared.projectTypes that you set after the first time. That's why we did all this, remember? I'm not sure why this goes away since that's what you saved to shared.projectTypes, but it does, and it doesn't actually matter.
return shared.projectTypes || (shared.projectTypes = projectResource.getProjectTypes());
For me, the easiest fix was to just have loadProjectTypes().$promise as the only member of a $q.all() set:
// again, this code is just placed somewhere near the top of your controller
$q.all([
loadProjectTypes().$promise
])
.then(...)
.catch(...);
In most cases, my controllers will be getting more than one thing so this would've happened eventually, but there will always be a situation where you only need to load one thing. Using a single item set in $q.all() is the only way to have no issues when using this solution. It's not that bad really, could've been worse.
I wrote something very similar to this a while ago, with a couple key differences:
I only create the promise when the data is already in the cache and return the native promise when an actual request is initiated.
I added a third state for when a request for the resource is already pending.
A simplified version of the code looks like this:
module.factory("templateService", function ($templateCache, $q, $http) {
var requests = {};
return {
getTemplate: function getTemplate(key, url) {
var data = $templateCache.get(key);
// if data already in cache, create a promise to deliver the data
if (data) {
var deferred = $q.defer();
var promise = deferred.promise;
deferred.resolve({ data: data });
return promise;
}
// else if there is an open request for the resource, return the existing promise
else if (requests[url]) {
return requests[url];
}
// else initiate a new request
else {
var req = $http.get(url);
requests[url] = req;
req.success(function (data) {
delete requests[url];
$templateCache.put(key, data);
});
return req;
}
},
};
});
Related
I'm trying to mock a response to a JSONP GET request which is made with a function that returns an ES6 promise which I've wrapped in $q.when(). The code itself works just fine, however, in the unit tests the request is not being caught by $httpBackend and goes through right to the actual URL. Thus when flush() is called I get an error stating Error: No pending request to flush !. The JSONP request is made via jQuery's $.getJSON() inside the ES6 promise so I opted to try and catch all outgoing requests by providing a regex instead of a hard-coded URL.
I've been searching all over trying to figure this out for a while now and still have yet to understand what's causing the call to go through. I feel as if the HTTP request in the ES6 promise is being made "outside of Angular" so $httpBackend doesn't know about it / isn't able to catch it, although that may not be the case if the call was being made inside of a $q promise from the get-go. Can anyone possibly tell me why this call is going through and why a simple timeout will work just fine? I've tried all combinations of $scope.$apply, $scope.$digest, and $httpBackend.flush() here, but to no avail.
Maybe some code will explain it better...
Controller
function homeController() {
...
var self = this;
self.getData = function getData() {
$q.when(user.getUserInformation()).then(function() {
self.username = user.username;
});
};
}
Unit Test
...
beforeEach(module('home'));
describe('Controller', function() {
var $httpBackend, scope, ctrl;
beforeEach(inject(function(_$httpBackend_, $rootScope, $componentController) {
$httpBackend = _$httpBackend_;
scope = $rootScope.$new(); // used to try and call $digest or $apply
// have also tried whenGET, when('GET', ..), etc...
$httpBackend.whenJSONP(/.*/)
.respond([
{
"user_information": {
"username": "TestUser",
}
}
]);
ctrl = $componentController("home");
}));
it("should add the username to the controller", function() {
ctrl.getData(); // make HTTP request
$httpBackend.flush(); // Error: No pending request to flush !
expect(ctrl.username).toBe("TestUser");
});
});
...
For some reason this works, however:
it("should add the username to the controller", function() {
ctrl.getData(); // make HTTP request
setTimeout(() => {
// don't even need to call flush, $digest, or $apply...?
expect(ctrl.username).toBe("TestUser");
});
});
Thanks to Graham's comment, I was brought further down a different rabbit hole due to my lack of understanding several things which I will summarize here in case someone ends up in the same situation...
I didn't fully understand how JSONP works. It doesn't rely on XmlHttpRequest at all (see here). Rather than trying to fiddle with mocking responses to these requests through JSONP I simply switched the "debug" flag on the code I was using which disabled JSONP so the calls were then being made via XHR objects (this would fail the same origin policy if real responses were needed from this external API).
Instead of trying to use jasmine-ajax, I simply set a spy on jQuery's getJSON and returned a mock response. This finally sent the mocked response to the ES6 promise, but for some reason the then function of the $q promise object which resulted from wrapping the ES6 promise wasn't being called (nor any other error-handling functions, even finally). I also tried calling $scope.$apply() pretty much anywhere in the off chance it would help, but to no avail.
Basic implementation (in unit test):
...
spyOn($, 'getJSON').and.callFake(function (url, success) {
success({"username": "TestUser"}); // send mock data
});
ctrl.getData(); // make GET request
...
Problem (in controller's source):
// user.getUserInformation() returns an ES6 promise
$q.when(user.getUserInformation()).then(function() {
// this was never being called / reached! (in the unit tests)
});
Ultimately I used #2's implementation to send the data and just wrapped the assertions in the unit test inside of a timeout with no time duration specified. I realize that's not optimal and hopefully isn't how it should be done, but after trying for many hours I've about reached my limit and given up. If anyone has any idea as to how to improve upon this, or why then isn't being called, I would honestly love to hear it.
Unit Test:
...
ctrl.getData(); // make GET request
setTimeout(() => {
expect(ctrl.username).toBe("TestUser"); // works!
});
I have a real problem with JavaScript promises that I've been trying to solve for the last few hours and I just can't seem to fix it. My experience with promises is limited so I'm open to the idea that my approach is simply incorrect.
Right now I'm building an app that requires a two-step process:
Connect to an external PaaS service, which returns a promise
Within that promise, retrieve some data
Here's a sample of a factory I created:
app.factory('serviceFactory', [
function() {
var getData = function getData() {
service.connect(apiKey).then(function() {
service.getData('dataStore').then(function(result) {
// Retrieve data
return result;
}, errorFunction);
},
errorFunction);
};
return {
getData: getData
};
}
]);
As you can see, there are nested promises here. What's causing me problems is when I try to use the data from the most deeply-nested promise within an AngularJS view. Specifically, I want to use the data from that promise in an ng-repeat statement. But no matter what I try, it just won't show up. I've attempted to assign data within the promise instead of returning, like so:
service.getData('dataStore').then(function(result) {
// Retrieve data
// Assigned the enclosing scope's this to 'self'
self.data = result;
}, errorFunction);
That doesn't work either. I've tried a variety of other approaches, but I just can't seem to get that data to the view. There's no problem getting it to show up in a console.log(data)call, so I know the data is coming back correctly. Does anyone have experience solving a problem like this?
I would suggest that you'll try to avoid nested promises. You can take a look at this blog post, which will let you see how you can avoid 'promise soup' and have promise chaining instead.
As for your question, I would recommend the following:
A quick solution will be to fix your problem. You are returning the factory method wrong:
app.factory('serviceFactory', [
function() {
var getData = function getData() {
return service.connect(apiKey).then(function() {
service.getData('dataStore').then(function(result) {
// Retrieve data
return result;
}, errorFunction);
},
errorFunction);
};//here you should close the 'getData method
return {
getData: getData
};
}
]);
But, you can refactor your code to chain your promises. Something like:
app.factory('serviceFactory', [
function() {
var connect = function connect() {
return service.connect(apiKey);
};
var getData = function getData(data) {
return service.getData(data);
};
return {
getData: getData,
connect: connect
};
}
]);
Now, you can do something like this:
serviceFactory.connect(apiKey)
.then(serviceFactory.getData)
.then(function(result){
//use data here
})
All of this should be tested - you can add a plunker or jsbin if you want a working solution...
EDIT
I think that you have another problem here. You are mixing between serviceFactory and service. I'm not sure that I understand if this is the same service, or which is who. Can you provide a more detailed code or add plunker/jsbin etc.
I've edited this answer, which I originally deleted because I didn't explain what I meant very clearly and it garnered some downvotes (without explanation, but that's my guess). Anyway, here is a more complete answer.
I suspect that your problem is that whatever PaaS you are using has no awareness of Angular, and Angular likewise has no awareness of the PaaS. You say in your question that the PaaS has methods that return promises, but if Angular is not aware of those promises, then, when the promises resolve, Angular does not know to update the DOM. Angular does this via the digest cycle which is where Angular checks everything that it is watching to see if it has changed. When using $q (or other Angular services like $http), Angular knows to automatically kick off a digest cycle when they resolve. It does not, however, kick off a digest cycle when promises created by other means resolve.
This is what I think is happening in your code. Your PaaS is giving you promises, which are resolving properly (you said you can see the results via console), but your HTML is not being updated.
I modified the plunkr we were working on to demonstrate this in action. I created a mock PaaS (not knowing what you are using) that creates promises using jQuery and resolves them. As you can see, when the promises resolve, the result is logged to the console, but the DOM is not resolved.
angular.module("app",[])
.value("mockPaaS", mockPaaS)
.factory("dataFactory", function($q, mockPaaS){
function getData(){
return mockPaaS.connect()
.then(mockPaaS.getData);
}
return {
getData: getData
}
})
.controller("DataController", function (dataFactory) {
var vm = this;
dataFactory.getData().then(function(result){
console.log(result);
vm.dataArr = result;
});
})
.directive("myApp", function(){
return {
bindToController: true,
controller: "DataController",
controllerAs: 'myApp',
template: "<div ng-repeat='i in myApp.dataArr'>{{i}}</div>"
};
});
I was originally suggesting that you could solve this problem by adding a $scope.$apply() after you capture the result of the promise. I've forked the Plunker and you can see here it does, in fact update the DOM.
.controller("DataController", function ($scope, dataFactory) {
var vm = this;
dataFactory.getData().then(function(result){
console.log(result);
vm.dataArr = result;
$scope.$apply();
});
})
There is, however, a more idiomatic solution. When you get a promise from outside angular that you need to use in Angular, you can wrap that promise using $q.when (an Angular aware promise), and when the external promise resolves, Angular should kick off it's digest cycle naturally.
.factory("dataFactory", function($q, mockPaaS){
function getData(){
return $q.when(mockPaaS.connect()
.then(mockPaaS.getData));
}
return {
getData: getData
}
})
.controller("DataController", function (dataFactory) {
var vm = this;
dataFactory.getData().then(function(result){
console.log(result);
vm.dataArr = result;
});
})
Ben Nadel gives a nice explanation of this issue here.
Updated with HTTP and initial code based on requests/Please look at the bottom of the post:
I've been posting several questions on my AngularJS learning curve of late and the SO community has been fantastic. I've been a traditional C programmer when I used to program and have recently started writing my own ionic/Angular JS app. I'm struggling with the promise version of traditional async calls when it comes to converting a custom function to a promise. I don't think I really understood and I find various examples very contrived. I'd appreciate some help. I have some code which is not working, and I have some conceptual questions:
Let's take this simple function:
angular.module('zmApp.controllers').service('ZMDataModel', function() { return { getMonitors: function () { return monitors; } }
getMonitors is a simple function that basically returns an array of monitors. But here is the rub: When the app first starts, I call an http factory that does an http get and goes about populating this monitor list. This http factory is different from this service but invokes a setMonitor method in this service to populate the array. When the array is populated, a variable called 'monitorsLoaded' is set to 1. When this variable is set to 1, I know for sure monitors is loaded.
Now, I have a view with a controller called "MontageCtrl". I want to wait for the monitors to load before I show the view. In a previous post, one person suggested I use route resolve, but I had to first convert my getMonitors to a promise. So here is what I did:
angular.module('zmApp.controllers').service('ZMDataModel', function($q) {
getMonitors: function () {
var _deferred = $q.defer();
if (monitorsLoaded!=0)
{
console.log ("**** RETURNING MONITORS *****");
_deferred.resolve(monitors);
}
console.log ("*** RETURNING PROMISE ***");
return _deferred.promise;
},
Next up, in app.js I connected the route as follows:
.state('app.montage', {
data: {requireLogin:false},
resolve: {
message: function(ZMDataModel)
{
console.log ("Inside app.montage resolve");
return ZMDataModel.getMonitors();
}
},
Finally I modified my controller to grab the promise as such:
angular.module('zmApp.controllers').controller('zmApp.MontageCtrl', function($scope,$rootScope, ZMHttpFactory, ZMDataModel,message) {
//var monsize =3;
console.log ("********* Inside Montage Ctrl");
It seems based on logs, I never go inside Montage Ctrl. Route resolve seems to be waiting for ever, whereas my logs are showing that after a while, monitorLoaded is being set to 1.
I have several conceptual questions:
a) In function getMonitors, which I crafted as per examples, why do people return a _deferred.promise but only assign a _deferred.resolve? (i.e. why not return it too?). Does it automatically return?
b) I noticed that if I moved var _deferred definition to my service and out of its sub function, it did work, but the next view that had the same route dependency did not. I'm very confused.
c) Finally I ready somewhere that there is a distinction between a service and a factory when it comes to route resolve as a service is only instantiated once. I am also very confused as in some route resolve examples people use when, and I am using .state.
At this stage, I'm deep into my own confusion. Can someone help clarify? All I really want is for various views to wait till monitorsLoaded is 1. And I want to do it via route resolves and promises, so I get the hang of promises once and for all.
Added: Here is the HTTP factory code as well as the app.run code that calls this when the app first starts. FYI, the http factory works well - the problems started when I crafted ZMDataModel - I wanted this to be a central data repository for all controllers to use -- so they did not have to call HTTP Factory each time to access data, and I could control when HTTP factory needs to be called
angular.module('zmApp.controllers').factory('ZMHttpFactory', ['$http', '$rootScope','$ionicLoading', '$ionicPopup','$timeout','ZMDataModel',
function($http, $rootScope, $ionicLoading, $ionicPopup, $timeout,ZMDataModel) {
return {
getMonitors: function() {
var monitors = [];
var apiurl = ZMDataModel.getLogin().apiurl;
var myurl = apiurl+"/monitors.json";
return $http({
url: myurl,
method: 'get'
}) //http
.then(function(response) {
var data = response.data;
//console.log("****YAY" + JSON.stringify(data));
// $rootScope.$broadcast ('handleZoneMinderMonitorsUpdate',monitors);
$ionicLoading.hide();
ZMDataModel.setMonitors(data.monitors);
ZMDataModel.setMonitorsLoaded(1);
//monitors = data.monitors;
return ZMDataModel.getMonitors();
},
function (result)
{
console.log ("**** Error in HTTP");
$ionicLoading.hide();
ZMDataModel.setMonitorsLoaded(1);
//$ionicPopup.alert ({title: "Error", template:"Error retrieving Monitors. \nPlease check if your Settings are correct. "});
return ZMDataModel.getMonitors();
}
); //then
}, //getMonitors
And here is the code in app.run that first calls this:
.run(function($ionicPlatform, $ionicPopup, $rootScope, $state,ZMDataModel, ZMHttpFactory)
{
ZMDataModel.init();
var loginData = ZMDataModel.getLogin();
if ( loginData.username && loginData.password && loginData.url && loginData.apiurl)
{
console.log ("VALID CREDENTIALS. Grabbing Monitors");
// this calls http factory getMonitors that eventually populated the ZMDataModel
// monitors array and sets monitorsLoaded to 1
ZMHttpFactory.getMonitors();
}
}
I finally solved all the problems. There were various issues with my initial attempts. My final resolved solution is here Am I returning this promise correctly?
The learnings:
a) Separating the HTTP get into a factory and the data model into another service was unnecessarily complicating life. But that separation was not the problem. Infact, the way the promise was coded above, on first run, if monitorsLoaded was 0, it would simply return the deferred promise and there was no ".success" or similar construct for me to get into the resolve code block again.
b) The biggest thing that was making me run around in loops was deferring or rejecting was simply setting a state. the return always has to be the promise - and it would return the state you set. I assumed return d.promise always means returning "in progress".
(my case applies to C#, MVC, returning JSON, got jquery, angular), but I expect it applies to more than that.
I have a website where my angular/html/js calls ~7 services through Angular controllers and async-gets/displays data (weather, road conditions, etc). Some of these take longer than others (from ms to ~10s). I'd like to have a single call to my service which returns all of this data - but doesn't wait until the last call to return anything (10s).
Is there a way to make a single call, and return results as I have them and they get displayed accordingly? Do I need to have a repeating call which has a boolean like "IsMore=T" and calls the service again? (doesn't sound efficient).
Ideally, I'd like to keep a response channel open and keeping pumping results until it's done. Possible?
I'm not sure I understand completely, but I think you could just chain the response promises together, something like:
$scope.getWeatherData = function () {
return myWeatherService.get().then(function (resp) {
$scope.weatherData = resp;
});
}
$scope.getTrafficData = function () {
return myTrafficService.get().then(function (resp) {
$scope.trafficData = resp;
});
}
$scope.getWeatherData.then(getTrafficData).then(...chain others...);
This assumes that the service calls return a $http promise.
Anyway, whenever the promise comes in, the data will be on $scope, and hence the display will be updating as the promises arrive. It sounds like you might be using something like $q.all(), which would wait until all promises are resolved.
Buildilng on #reptilicus' answer:
$scope.getWeatherData = function () {
return myWeatherService.get().then(function (resp) {
$scope.weatherData = resp;
});
};
$scope.getTrafficData = function () {
return myTrafficService.get().then(function (resp) {
$scope.trafficData = resp;
});
};
$q.all([
$scope.getWeatherData(),
$scope.getTrafficData()
]).then(function () {
// do whatever's next, or nothing
});
... would request/receive both responses in parallel (if that's what you want). The relevant $scope property for each request will be populated when the related response is received, and the "do whatever's next" code will run once they are all complete.
Note, you need to inject $q to your controller constructor for this to work. :)
Edit: I just noticed that #reptilicus did mention $q.all. The difference between chaining the .thens and $q.all is that under chaining, one request wouldn't start until the previous was received....
what's the best way to declare a service I found this 2 different ways i can't seem to see the difference:
first method:
angular.module('app', [])
.factory('Data', ['$http',function($http){
return {
get: function(fileName,callback){
$http.get(fileName).
success(function(data, status) {
callback(data);
});
}
};
}]);
second method:
angular.module('app', [])
.factory('Data', ['$http', function($http){
var Url = "data.json";
var Data = $http.get(Url).then(function(response){
return response.data;
});
return Data;
}]);
Which one is better and why?
Thanks in advance.
There are a few things to separate out here.
Object vs Promise
Services are singletons, so in the second method (returning just the promise) your data will never be updated again. That's often the desired result. In your first method, it will be called fresh every time (though $http has a cache option).
From my perspective, one would only return a service object if there were multiple methods (e.g. get, create, delete, etc.) or it needed to be called multiple times. Otherwise, we're just piling on cruft.
Promise vs Callback
Promises are awesome - we should be leveraging them. Passing in a callback is nice, but it's also very limiting. With promises, we can easily chain them together, e.g.:
Data.get()
.then( massageDataFn )
.then( secondMassageFn )
.then(function ( data ) {
$scope.items = data;
});
Besides, $http already returns a promise. Why throw that away?
Method Parameters
Your former (object method) took in some parameters. While I am wary of a controller passing in an URL, there are some cases where it's desirable. But you can do this by just returning a function rather than an object:
.factory( 'Data', [ '$http', function ( $http ) {
return function ( fileName, callback ) {
// $http call here...
};
}]);
And then only the consideration is Object vs Promise, discussed above.
Conclusion
If your service has an API, return an object with public API methods, where each of those methods returns a promise. If your service is just to get some data once, just return the promise and be done with it.
The latter requires foreknowledge of the url and the callback function. The latter allows you to set both the target url and the callback, which is far more flexible. I would suggest going with the former in most cases, but it really depends on what you are trying to do.
The first sample makes the asynchrony of the HTTP request explicit for the service user, which is preferable, I think, to handing the service user a promise object (which is what "Data" is in the second sample) and letting the user proceed with its imperative operations, perhaps depending on a "Data" object that hasn't been filled in yet.
Your second method is a little more verbose, but one major benefit is the ability to create private properties / methods, and only return the public object.
Note that this should be planned around with regards to testing etc - from personal experience with Angular, private methods and properties are more difficult to unit test etc.
As an example:
angular.module('app', [])
.factory('Data', ['$http', function($http){
var private = {
property: 100,
method: function(data) {
return data * 2;
}
};
var public = {
property: true,
property_two: false,
method: function(data) {
return private.method(data + private.property);
}
};
return public;
}]);