How would you implement something like this in Angular:
I have a multi-page user interaction that shares state across pages/controllers. Page A launches a multi-page process across pages B, C, and D. I need to share state across pages B-C-D but as soon as the user goes back to page A (either at completion, or abandoning halfway through) the shared B-C-D state should go away.
I could put the shared state in a service and that would take care of sharing across pages. But then it's a global singleton for the whole application. Is there a way to ensure the service is disposed if the transaction is abandoned or completed?
In the server-side, Java EE world this was called "conversation scope" - I'm wondering what the equivalent might be in Knockout or Angular.
Or there a better way to approach the design? Should I use nested controllers?
This is a pretty broad question and is going to certainly elicit some opinion based responses. That said, one of the things you can rely on is that services (and factories) are singletons. What that means is if you need to share data between controllers, or across the life of a SPA you can create a service to hold and share that data. That service and its data will exist as long as the page isn't re-loaded.
The basic pattern for a shared data factory is like this is:
// define the shared data service
app.factory("SharedData", function () {
return {
// just one data object for the purposes of the example
sharedDataObject: {}
};
});
Once you have defined the service you can define a controller that uses the service something like:
app.controller("FirstController", function ($scope, SharedData) {
$scope.localData = SharedData.sharedDataObject;
});
Because we have defined the shared data as an object and not as a value - binding to "localData" will allow us to set values that can then be retrieved for as long as the page isn't changed. I put together an example that shows sharing data between two controllers here. This pattern works just as well if the controllers were on separate views.
Again - I'm not sure if this is the recommended pattern but it is one I have seen around and it works pretty well. Best of luck!
NOTE - This answer is referenced in your question - so it probably isn't exactly what you are looking for. That said, I am posting for others that may need a simple method of saving state on an SPA.
If you put the shared state into a service, just add a reset() function to it that gets called when they go to the "A" step or when they complete the process.
And I think you could do it with a nested controller too. You'd probably still need to add a reset() function for handling all the cases.
Related
We have developed one Enterprise application, The complete client side framework is built on AngularJS and the server side framework is on ASP.NET Web API. In the application we have 350+ html pages and 250+ Web APIs. There are lots of areas where we initialize the server data from ng-init directive via calling controller function. Because in our application all data is coming from the ASP.NET Web APIs. But I was surpised upon the documentation for ng-init, which says, in a nice bold outline :
The only appropriate use of ngInit for aliasing special properties of ngRepeat, as seen in the demo below. Besides this case, you should use controllers rather than ngInit to initialize values on a scope.
I would like to get feedback from Industry Experts/ Angularjs Core Team Members on my concerns.
Let me brief first what we are doing in the application, for showing a industries list we load the industry HTML page and show the server data. The HTML template code is shown below:
<div ng-init="initIndustries()">....</div>
The "initIndustries" function will be called from initialized industryCtrl. industryCtrl.js code is shown below :
app.controller("industryCtrl",["$scope",function($scope){
//Sets the server data in the $scope property.
$scope.initIndustries = function(){
//perform ajax request and set the data into the $scope property.
}
$scope.initAddIndustry = function(){
// perform ajax request for getting a dropdown data on Add Industry Page.
}
}])
I have few concerns based on Angularjs Doc and Anglarjs-styleguide guideline on Keep Controller Focused which is mentioned below :
Are we doing something wrong to initialize the data via function because all data is coming from the Server APIs?
Current initialization approach is against the industry practices in AngularJS based application. if yes, then which approach we need to follow in the application?
Do we need to create sperate controller for every view just for the shake of client side test coverage, as per the angularjs-styleguide?
The reason to implement the above approach(initialize the data from ng-init directive via controller function), Due to large application my initial thought was to follow MVC philosophy of decoupling the code and separation of concerns.
Angular is known to be Model-View-Whatever. So, it totally depends on you whether you follow a structure in the angular application or not.
Not following a structure has some pros and cons.
Pros
1. A data that is available in one controller can be shared across many views so you won't have to use $rootScope or HTML5 localStorage/sessionStorage to pass data from one controller to another.
Cons
1. As data in controllers is available in multiple views so it is very difficult to maintain the data because the data is obviously bound to views and there will be many implicit angular watches on the same data. That will give bad performance.
Now answering your point 1 and 2 of using ng-init to intialize data in controller. I don't think that will be a good approach because you have made the initialization dependent on the view.
Lets take a scenario in which your view is not found on request and then the initialization won't occur. And as initialization won't occur, there will be garbage values / bugs in controller. So its better to separate the controller initialization from view.
Answer to point 3 is that when you are using a separate controller for every view, you are actually avoiding monolithic code approach and that is always a good point because that leads to modular approach. Separation of concerns in Angular JS is not just done using separate controller for every view but services and directives are also for this purpose in the long run.
Hope that helps you in some way.
I am building an app in angular, which consumes different APIs and Gives options for the user to select it will be recorded and sent back to the server.
I have designed it as follows.
All the common logic in Main Controller and all other options in different controllers as the child of main controller.
Main Controller retrieve all the data that are required to run the app.
which is consumed by all other child controllers.
To make sure data is loaded I am using promise attached to scope. So all the child controller will know data loaded.
I have moved data updation part of all child controllers to main controller
because all the updates happen in one object.
Child Controller emit/broadcast to communicate between child and main. So when update happens child will emit an event with data which will be captured by Main and it will do the update.
MainController {
$scope.loaded = DataService.get();
$scope.userOptions = {};
$scope.$on('update',function(){
updateUserOptions();
})
}
ChildController {
$scope.loaded.then(function(){
//all logic of child controller
}
$scope.onselect = function(){
$scope.$emit('update',data);
}
}
Questions
Is it a good practice to use events between controllers ?
is it good to use promise attached to scope for child controllers ?
Will it improve my code if I start using services ?
I will try to answer your question based on my own experience. Recently I've built a single page application and I've refactored its architecture.
Here are my answers:
Is it a good practice to use events between controllers? IMHO, it is the most flexible way to share information between all controllers even if they have isolated scope (using $broadcast or $emit for example). This is called the Observer design pattern. However, you can use services instead of events to share data between them. If you are going to use $rootScope, be careful as all the $scopes inherit from $rootScope.
is it good to use promise attached to scope for child controllers ? Firstly, you have to learn about how scope inheritance works. You have to take care to avoid property shadow in JS. Secondly, I would move out all the logic from scope.loaded in ChildController to a service such as ChildService. Keeping the business logic (such as request, etc) in Services instead of Controllers, will ensure it can be re-used.
Segregation of business logic is good design principle.
Will it improve my code if I start using services ? I answered this question above.
In addition, in order to build a good architecture I've read this angular style guide written by John Papa.
I recommend the following changes:
To make sure data is loaded I am using promise attached to scope. So all the child controller will know data loaded.. Instead I would emit a custom 'loaded' event in the MainController using $scope.$emit('loaded'). After that, in the ChildController I would use $scope.$on('loaded', function(){}) to handle the event.
I would move the updateUserOptions function to a service and inject the it into just the controllers that need it.
I hope that helps!
Is it a good practice to use events between controllers ? Not as the main form of data sharing, but you can use it to notify about system events, such as data ready.
Is it good to use promise attached to scope for child controllers ? Don't use scope inheritance, it causes lots of annoying problems.
Will it improve my code if I start using services ? Yep.
This is what I would do in your place:
dataService - this service is responsible for all data coming in / going out. Whenever a request for data is made (no matter which controller asked for the data), the service caches the data (save the promise is good enough). All further requests get the cached data unless they specify they want a fresh data. Whenever data is updated (1st time or refresh), the service broadcasts a 'dataReady' event via $rootScope to which the main controller and other subscribers can listen.
The service is also responsible for data updates, and when the data is updated you can also broadcast an event via the $rootScope.
When the event is activated, all subscribers query the service, and get the data they need.
Controllers - avoid controllers, use directives with isolated scope, and pass the data between them using attributes. In this way you can be sure that each directive gets what it needs, and not everything. The directives can communicate using attributes, services, broadcast / emit or require their parents / siblings if they work closely together.
Is it a good practice to use events between controllers ?
No it's not, it will be deprecated by Angular JS 2.0. It also often leads to unmanagable tangle of events which are hard to understand and debug. Use services to share data between controllers. (Inject same service into multiple controllers, service then holds data, controllers bind to that data and are automatically synchronized) I wrote a blog post explaining this use case.
Is it good to use promise attached to scope for child controllers ?
No it's not. Use promises and resolve data in services. Don't use $scope at all but use controllerAs syntax instead. $scope was deprecated also in Angular JS 1.X because it's usage leads to many different problems with scope inheritance.
Will it improve my code if I start using services ?
YES! Use services for all logic and data manipulation. Use controllers only for UI interaction and delegate everything to services. Also use ui-router for managing state of your application.
I'm not going to answer your questions directly as I have some other comments as well. I think the approach you mentioned is not the best way to build angular applications.
All the common logic in Main Controller and all other options in different controllers as the child of main controller.
It's against all angular style guides to place common logic in controllers. Controllers should only be used for the logic related to the view (data binding, validation, ...). Because the code inside a controller is not reusable, the less code you have in a controller the better. The more logic you have in services, the more scalable your application becomes.
Fix: I suggest you create a service that retrieves data from the server, and inject this service in controllers as you need. Notice also this way offers better dependency management as you can keep track of which controllers need which services exactly.
Nested controllers should be avoided when possible, because angular keeps track of all the active scopes and re-evaluates them in every $apply() loop.
Fix: same as #1, use services instead of the main controller.
To make sure data is loaded I am using promise attached to scope. So all the child controller will know data loaded.
Using a promise for data retrieval is a good practice. But, again, keeping it in a service is much cleaner than main controller.
I have moved data updation part of all child controllers to main controller because all the updates happen in one object.
Child Controller emit/broadcast to communicate between child and main. So when update happens child will emit an event with data which will be captured by Main and it will do the update.
Fix: use a service with an update function instead of events. Events are harder to debug and track. And you need to unregister event handlers on destroying a controller. If you can use a function/promise instead of events, then it's usually a better idea.
Is it a good practice to use events between controllers ?
A problem with your current set-up is that you're implicitly relying on the hierarchy of your controllers (the fact that one is the child of the other) - because you emit the event, only scopes higher up on the hierarchy can catch it. Besides being an implicit connection (that a developer has to remember), this also limits he extendability of this feature.
On the other hand, if you injected a shared service into all the controllers that need it, the connection between the controllers would become explicit and documented, and their scopes' position in the hierarchy independent. This will make your architecture easier to maintain, with the added benefit of also being easier to test, for one.
You can still implement an observer pattern with a service.
is it good to use promise attached to scope for child controllers ?
The issue of polluting scopes pointed out in other answers is valid. This is one of the reasons why it's better to limit the number of objects you attach to your scope, and to use objects as bundles of variables on your scope instead of attaching all the variables to the scope directly.
(For an explanation of these reasons, see discussions about "always having a . in your bindings".)
(Of course, don't do this blindly just to reduce the number of variables, try to find semantic connections between variables that might be bundled together sensefully.)
Will it improve my code if I start using services ?
I think the above answers already outline the answer for this: yes. There are other benefits too, but this format is not best for too long answers, so I won't list anything else now.
All in all, these above pointers are not big issues with your code currently, but if you're looking for the best architecture, I think you can do better.
Answers:
No, it will be deprecated soon.
$scope is deprecated already.
Services is a great choice. Services allow us to share data and behaviour across other objects like controllers.
I'm trying to grasp the main principles related to the next issues:
Templates
Data Handling
$resource vs $http
As i see it i'd like to implement few views in my app which share few html templates and also share some data. for simplifying my issue i'll describe a scenario which is almost equivalent.
as u can see there are 2 views (though there will be more!) who use 3 html markups while one of them is shared in both views (GeneralInfo). Also, both views share data which will be normally created while using one of the view's controller.
What principle of angular should be used to make sure that while changing the route i could keep my data shared between the views.
Should i use app.value('myVal', ..) which is Global variable?
Should i pass it like a service to all of my controllers?
More technically, how should i implement same html in both views? could u example that?
How should a view with it's markup contain 2 templates and how and when it is rendered?
what's the difference between $resource and $http and when each shouold be used?
1) should use a Service to share data between controllers. technically, you could attach values on $rootScope and it would be visible across controllers, but that is considered bad form and can cause problems later (like using global variables -- can definitely have unintended side effects as the project grows if someone accidentally attaches a conflicting value).
2) not sure exactly what you're asking here. you can load a partial based on the given route/state (using ngRoute or ui-router). two different routes could use the same generalInfo.html partial, but with different data being pulled in their respective controllers. is that what you're asking?
3) $resource is an abstraction of $http -- if you're pulling data from a REST server, $resource may be a better fit, as it abstracts a little of the wiring necessary. however, if the server varies from traditional REST principles too much, or if it's not REST at all, you may just want to roll your own data access directly with $http. Of course, if it's REST and more complex, also consider restangular -- which is a more feature rich abstraction.
I'm learning angular, experimenting with different ways of using services/factories, and am trying to wrap my head around the unique sense in which they are "singletons".
I have an API service that exposes domain models and wraps functionality for retrieving them from my REST server. This service can be easily comprehended as a singleton in the classic sense: I want a single instance to be shared across my application, with a state that can be observed by many different controllers, enabling those controllers to "synchronize" with each other through the conduit of the service: The controllers stay in sync not by being aware of (and thus coupled with) each other directly, but by being aware of this common service. (side question: is this a correct characterization of the role of a service?)
This is a use-case where a singleton service is clearly and unambiguously appropriate. But:
One of the domain objects that gets returned by the API service is called thread, which is essentially a wrapper around a linked-list of points. In addition to the list of points, a thread has a currentPoint variable and a next() function, which pops the next value from the list and makes it the currentPoint.
My UI visualizes a thread simultaneously in two different ways - in two separate elements with their own controllers and directives. Each of these elements contains a button that, when clicked, calls nextPoint() and thereby changes the state of the thread. When this button is pushed in one element, the state of the thread needs to be updated in both elements - so, here again we have a situation where a service seems ideal.
But, at any given time, there can be an arbitrary number of threads being displayed, each of which should be independent and unaware of each other - which conflicts with (what I understand to be) the "classic" sense of "singleton".
Is there a word for this sort of thing in angular?
I've experimented/looked into this enough to know that it's certainly possible to create these "non-singleton singletons" using factorys, but surely there must be a better term for them than "non-singleton singletons" - I cringed both times I just typed it.
Second, what is the best way of implementing one? Can the strategy illustrated below (which I found in an angular github issue here) be regarded as a best practice?
myApp.factory('myServiceProvider',function(){
var serviceProvider=function(){};
serviceProvider.prototype.foo=function(){};
var service = {
getInstance:function(){ return new serviceProvider(); }
}
return service;
});
//Singleton Services
myApp.factory('myService',['myServiceProvider',function(myServiceProvider){
return myServiceProvider.getInstance();
}]);
//Where non-singletons are required
function myController(myServiceProvider){
var instance_a=myServiceProvider.getInstance();
var instance_b=myServiceProvider.getInstance();
};
//Where singleton service is required
function myOtherController(myService){
myService.foo();
};
An angular singleton is not exactly the classic. A singleton in angular is basically one instance of an object that holds a single state. That state can be data bindable via a services allowing for value sharing. This means that you can have a service property that is bound across all of its uses an app; one change will be reflected everywhere. The singleton persists through the life of the app. If the app is refreshed the singleton will loose value until it is set again by the app via a user interaction or a storage retrieval.
I like the pattern you are using. I also tend to use it. Here is an example of a web storage service I recently made similar to your service, https://github.com/breck421/WebStorage/blob/master/src/js/WebStorage.js.
I hope this helps and feel free to continue this dialog :)
Thanks,
Jordan
What is the difference between implementing a $rootScope function and a service? Security wise or performance wise.
I have read this, so I am wondering.
I have been trying to figure out whether or not a certain global function for my app would be best implemented in a service or on the $rootScope itself. To pitch you guys with an idea of what I am making, I'm currently developing a dirty form function in which it prompts the user if he/she navigates away from a certain form. In this case, I decided to best implement it as a global function, so any hints?
Thanks for the responses,
Jan
In this case I would go for a service to avoid having a global state. all new scopes are created from $rootScope. New controllers or whoever uses a scope will have values of $rootscope available. For instance, if you define $rootScope.validate() and in a controller you define a function $scope.validate() because you forget about the first definition, something will certainly go wrong.
There is an article by Misko H. about this http://misko.hevery.com/code-reviewers-guide/flaw-brittle-global-state-singletons/
Services are instantianted on demand, whereas $rootScope is created during bootstrap, and can be injected wherever you need them. This is good for testability.
Angular won't instantiate services unless they are requested directly or indirectly by the application.
(http://docs.angularjs.org/guide/dev_guide.services.creating_services)
As #egamonal mentioned Services are more robust way to share common functionality. Not only services are instantiated on demand, they are singleton by nature so once a service gets created, the same instance gets passed around by AngularJS whenever requested. So if something can go on root scope, it can also be implemented using a service.
One think to keep in mind using such global approach is the possibility on memory leak. Instance of JS classes or maybe DOM elements remain in the memory because you have referenced them from you global functions (either in $rootscope or service).