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Angular Project Architecture

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.

Using backbone with multiple views and little models

I use backbone in most of my projects, and I think I know exactly what the M V C means: M for abstract of the data, V for representation and C for handlers.
However during my current project I found that there are a lot of views interactive with each other, while there are little modes(data with the server).
For example, I have there complex view named V1 V2 V3, when user do something in the V1, V2 should respond accordingly, so does the V3 and etc, and at the last step, a requst may be made to request data from the server. And most of the request are used to fetch data rather than modify data.
It does not like the common style: one(or more) view for one model such as the CRUD operation.
Now I have two ideas:
1 Virtual model
Create a backbone model to represent the state of the whole application, bind this model to all the views. Sounds like make the application as a state machine.
While it is not easy to describe the application with different states.
2 Use the event mediator
Use the event mediator to register/un-register different events, then the views can trigger or respond by different events.
While how to define the events to avoid insufficien or excessive, in a word to make the events orthogonal is not easy. Or I have not found any instructions yet.
Is there any other alternative solutions?

I think that it is a quite relevant question actually.
Create a backbone model to represent the state of the whole
application, bind this model to all the views. Sounds like make the
application as a state machine.
This doesn't seem like a very good idea, if the model isn't a consistent representation that corresponds to a specific backend resource.
Ideally, a view is a representation of a single model or collection. When a view would be bound to a model with unrelated properties, this doesn't seem too practical to manage in all circumstances, also due to an unforseeable future.
Use the event mediator to register/un-register different events, then
the views can trigger or respond by different events.
I don't think that it is overall a good idea to make views respond to custom events but this is personal for me. When apps become larger, assigning too much responsibility to complex views can become a mess; therefore I take it as a general rule to limit the task of the view to:
Rendering templates;
Activating plugins (if they're specific to the view);
DOM event binding;
(Model binding);
Methods internal to the view (related to the DOM);
Triggering custom events to notify other listeners when further action is required after interaction with the view;
In any case, in my experience I've found that it is practical to use a custom presenter/controller to instantiate / update views on custom events, and not let the view itself worry about these things at all. It keeps them clean and you always know what you will find there.
The views 1, 2 and 3 as you mention can be re-rendered from the presenters.
The presenter does something like:
"I get some data from a service and give it to some of my views that require
them. If something changes, I'll let them know"
I usually have 1 presenter per related set of views.
I like this approach because:
It keeps logic for related views centralised;
When an event is triggered, the presenter needs to listen only once for all the views that it controls;
Presenters are given the authority to talk to each other, which is to my feeling easier to control than when all views would start talking to each other through each other;
In simple cases, all of this doesn't matter too much probably. But when building a larger application, I found that it can become a mess.
My two cents

I have there complex view named V1 V2 V3, when user do something in the V1, V2 should respond accordingly, so does the V3 and etc
It doesn't seem like you have 3 views, but in fact 1 view with 3 interrelated sections. I would use one super view that renders 3 child views, and listen to view events. For example:
Backbone.View.extend({
initialize: function () {
this.v1 = ...;
this.v2 = ...;
this.v3 = ...;
this.v1.on('user do something', this.v2.respondAccordingly);
this.v1.on('user do something', this.v3.soDoesEtc);
}
})
And in view 1:
$('button').on('click', function () {
self.trigger('user do something');
})

This is a problem that many Backbone developers face.
What I've done in the past is to have a baseModel/baseCollection, and treat them as an abstract class/interface from which other models/collections extend, respectfully. These base objects would contain a listener/trigger methods which I could then use across my application to have changes in one model/collection be able to initiate updates on collections/models (thus triggering view changes) respectively as I chose. Using this method allowed me to compose my application by having the appropriate objects listen/broadcast events appropriately as I wished.
One of my friends created a server-side JS state machine which would initiate super-models (app-level model which in turn could trigger sub-view model/collection updates).
Of course, Marionette provides a framework that makes this a little less manual and allows you to get back to writing app-code.
One of the joys and burdens of Backbone.js is that you have all the flexibility you want. :)

Backbone Design - Multiple Views, Same Model, separation of events

I am quite experienced with JS and Backbone, but want your help brainstorming a best practise solution to the following problem:
There are two views. They sit side-by-side running concurrently in the page.
Both of these views are passed the same instance of a model.
Both of these views have actions which can update the model.
How, using Backbone's event driven programming, do you think would be the best way of distinguishing the events fired from view to view.
A possible scenario could be:
The user performs an action which updates the model in an invalid way on View A. But as the user did not perform it on View B they should not be notified there.

You can use intermediary objects to manage the flow between a repository (the object where the connection to the database takes place) and the instantiation / manipulation of views.
Instead of binding a model to a view from within the view, you can let the intermediary object (general purpose controller) make verifications, if required manipulations, before re-rendering the view with the modified model or collection.
Through the use of an event aggregator, you can trigger events from views from within the view, and listen to the event from within the "controller" object, who will in turn perform the required custom actions.

Using custom events seems simple enough. Just treat each view's actions as if they were different and name the events differently for each view (example this.trigger('view1:event1'), this.trigger('view2:event2')).
Make sure the views are subscribed to these specific custom events to avoid collisions on actions that would trigger events on both views (like attribute updates).

Backbone.js shared context model

We have a backbone.js application that needs to have a shared context model storing the environmental variables of the application, which can trigger events in multiple views. An easy way to do is to use the same model across multiple views, serving like a global object. But I have two issues with this design: first, it seems to be a bad design pattern using a global variable; second, it forces all views to use the same model, which created the undesirable strong coupling between views even though each view can be set to listen a subset of the model attributes.
One solution that I am considering is that a child view can have his own model with this shared context model as one of its attributes.
I am new to backbone.js, so I am wondering what other alternative solutions people are using.

Take a look at backbone.wreqr, which contains a global event aggregator and is a part of the great Backbone.Marionette library.
Then you can share the event aggregator instance between the views and have them listen to events triggered from the environmental variables module.

Backbone relationship between the view and the router

I believe that in the data-driven programming paradigm, the router and the view should be isolated from each other, and they communicate to each other only through model changes, which they both subscribe to.
However, the various tutorials online all do this differently. I have seen code that instantiates a view inside the router's initialize method, and hence giving the router a way to access the view. I have also seen code that passes the router to the view, so that the view can listen on the changes on the router's route events.
I don't believe either approach is right, as it breaks the separation of concern. As I am new to Backbone, can someone more experienced and knowledgable confirm?

I don't see any problem using the Router to instantiate Views, actually is the way I use to work. The Router detects a new URL and detach any not used View and instantiate the requested ones.
Passing the Router reference to the View can be uglier, not to say too much effort to keep the reference traveling between Views and SubViews.
But in the other hand Views have to be able to send signals to the Router to change the navigation so I also go for the easy way and make the Router globally visible for all elements in my App and I can call App.router.navigate() from any View without having to remember to pass the reference explicitly. This decision can be defended because only one Router instance is allowed in any Backbone application.

In some projects I have used a global event dispatcher, which passes the routing events to the views.
window.Dispatcher = _.extend({}, Backbone.Events);
In the router you can bind to 'all' event which captures route:* events:
initialize: function() {
this.bind('all', this.onRoute);
},
onRoute: function(route) {
Dispatcher.trigger(route);
}
In your views you can bind to Dispatcher events and react to route changes:
initialize: function() {
Dispatcher.on('route:index', this.onIndex, this)
}
This is similar to having a model that changes when the route changes, but I feel this is easier to manage, and also doesn't require passing the router to views. Not sure if this is the right way to do it, but then again Backbone enables you to do things in many different ways.