service as a collection and a controller's access to it

[Jonathan Price]

I've got a service that has a collection of things.  It also has an individual thing of the same type.  I'll use a service like this to pass around between controllers when I have a collection of things that I'll individually want to update.    Imaging a collection of say books.  I can display the collection through a table, click on one to edit, update it and reload the entire collection..

I've got a plunker here that shows what I'm confused by:

http://plnkr.co/edit/P2smRGGAjEIHbZyAAKKR?p=preview

I don't understand why my controller's scope isn't staying directly tied to the service values?  I thought they became associated by reference when I set them equal to one another in my controller? 

Thanks!

[Tony pee]

The problem is with your understanding of how references work in javascript i feel. In a small example:

var obj = { prop: 123 }; an object with a property

var ref = obj.prop;

ref = 456; // this will NOT mean that  obj.prop == 456, it means that ref is equal to a primitive value of 456. obj.prop is untouched. 

In your example, when you do lines like this: 

$scope.model.allModel = MainSvc.getModel(); 

you set on $scope.model (a different object) a reference to the object which is ALSO stored in your model class. when you change the value of $scope.model you just change what that reference is pointing to. The object referenced in your service is untouched. You should try directly referencing the value stored on the model. And you dont really want to set it on the controller, otherwise you'd need to also update it on the service to make it share between controllers (original purpose). So its better to prove that it can be shared:

http://plnkr.co/edit/Q054Lw0Mi80LRnCBKlg6?p=preview

I changed the style to a more class like style. And kept your getters and setters, altho they arent really needed (see the direct method works too)

 

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Tony Polinelli

[Tony pee]

This is a more minimal example, how id name things (no pun): 

http://plnkr.co/edit/qpWKOh4zSMtTGgjmWYV0?p=preview

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Tony Polinelli

[Tony pee]

or if you want to wrap the service in methods at the controller level (often a good idea)

http://plnkr.co/edit/2OxsdgZYozIIutVGEqYf?p=preview

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Tony Polinelli

[Puritan Paul]

Right, I see what you mean.  I definitely thought that type of assignment was by reference.

Can you tell me then why when I push or pop a new element to the services, my controller reference is updated accordingly?  Are arrays passed by reference and objects not?

As I typed that I realized I could easily search and find out myself…

Thanks for the help!

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[Tony pee]

when you assign an object (not a primitive) to a variable (or a property of another object) then you are assigning a reference to the object. The variable only stores the reference to the object. The object is stored in memory, and can be referenced by many variables, as im sure you know. If you use methods on the referenced object then you will mutate it (possibly - depending on the method). So, in the case of using push/pop on an array, they mutate the array, by adding/removing items. 

This is the same for any instance of object (instance of class if you want to think classically), that you create. You can mutate it however you want, you can assign new properties/methods (objects are dynamic), or mutate it in any way you want. aslong as you are working ON the reference. 

eg:

var obj = {};

obj.one = 1; // mutating obj

obj.test = function() {} // mutating obj

var obj2 = obj; // another reference to the 'obj' object

obj = {} // creating a new empty object and assigning a reference to it under the variable 'obj' 

obj2.one // still exists and == 1, as the object created initially still exists and is referenced by the obj2 variable. 

obj2 = 2 // reassigning the variable obj2 to a primitive value of '2'

// now there are no references to the object that was previously assigned to obj1 and obj2, therefore it will be cleaned up by garbage collection (removed from memory) 

hope that helps