According to this article: http://www.maltblue.com/tutorial/zend-framework-2-servicemanager
The ServiceManager is "in short a simple application registry that provides objects". So, I would think that it should be a singleton that we can have access anywhere in the application. But in case of ServiceManager, it isn't.
Why can't I get the service locator instance anywhere in the application?
ServiceManager basically act as container. Inside the container you satisfy various dependencies of an object you create and then return it to be used by other objects.
So in a way SM sits over the object, not goes inside the object. If you are using SM instance inside the object (probably to access other services) then you are going against the principle of Inversion of Control.
Following are the two ways
class A {
private $data;
public function __constructor($sm) {
$this->data = $sm->get('user_data'); // Service manager accessed inside the object
}
}
Other way
class B {
private $data;
public function __constructor($user_data) {
$this->data = $user_data; //$user_data getting injected from sm container
}
}
Somewhere inside Module.php:
'factories'=>
array(
'objB'=> function($sm) {
//this is the container where sm sites outside the object to satisfy its dependencies
$objB = new B($sm->get('user_data'));
return $objB;
}
)
In second example dependency ($user_data) gets injected into the object.
Here is a simple way to get ServiceLocator to instantiate objects wherever you want...is a very simple module that set ServiceLocator on application's bootstrap to a static variable in a class...you can get an idea to create something more sophisticated if it doesn't fit your needs :) Here is the module... https://github.com/fezfez/ServiceLocatorFactory
Related
I have been using Proto.Actor and specifically the ActorFactory to spawn actors. To be able to use these features I need to add services.AddProtoActor() to the ConfigureServices method of my startup class.
However, now I want to transition to using StructureMap as my IoC container, but the two do not appear to play nicely together - when I add the following code from guides I have found online:
public IServiceProvider ConfigureIoC(IServiceCollection services)
{
// static class method that scans assemblies
IContainer container = IocContainer.SetupContainer();
container.Configure(config =>
{
config.Populate(services);
});
return container.GetInstance<IServiceProvider>();
}
When it tries to run config.Populate I get the following error:
System.ArgumentOutOfRangeException: Specified argument was out of the
range of valid values. Parameter name: EventStream must have at
least one public constructor to be plugged in by StructureMap
Does anyone have any ideas how to get the IActorFactory created correctly as a singleton in StructureMap (or have a workaround)?
In the end, using StructureMap removes the need I had for the ActorFactory itself. So instead of getting the actor's PID from the factory I have two lines:
var props = Actor.FromProducer(() => container.GetInstance<MyActorType>());
var pid = Actor.Spawn(props);
In my controller, via service, I get from DB a list of the names of widgets (eg. chart, calendar, etc). Every widget implements WidgetInterface and may need other services as its own dependencies. The list of widgets can be different for each user, so I don't know which widgets / dependencies I will need in my controller. Generally, I put dependencies via DI, using factories, but in this case I don't know dependencies at the time of controller initialization.
I want to avoid using service locator directly in controller. How can I manage that issue? Should I get a list of the names of widgets in controller factory? And depending on widgets list get all dependencies and put them to controller?
Thanks, Tom
Solution
I solved my issue in a way that suggested Kwido and Sven Buis, it means, I built my own Plugin Manager.
Advantages: I do not need use service locator directly in controller and I have clear and extensible way to get different kinds of widgets.
Thank you.
Create your own Manager, like some sort of ServiceManager, for your widgets.
class WidgetManager extends AbstractPluginManager
Take a look at: Samsonik tutorial - pluginManager. So this way you can inject the WidgetManager and only retrieve the widgets from this manager as your function: validatePlugin, checks whether or not the fetched instance is using the WidgetInterface. Keep in mind that you can still call the parent ServiceManager.
Or keep it simple and build a plugin for your controller that maps your widget names to the service. This plugin can then use the serviceLocator/Manager to retrieve your widget(s), whether they're created by factories or invokableFactories. So you dont inject all the widget directly but only fetch them when they're requested. Something realy simplistic:
protected $map = [
// Widget name within the plugin => Name or class to call from the serviceManager
'Charts' => Widget\Charts::class,
];
public function load($name)
{
if (array_key_exists($name, $this->map)) {
return $this->getServiceManager()->get($this->map[$name]);
}
return null;
}
Injecting all the Widgets might be bad for your performance so you might consider something else, as when the list of your widgets grow so will the time to handle your request.
Hope this helped you and pushed you in some direction.
This indeed is a interesting question. You could consider using Plugins for the widgets, which can be loaded on the fly.
Depency injection is a good practise, but sometimes, with dynamic content, impossible to implement.
Another way to do this, is to make your own widget-manager. This manager then can load the specific widgets you need. The widget-manager can be injected into the controller.
Edit:
As you can see above, same idea from #kwido.
I would use a separate service and inject that into the controller.
interface UserWidgetServiceInterface
{
public function __construct(array $widgets);
public function getWidget($name);
}
The controller factory
class MyControllerFactory
{
public function __invoke(ControllerManager $controllerManager, $name, $requestedName)
{
$serviceLocator = $controllerManager->getServiceLocator();
$userWidgetService = $serviceLocator->get('UserWidgetService');
return new MyController($userWidgetService);
}
}
Then the logic to load the widgets would be moved to the UserWidgetServiceFactory.
public function UserWidgetServiceFactory
{
public function __invoke(ServiceManager $serviceLocator, $name, $requestedName)
{
$userId = 123; // Load from somewhere e.g session, auth service.
$widgetNames = $this->getWidgetNames($serviceLocator, $userId);
$widgets = $this->loadWidgets($serviceManager, $widgetNames);
return new UserWidgetService($widgets);
}
public function getWidgetNames(ServiceManager $sm, $userId)
{
return ['foo','bar'];
}
public function loadWidgets(serviceManager $sm, array $widgets)
{
$w = [];
foreach($widgets as $widgetName) {
$w[$widgetName] = $sm->get($widgetName);
}
return $w;
}
}
The call to loadWidgets() would eager load all the widgets; should you wish to optimise this you could register your widgets as LazyServices
I am trying to find out how I can pass the StructrueMap container to a class that I wrote that inherits from another (MS-Class).
namespace TheNamespace
{
public class DatabaseIssuerNameRegistry : ValidatingIssuerNameRegistry
{
/* **This can't be done**
public DatabaseIssuerNameRegistry(IPortalTenantManager portalTenantManager)
{
_someField= portalTenantManager;
}*/
protected override bool IsThumbprintValid(string thumbprint, string issuer)
{
//How does it work ???????????
var portalTenantManager = container.GetInstance<IPortalTenantManager>();
//Do something with the portalTenantManager
}
}
I need portalTenantManager to be the Instance that I have defined in my container in the Global.asax.
My Global Assax has these things setup:
protected void Application_Start()
{
var container = new Container();
container.Configure(x =>
{ ....
....
x.For<IPortalTenantManager>().Use<PortalTenantManager>();
});
...
...
ControllerBuilder.Current.SetControllerFactory(new StructureMapControllerFactory(container));
...
GlobalConfiguration.Configuration.DependencyResolver = new StructureMapApiControllerFactory(container);
...
}
Edit:
Because of the comments of #NightOwl888 I'll explain a bit further what this class does. (Hopefully explaining so why my hands are tied)
My application is able to authenticate a user with Azure Active Directory and is Multi-tenant capable. In the authentication pipeline I have the possibility to store the validation endpoints in my database instead of the default way on the web.config file. See MSDN
and this, which actually is explaining exactly what I'm doing.
So I registered my class in the web.config under the Tag issuerNameRegistry. At some point of the validation pipeline my class is instantiated and the overriden method IsThumbprintValid is beeing called. The problem is that the class registered in issuerNameRegistry expects a parameterless constructor (there it is! the constrained construction!), therefore I cannot create a constructor that would solve my problem.
Thanks for your help
It turns out that this question has been asked before on MSDN, the answer of which was provided by Travis Spencer in 2 different posts.
it is typical in my experience to have a single container and use that service- or Web-side-wide. In the startup of the service or Web app, you can create the container, register the dependencies, new up an instance of your SecurityTokenServiceConfiguration class, resolve your dependencies, use it to punch out a SecurityTokenService object, and host it.
After the first beta, we really pushed for DI support. We got a little hook in beta 2. You can now create a custom SecurityTokenServiceConfiguration class that overrides the virtual CreateSecurityTokenService method. The implementation in Microsoft's SecurityTokenServiceConfiguration does Activator.CreateInstance; yours can do IoC. This can include the resolution of an IssuerNameRegistiry. Something like this perhaps:
RequestSecurityTokenResponse Issue(IClaimsPrincipal principal, RequestSecurityToken request)
{
SecurityTokenServiceConfiguration config = new MyGoodSecurityTokenServiceConfiguration();
SecurityTokenService sts = config.CreateSecurityTokenService();
RequestSecurityTokenResponse rstr = sts.Issue(principal, request);
return rstr;
}
public class MyGoodSecurityTokenServiceConfiguration : SecurityTokenServiceConfiguration
{
public override SecurityTokenService CreateSecurityTokenService()
{
IssuerNameRegistry = IoC.Resolve<IssuerNameRegistry>();
var sts = IoC.Reslove<SecurityTokenService>();
return sts;
}
}
Of course, this means that you need to create a static instance of your DI container so it is accessible to your SecurityTokenServiceConfiguration class. Personally, I don't like that idea because it makes your DI container accessible throughout the application, which can lead to abuse of the DI container as a service locator.
Ideally, there would be a way in any DI friendly framework to pass the container into an abstract factory in order to resolve service dependencies. However, since I am not familiar with WIF it is unclear whether that can be done - perhaps the class where the Issue method exists could have a constructor added? The trick is to keep walking up the chain until you find the first place in the framework where you can intervene and do all of your DI configuration there.
How can I create a Singleton instance in di.dart?
Seems like if I do this:
module = new Module()
..bind(GameRepository)
..bind(MessageFactory)
..bind(Broadcaster);
my GameRepository gets instantiated multiple times if when I do
injector.get(GameRepository)
I tried to do
..bind(GameRepository, toValue: new GameRepository())
and that seems to work, but it's easy because GameRepository has no parameter, but shouldn't there be a way to tell the di framework to bind it as a singleton without requiring me to instantiate it (and maintain its constructor call?)
edit:
#Günter, I do want a Singleton, however in my case I want to use my GameRepository from my redstone.dart resource AND from outside too. So I bind the GameRepository and then do this:
// To use it outside of the resource
injector = new ModuleInjector([modules.getProductionModule()]);
// To use it in redstone
app.addModule(module);
And now I can see that redstone hold a different reference on GameRepository from the one I get when I do injector.get(GameRepository)
I don't know if the question has become too specific though :P
As far as I know DI always returns the same instance, therefore everything is a singleton. If you don't want singletons you can bind a factory.
For more details see https://stackoverflow.com/a/22944185/217408
How about using a factory constructor with the singleton pattern in an implementation or extension of that class
class GameRepositorySingleton extends GameRepository{
static GameRepository _instance;
factory GameRepositorySingleton (A a, B b, ...){
if (_instance == null)
{
_instance = new GameRepository (a, b);
}
return _instance;
}
}
and then you can use it in DI like this
module = new Module()
..bind(GameRepository, toImplementation: GameRepositorySingleton);
To be honest I haven't tried this out. Tell me if it works. You might have to change extends to implements if the editor complains that GameRepository isn't a GameRepositorySingleton.
So I ended up doing this for now. As I need DI outside of redstone for now, I have an injector at top-level. Ideally I could share the injector with Redstone but that doesn't seem to be possible as far as I know. I've opened an issue here. So for now, I think the best way to share a singleton instante between redstone and my code would be something along these lines.
// in my top-level main()
ModuleInjector injector = new ModuleInjector([new Module()..bind(GameRepository)]);
// setup of redstone
GameRepository repo = injector.get(GameRepository);
app.addModule(new Module()..bind(GameRepository, toValue: repo));
// in my redstone resource
#app.Group('/games')
class GamesResource {
GameRepository gameRepository;
Games(this.gameRepository);
}
i'm looking for a larger example of dependency injection and how it can be implemented. If class A depends on class B and passes a reference of class C to B's constructor, must not class A also take a reference to class C in it's constructor? This means that the main method in the application should create all classes really, which sounds wierd?
I understand that using DI frameworks we can have it in XML files somehow, but that sounds like it could be hard to quickly see what type that really is instanciated? Especially if it a very large application.
You are correct and each DI framework has a different way of managing it.
Some use attributes on the properties etc to denote dependency and then "automagically" supply an instance of the correct type, while others (say castle windsor for .net) allow xml configuration, fluent or other methods for "wiring up" the dependency graph.
Also no, class A takes a built reference to an instance of B which was built using an instance of C. A needs to know nothing about C unless exposed via B.
public class C { }
public class B { public B(C c) { ... }}
public class A { public A(B b) { ... }}
// manual wireup
C c = new C();
B b = new B(c);
A a = new A(b);
// DI framework
InversionOfControlContainer container = new InversionOfControlContainer(... some configuration);
A a = container.ResolveInstanceOf<A>();
// container dynamically resolves the dependencies of A.
// it doesnt matter if the dependency chain on A is 100 classes long or 3.
// you need an instance of A and it will give you one.
Hope that helps.
to answer your question about classes A,B,and C, A only needs a reference to B.
Most DI frameworks do not require you to use XML for configuration. In fact, many people prefer not to use it. You can explicitly set things up in code, or use some kind of conventions or attributes for the container to infer what objects should fulfil dependencies.
Most DI frameworks have a facility for "lazy loading" to avoid the creation of every single class up front. Or you could inject your own "factory or builder" objects to create things closer to the time when they will be used
You've not said what language you are using. My example below is in C# using the Unity container. (obviously normally you would use interfaces rather than concrete types):
container = new UnityContainer();
container.RegisterType<C>();
container.RegisterType<B>();
A a = container.Resolve<A>();
here's a few examples from the PHP Language, hope this helps you understand
class Users
{
var $Database;
public function __construct(Database $DB)
{
$this->Database = $DB;
}
}
$Database = Database::getInstance();
$Users = new Users($Database);
From this example the new keyword is used in the method getInstance(), you can also do
$Users = new Users(Database::getInstance());
Or another way to tackle this is
class Users
{
/*Dependencies*/
private $database,$fileWriter;
public function addDependency($Name,$Object)
{
$this->$Name = $Object;
return $this;
}
}
$Users = new Users();
$Users->addDependency('database',new Database)->addDependency('fileWriter',new FileWriter);
Update:
to be honest, I never use Dependency Injection as all its doing is passing objects into classes to create a local scope.
I tend to create a global entity, and store objects within that so there only ever stored in 1 variable.
Let me show you a small example:
abstract class Registry
{
static $objects = array();
public function get($name)
{
return isset(self::$objects[$name]) ? self::$objects[$name] : null;
}
public function set($name,$object)
{
self::$objects[$name] = $object;
}
}
Ok the beauty of this type of class is
its very lightweight
it has a global scope
you can store anything such as resources
When your system loads up and your including and initializing all your objects you can just store them in here like so:
Registry::add('Database',new Database());
Registry::add('Reporter',new Reporter());
Where ever you are within your runtime you can just use this like a global variable:
class Users
{
public function getUserById($id)
{
$query = "SELECT * FROM users WHERE user_id = :id";
$resource = Registry::get("Database")->prepare($query);
$resource->bindParam(':id',$id,PDO::PARAM_INT);
if($resource->execute())
{
//etc
}else
{
Registry::get('Reporter')->Add("Unable to select getUserById");
}
}
}
i see this way of object passing is much cleaner
If anybody is still looking for a good example which shows DI without IoC Containers (poor man's DI) and also with IoC Container (Unity in this example) and registering the types in code and also in XML you can check this out: https://dannyvanderkraan.wordpress.com/2015/06/15/real-world-example-of-dependeny-injection/