I found this line of code in Aurelia Dialog
static inject = [DialogService];
This is the full class:
import {Prompt} from './prompt';
import {DialogService} from '../dialog-service';
export class CommonDialogs {
static inject = [DialogService];
constructor(dialogService){
this.dialogService = dialogService;
}
prompt(question){
return this.dialogService.open({viewModel:Prompt, model:question});
};
}
What is the static inject doing? I get that it is injecting the dialog service into the constructor. But why do it this way instead of the usual inject?
As the blog post you linked to mentions, static inject was the original way to do dependency injection. Once Babel started supporting decorators, we implemented the inject decorator to make Aurelia code look a little nicer. Under the covers, it simply adds the inject property to the class at runtime (https://github.com/aurelia/dependency-injection/blob/master/src/decorators.js#L13).
Related
In aurelia, is it possible to have a custom decorator automatically inject dependencies into the classes it decorates or does each decorated class need to inject the dependencies itself (at least in its constructor)?
In other words, is this the best that can be done:
Custom Decorator (my-decorator.js)
import {inject} from 'aurelia-framework';
import {Dependency} from 'dependency';
export function MyDecorator() {
return function(target) {
inject(Dependency)(target);
}
}
Decorated Class
import {MyDecorator} from "my-decorator";
#MyDecorator()
export class DecoratedClass {
constructor(dependency) {
this.dependency = dependency;
}
}
The inject property of a class is typically static. When most of the resolvers are used they simply "augment" the static inject property so that the container can resolve them using the specified resolver and pass them to the constructor. I don't know that a class decorator would help in this instance as it doesn't decorate the instance in anyway that I can think of, though I may be wrong.
If you are trying to create a new instance and still use DI to resolve dependencies you should look at the Factory resolver which supports this.
If you are trying to completely leave the constructor alone another idea would be to decorate a property or function instead which uses a complete separate property static customInject for example that resolves dependencies on the instance when invoked at start.
I'm pretty new to Aurelia (only been using it a few days) and I love it!
I know how to make a service with Aurelia, but how can I make that service a singleton that I can then share data with between multiple ViewModels?
Thanks
Just inject it
By default, the DI container assumes that everything is a singleton instance; one instance for the app. However, you can use a registration decorator to change this.
So I realized I was thinking about this too hard. I was trying to depend on the framework (Aurelia) to do all the work, but actually it was a simple ES6 class change that makes it an instance.
let instance = null;
export class SingletonService {
constructor() {
if(!instance) {
instance = this;
}
return instance;
}
}
I use an external service to provide properties, but want to make those properties available as #Named(..) vars. Trying to do this in a configure method fails with npe:
Names.bindProperties(binder(), myPropRetriever.getProperties());
is failing because the myPropRetriever isn't appearing until guice has done it's work. I can see why this makes sense - anyone know of any funky hacks that might work around though? Would be handy in this instance..
Thanks to durron597 for the pointer to the related question which gave me enough to figure out. The answer is to use a child injector to take action on the previous injectors output. Example below:
Injector propInjector = Guice.createInjector(new PropertiesModule());
PropertiesService propService = propInjector.getInstance(PropertiesService.class);
Injector injector = propInjector.createChildInjector(new MyModule(Objects.firstNonNull(propService.getProperties(), new Properties())));
Injector is now your injector for the remainder of the app.
And then in MyModule you can take action on the created objects:
public class MyModule extends AbstractModule {
private final Properties properties;
public MyModule(Properties properties){
this.properties=properties;
}
#Override
protected void configure() {
// export all the properties as bindings
Names.bindProperties(binder(), properties);
// move on to bindings
// bind(..);
}
}
In case it helps anyone else..!
Hi I have a problem with the structure of my code, it somehow goes into Circular Dependency. Here is an explanation of how my code looks like:
I have a ProjectA contains BaseProcessor and BaseProcessor has a reference to a class called Structure in ProjectB. Inside BaseProcessor, there is an instance of Structure as a variable.
In projectB there are someother classes such as Pricing, Transaction etc.
Every class in ProjectB has a base class called BaseStructure i.e. Structure, Pricing and Transaction classes all inherited from BaseStructure.
Now in Pricing and Transaction classes, I want to call a method in BaseProcessor class from BaseStructure class which causing Circular Dependency.
What I have tried is:
Using Unity, but I didn't figure out how to make it work because I try to use function like:
unityContainer.ReferenceType(IBaseProcessor, BaseProcessor)
in BaseStructure then it will need a reference of BaseProcessor which also cause Circular Dependency.
And I've also tried creating an interface of IBaseProcessor and create a function(the function I want to call) declaration in this interface. And let both BaseProcessor and BaseStructure inherit this interface. But how can I call the function in Pricing and Transaction class without create an instance of BaseProcessor?
Can anyone please tell me how to resolve this problem other than using reflection?
Any help will be much appreciated. Thanks :)
You could use the lazy resolution:
public class Pricing {
private Lazy<BaseProcessor> proc;
public Pricing(Lazy<BaseProcessor> proc) {
this.proc = proc;
}
void Foo() {
this.proc.Value.DoSomethin();
}
}
Note that you haven't to register the Lazy because Unity will resolve it by BaseProcessor registration.
Your DI container can't help solving the circular reference, since it is the dependency structure of the application that prevents objects from being created. Even without a DI container, you can't construct your object graphs without some special 'tricks'.
Do note that in most cases cyclic dependency graphs are a sign of a design flaw in your application, so you might want to consider taking a very close look at your design and see if this can't be solved by extracting logic into separate classes.
But if this is not an option, there are basically two ways of resolving this cyclic dependency graph. Either you need to fallback to property injection, or need to postpone resolving the component with a factory, Func<T>, or like #onof proposed with a Lazy<T>.
Within these two flavors, there are a lot of possible ways to do this, for instance by falling back to property injection into your application (excuse my C#):
public class BaseStructure {
public BaseStructure(IDependency d1) { ... }
// Break the dependency cycle using a property
public IBaseProcessor Processor { get; set; }
}
This moves the IBaseProcessor dependency from the constructor to a property and allows you to set it after the graph is constructed. Here's an example of an object graph that is built manually:
var structure = new Structure(new SomeDependency());
var processor = new BaseProcessor(structure);
// Set the property after the graph has been constructed.
structure.Processor = processor;
A better option is to hide the property inside your Composition Root. This makes your application design cleaner, since you can keep using constructor injection. Example:
public class BaseStructure {
// vanilla constructor injection here
public BaseStructure(IDependency d1, IBaseProcessor processor) { ... }
}
// Defined inside your Composition Root.
private class CyclicDependencyBreakingProcessor : IBaseProcessor {
public IBaseProcessor WrappedProcessor { get; set; }
void IBaseProcessor.TheMethod() {
// forward the call to the real processor.
this.WrappedProcessor.TheMethod();
}
}
Now instead of injecting the BaseProcessor into your Structure, you inject the CyclicDependencyBreakingProcessor, which will be further initialized after the construction of the graph:
var cyclicBreaker = new CyclicDependencyBreakingProcessor();
var processor = new BaseProcessor(new Structure(new SomeDependency(), cyclicBreaker));
// Set the property after the graph has been constructed.
cyclicBreaker.WrappedProcessor = processor;
This is basically the same as before, but now the application stays oblivious from the fact that there is a cyclic dependency that needed to be broken.
Instead of using property injection, you can also use Lazy<T>, but just as with the property injection, it is best to hide this implementation detail inside your Composition Root, and don't let Lazy<T> values leak into your application, since this just adds noise to your application, which makes your code more complex and harder to test. Besides, the application shouldn't care that the dependency injection is delayed. Just as with Func<T> (and IEnumerable<T>), when injecting a Lazy<T> the dependency is defined with a particular implementation in mind and we're leaking implementation details. So it's better to do the following:
public class BaseStructure {
// vanilla constructor injection here
public BaseStructure(IDependency d1, IBaseProcessor processor) { ... }
}
// Defined inside your Composition Root.
public class CyclicDependencyBreakingProcessor : IBaseProcessor {
public CyclicDependencyBreakingBaseProcessor(Lazy<IBaseProcessor> processor) {...}
void IBaseProcessor.TheMethod() {
this.processor.Value.TheMethod();
}
}
With the following wiring:
IBaseProcessor value = null;
var cyclicBreaker = new CyclicDependencyBreakingProcessor(
new Lazy<IBaseProcessor>(() => value));
var processor = new BaseProcessor(new Structure(new SomeDependency(), cyclicBreaker));
// Set the value after the graph has been constructed.
value = processor;
Up until now I only showed how to build up the object graph manually. When doing this using a DI container, you usually want to let the DI container build up the complete graph for you, since this yields a more maintainable Composition Root. But this can make it a bit more tricky to break the cyclic dependencies. In most cases the trick is to register the component that you want to break with a caching lifestyle (basically anything else than transient). Per Web Request Lifestyle for instance. This allows you to get the same instance in a lazy fashion.
Using the last CyclicDependencyBreakingProcessor example, we can create the following Unity registration:
container.Register<BaseProcessor>(new PerRequestLifetimeManager());
container.RegisterType<IStructure, Structure>();
container.RegisterType<IDependency, SomeDependenc>();
container.Register<IBaseProcessor>(new InjectionFactory(c =>
new CyclicDependencyBreakingProcessor(
new Lazy<IBaseProcessor>(() => c.GetInstance<BaseProcessor>())));
I've started playing with Wicket and I've chosen Guice as dependency injection framework. Now I'm trying to learn how to write a unit test for a WebPage object.
I googled a bit and I've found this post but it mentioned AtUnit so I decided to give it a try.
My WebPage class looks like this
public class MyWebPage extends WebPage
{
#Inject MyService service;
public MyWebPage()
{
//here I build my components and use injected object.
service.get(id);
....
}
}
I created mock to replace any production MyServiceImpl with it and I guess that Guice in hand with AtUnit should inject it.
Now the problems are:
AtUnit expects that I mark target object with #Unit - that is all right as I can pass already created object to WicketTester
#Unit MyWebPage page = new MyWebPage();
wicketTester.startPage(page);
but usually I would call startPage with class name.
I think AtUnit expects as well that a target object is market with #Inject so AtUnit can create and manage it - but I get an org.apache.wicket.WicketRuntimeException: There is no application attached to current thread main. Can I instruct AtUnit to use application from wicketTester?
Because I don't use #Inject at MyWebPage (I think) all object that should be injected by Guice are null (in my example the service reference is null)
I really can't find anything about AtUnit inside Wicket environment. Am I doing something wrong, am I missing something?
I don't know AtUnit but I use wicket with guice and TestNG. I imagine that AtUnit should work the same way. The important point is the creation of the web application with the use of guice.
Here how I bind all this stuff together for my tests.
I have an abstract base class for all my tests:
public abstract class TesterWicket<T extends Component> {
#BeforeClass
public void buildMockedTester() {
System.out.println("TesterWww.buildMockedTester");
injector = Guice.createInjector(buildModules());
CoachWebApplicationFactory instance =
injector.getInstance(CoachWebApplicationFactory.class);
WebApplication application = instance.buildWebApplication();
tester = new WicketTester(application);
}
protected abstract List<Module> buildModules();
The initialization is done for every test class. The subclass defines the necessary modules for the test in the buildModules method.
In my IWebApplicationFactory I add the GuiceComponentInjector. That way, after all component instantiation, the fields annotated with #Inject are filled by Guice:
public class CoachWebApplicationFactory implements IWebApplicationFactory {
private static Logger LOG = LoggerFactory.getLogger(CoachWebApplicationFactory.class);
private final Injector injector;
#Inject
public CoachWebApplicationFactory(Injector injector) {
this.injector = injector;
}
public WebApplication createApplication(WicketFilter filter) {
WebApplication app = injector.getInstance(WebApplication.class);
Application.set(app);
app.addComponentInstantiationListener(new GuiceComponentInjector(app, injector));
return app;
}
}