Dependency Injection

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Angel uses a container hierarchy for DI. Dependency injection makes it easier to build applications with multiple moving parts, because logic can be contained in one location and reused at another place in your application.
Adding a Singleton
Future<void> myPlugin(Angel app) async  {
  app.container.registerSingleton(SomeClass("foo"));
  app.container.registerSingleton<SomeAbstractClass>(MyImplClass());
  app.container.registerFactory((_) => SomeClass("foo"));
  app.container.registerLazySingleton((_) => SomeOtherClass());
  app.container.registerNamedSingleton('yes', Yes());
}
You can also inject within a RequestContext, as each one has a controller property that extends from the app's global container.
Accessing these injected properties is easy, and strongly typed:
// Inject types.
var todo = req.container.make<Todo>();
print(todo.isComplete);
​
// Or by name
var db = await req.container.findByName<Db>('database');
var collection = db.collection('pets');
In Routes and Controllers
In Angel 2.0, by wrapping a function in a call to ioc, you can automatically inject the dependencies of any route handler.
app.get("/some/class/text", ioc((SomeClass singleton) => singleton.text)); // Always "foo"
​
app.post("/foo", ioc((SomeClass singleton, {Foo optionalInjection}));
​
@Expose("/my/controller")
class MyController extends Controller {
​
  @Expose("/bar")
  // Inject classes from container, request parameters or the request/response context :)
  bar(SomeClass singleton, RequestContext req) => "${singleton.text} bar"; // Always "foo bar"
​
  @Expose("/baz")
  baz({Foo optionalInjection});
}
As you can imagine, this is very useful for managing things such as database connections.
configureServer(Angel app) async {
  var db = Db("mongodb://localhost:27017/db");
  await db.open();
  app.container.registerSingleton(db);
}
​
@Expose("/users")
class ApiController extends Controller {
  @Expose("/:id")
  fetchUser(String id, Db db) => db.collection("users").findOne(where.id(ObjectId.fromHexString(id)));
}
Dependency-Injected Controllers
Controllers have dependencies injected without any additional configuration by you. However, you might want to inject dependencies into the constructor of your controller.
@Expose('/controller')
class MyController {
  final AngelAuth auth;
  final Db db;
​
  MyController(this.auth, this.db);
​
  @Expose('/login')
  login() => auth.authenticate('local');
}
​
main() async {
  // At some point in your application, register necessary dependencies as singletons...
  app.container.registerSingleton(auth);
  app.container.registerSingleton(db);
​
  // Create the controller with injected dependencies
  await app.mountController<MyController>();
}
Enabling dart:mirrors or other Reflection
By default, Angel will use the EmptyReflector() to power its Container instances, which has no support for dart:mirrors, so that it can be used in contexts where Dart reflection is not available.
However, by using a different Reflector, you can use the full power of Angel's DI system. angel init projects use the MirrorsReflector() by default.
If your application is using any sort of functionality reliant on annotations or reflection, either include the MirrorsReflector, or use a static reflector variant.
The following use cases require reflection:
Use of Controllers, via @Expose() or @ExposeWS()
Use of dependency injection into constructors, whether in controllers or plain container.make calls
Use of the ioc function in any route
The MirrorsReflector from package:angel_container/mirrors.dart is by far the most convenient pattern, so use it if possible.
However, the following alternatives exist:
Generation via package:angel_container_generator
Creating an instance of StaticReflector
Manually implementing the Reflector interface (cumbersome; not recommended)
Requests & Responses
Basic Routing
Last modified 3yr ago
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On this page
Adding a Singleton
In Routes and Controllers
Dependency-Injected Controllers
Enabling dart:mirrors or other Reflection