I need to find a way to get an instance of DataProcessingEngine without calling it's constractor.
I am trying to find a way to do so using the registered DataProcessingEngine in composition object (please see the following code). But I could not find a way to do so.
Anyone have a suggestion? Thanks in advance.
public class Composer : IUserComposer
{
public void Compose(Composition composition)
{
composition.Register<IDataProcessingEngine, DataProcessingEngine>(Lifetime.Singleton);
//DataProcessingEngine dataProcessing = compostion.Resolve<IDataProcessingEngine>()??//no resolve function exists in Umbraco.Core.Composing
SaveImagesThread(dataProcessingEngine);
}
public Task SaveImagesThread(IDataProcessingEngine dataProcessingEngine)//TODO - decide async
{
string dataTimerTime = WebConfig.SaveProductsDataTimer;
double time = GetTimeForTimer(dataTimerTime);
if (time > 0)
{
var aTimer = new System.Timers.Timer(time);
aTimer.Elapsed += new ElapsedEventHandler(dataProcessingEngine.SaveImages);
aTimer.Start();
}
return default;
}
}
For all of you who are looking for a way to call a function (that's defined in another class in your code, an Engine or ...) from the composer(where the app starts) and want to avoid calling this function's class' constractor. I've found another way to do so:
public class QueuePollingHandler
{
[RuntimeLevel(MinLevel = RuntimeLevel.Run)]
public class SubscribeToQueuePollingHandlerComponentComposer :
ComponentComposer<SubscribeToQueuePollingHandler>
{ }
public class SubscribeToQueuePollingHandler : IComponent
{
private readonly IDataProcessingEngine _dataProcessingEngine;
public SubscribeToQueuePollingHandler(IDataProcessingEngine
dataProcessingEngine)
{
_dataProcessingEngine = dataProcessingEngine;
SaveImagesThread(_dataProcessingEngine);
}
public void SaveImagesThread(IDataProcessingEngine
dataProcessingEngine)
{
....
}
}
And the logic explenation: You create a class (SubscribeToQueuePollingHandlerComponentComposer from the example) and define its base class to be ComponentComposer<Class_that_inherits_IComponent>.
And when you start the application you could see that it gets to the registered class' constractor (SubscribeToQueuePollingHandler constructor).
That's the way that I found to be able to call a function right when the application starts without needing to call its class constractor and actualy use dependency injection.
Related
Hi I am just been looking at AutoFac and following their getting-started tutorial
http://autofac.readthedocs.org/en/latest/getting-started/index.html
having followed it and understanding how their services work I wanted to try to create a new implementation on the same interface type
builder.RegisterType<TodayWriter>().As<IDateWriter>();
builder.RegisterType<TomorrowWriter>().As<IDateWriter>();
Both implentations contain the same code
public class TomorrowWriter : IDateWriter
{
private IOutput _output;
public TomorrowWriter(IOutput output)
{
this._output = output;
}
public void WriteDate()
{
this._output.Write(DateTime.Today.AddDays(1).ToShortDateString());
}
}
So TodaysWriter is the same apart from the WriteDate method displaying
this._output.Write(DateTime.Today.ToShortDateString());
instead.
So now using the application, how do I determine what implementation to use as both methods are called WriteDate()
using(var scope = Container.BeginLifetimeScope())
{
var writer = scope.Resolve<IDateWriter>();
// Is this using todaysWriter or TomorrowWriter?
writer.WriteDate();
}
Am I using this wrong?
Thanks
To differentiate between different implementations of the same interface look at named and keyed services in the docs.
Alternatively you can roll your own by registering a DateWriterFactory and having a method on that to get a specific IDateWriter implementation. something like:
public class DateWriterFactory
{
IDateWriter GetWriter(string writerName)
{
if (writername=="TodayWriter")
return new TodayWriter();
if (writername=="TomorrowWriter")
return new TomorrowWriter();
}
}
obviously the implementation of the factory could be as complex or as simple as you need. Or you could just have methods to get the fixed writers rather than pass in a string.
I am about to switch from Windsor to Structuremap for an existing project with ~100 registered components (mostly singletons).
All components inherit from a common base class that provides logging and health tracking and for this reason, contains a "Name" property used to identify component instances.
With Windsor, it was possible to set the component's Name property to the name that was used to register the component in the IOC container (We used a Facility for this).
My question: Is something like this possible with Structuremap?
(I dream of a call to c.For<IFoo>.Use<Bar>.Named("Doe") that magically results in instanceOfBar.Name = "Doe" somewhere.)
Here is what I tried:
using System;
using StructureMap;
using StructureMap.Interceptors;
using System.Diagnostics;
namespace ConsoleApplication1
{
interface IServiceA { }
interface IServiceB { }
class Base
{
public string Name { get; set; }
}
class ComponentA : Base, IServiceA { }
class ComponentB : Base, IServiceB
{
public ComponentB(IServiceA serviceA)
{
this.ServiceA = serviceA;
}
public IServiceA ServiceA { get; private set; }
}
class SetNameInterceptor : TypeInterceptor
{
public bool MatchesType(Type type) { return true; }
public object Process(object target, IContext context)
{
// *** Any other way? This does not work...
string name = context.BuildStack.Current != null ? context.BuildStack.Current.Name : context.RequestedName;
((Base)target).Name = name;
return target;
}
}
class Program
{
static void Main(string[] args)
{
Container container = new Container(c =>
{
c.RegisterInterceptor(new SetNameInterceptor());
c.For<IServiceA>().Use<ComponentA>().Named("A");
c.For<IServiceB>().Use<ComponentB>().Named("B");
});
var b = container.GetInstance<IServiceB>();
// both Fail:
Debug.Assert(((ComponentB)b).Name == "B");
Debug.Assert(((ComponentA)((ComponentB)b).ServiceA).Name == "A");
}
}
}
The above obviously does not work, I tried several variations but had no luck. The registered name of the target object does not seem to be consistently reachable via IContext.
My second best approach would be to define a new "NamedComponent(...)" extension method that resolves to Named(name).WithProperty(x => x.Name).EqualTo(name), but I wonder if this can be avoided to keep component registration as "structuremap-like" as possible?
Am I missing something?
I've never used WithProperty before but if it works the way I'd expect it should do the trick for you.
I think I would favor using EnrichWith though. Something like:
c.For<IFoo>().Use<Foo>().Named(name).EnrichWith(f => f.Name = name);
EnrichWith is a bit more explicit about what it's doing IMO, and lets you call any code on your instance before returning it to the caller. I like that this lets you do a straightforward assignment as well.
There is also a more complex handler you can use with EnrichWith that gives access to the context of the request - this would allow you to do something like this:
c.For<IFoo>().Use<Foo>().Named(name)
.EnrichWith((c, i) => {
i.Name = c.RequestedName;
return i;
});
This may be overkill for your situation but the contextual awareness can be pretty useful.
Imagine there is a Customer class with an instance Load() method.
When the Load() method is called, it retrieves order details by e.g.
var orders = Order.GetAll(customerId, ...);
GetAll() is a static method of the Order class and the input parameters are fields defined in the Customer class.
As you can see, Order is a dependency of the Customer class, however, I can't just create an IOrder and inject it there as interfaces can't have static methods.
Therefore, the question is how could I introduce dependency injection in this example?
I don't want to make GetAll() an instance method since it's a static method and need to keep it that way.
For example, I have used utility classes in my design, most of which just contain static methods.
If you must keep the static method, I would wrap the static calls in a Repository object.
Like this:
interface IOrderRepository {
IEnumerable<IOrder> GetAll(customerId, ..);
}
class OrderRepository : IOrderRepository {
IEnumerable<IOrder> GetAll(customerId, ...)
{
Order.GetAll(customerId,...); // The original static call.
}
}
Now you inject this repository into your Customer class.
(I'm assuming you're doing this so you can inject fake IOrders at runtime for testing purposes. I should say that in general, static methods are a serious obstacle to testing.)
Seeing as your aggregate root for fetching orders is your customer model I would strongly advise you create a customer repository and inject that to whatever service requires it.
Here is an example:
public class CustomerService
{
private readonly ICustomerRepository _customerRepository;
public CustomerService(ICustomerRepository customerRepository)
{
if (customerRepository == null)
{
throw new ArgumentNullException("customerRepository");
}
_customerRepository = customerRepository;
}
public IEnumerable<IOrder> GetOrdersForCustomerId(int customerId)
{
return _customerRepository.GetOrdersForCustomerId(customerId);
}
}
public interface ICustomerRepository
{
IEnumerable<IOrder> GetOrdersForCustomerId(int customerId);
}
class CustomerRepository : ICustomerRepository
{
public IEnumerable<IOrder> GetOrdersForCustomerId(int customerId)
{
throw new NotImplementedException();
}
}
Function Pointer Injection
TLDR:
Inject a function pointer into the Customer class. The value of this function pointer can be Order.GetAll in production, and MockOrder.GetAll in tests.
EXAMPLE:
The dependency (problematic static function we depend on):
class Order {
static func GetAll() -> [Order] {
var orders = ... // Load from production source
return orders
}
}
Our dependent class (depends on static function):
class Customer {
func Init(getAllOrdersFunction) { // Arg is a func pointer
self.getAllOrdersFunction = getAllOrdersFunction
}
func Load() {
var orders = self.getAllOrdersFunction()
// Do stuff...
}
}
Production client class (performs the dependency injection):
class BusinessLogicManager {
func DoBusinessLogic() {
var customer = Customer(Order.GetAll) // Prod func injected here
customer.Load()
// Do stuff...
}
}
Testing client class (how unit test can inject a fake dependency):
class CustomerUnitTests {
static func GetFakeOrders() {
var orders = ... // Hardcoded test data
return orders
}
func TestLoad() {
var customer = Customer(CustomerUnitTests.GetFakeOrders) // Fake func injected here
customer.Load()
// Verify results given known behavior of GetFakeOrders
}
}
DISCUSSION:
How you actually inject the "function pointer" will depend on the syntax and features available in your language. Here I'm just talking about the general concept.
This isn't exactly a pretty solution. It would probably be easier if you can change GetAll to be an instance method (perhaps by introducing an OrdersLoader object, or by using Paul Phillips' answer). But if you really want to keep it as a static function, then this solution will work.
How do I handle classes with static methods with Ninject?
That is, in C# one can not have static methods in an interface, and Ninject works on the basis of using interfaces?
My use case is a class that I would like it to have a static method to create an
unpopulated instance of itself.
EDIT 1
Just to add an example in the TopologyImp class, in the GetRootNodes() method, how would I create some iNode classes to return? Would I construct these with normal code practice or would I somehow use Ninject? But if I use the container to create then haven't I given this library knowledge of the IOC then?
public interface ITopology
{
List<INode> GetRootNodes();
}
public class TopologyImp : ITopology
{
public List<INode> GetRootNodes()
{
List<INode> result = new List<INode>();
// Need code here to create some instances, but how to without knowledge of the container?
// e.g. want to create a few INode instances and add them to the list and then return the list
}
}
public interface INode
{
// Parameters
long Id { get; set; }
string Name { get; set; }
}
class NodeImp : INode
{
public long Id
{
get { throw new NotImplementedException(); }
set { throw new NotImplementedException(); }
}
public string Name
{
get { throw new NotImplementedException(); }
set { throw new NotImplementedException(); }
}
}
// Just background to highlight the fact I'm using Ninject fine to inject ITopology
public partial class Form1 : Form
{
private ITopology _top;
public Form1()
{
IKernel kernal = new StandardKernel(new TopologyModule());
_top = kernal.Get<ITopology>();
InitializeComponent();
}
}
If you're building a singleton or something of that nature and trying to inject dependencies, typically you instead write your code as a normal class, without trying to put in lots of (probably incorrect) code managing the singleton and instead register the object InSingletonScope (v2 - you didnt mention your Ninject version). Each time you do that, you have one less class that doesnt surface its dependencies.
If you're feeling especially bloody-minded and are certain that you want to go against that general flow, the main tools Ninject gives you is Kernel.Inject, which one can use after you (or someone else) has newd up an instance to inject the dependencies. But then to locate one's Kernelm you're typically going to be using a Service Locator, which is likely to cause as much of a mess as it is likely to solve.
EDIT: Thanks for following up - I see what you're after. Here's a hacky way to approximate the autofac automatic factory mechanism :-
/// <summary>
/// Ugly example of a not-very-automatic factory in Ninject
/// </summary>
class AutomaticFactoriesInNinject
{
class Node
{
}
class NodeFactory
{
public NodeFactory( Func<Node> createNode )
{
_createNode = createNode;
}
Func<Node> _createNode;
public Node GenerateTree()
{
return _createNode();
}
}
internal class Module : NinjectModule
{
public override void Load()
{
Bind<Func<Node>>().ToMethod( context => () => Kernel.Get<Node>() );
}
}
[Fact]
public void CanGenerate()
{
var kernel = new StandardKernel( new Module() );
var result = kernel.Get<NodeFactory>().GenerateTree();
Assert.IsType<Node>( result );
}
}
The ToMethod stuff is a specific application of the ToProvider pattern -- here's how you'd do the same thing via that route:-
...
class NodeProvider : IProvider
{
public Type Type
{
get { return typeof(Node); }
}
public object Create( IContext context )
{
return context.Kernel.Get<Node>();
}
}
internal class Module : NinjectModule
{
public override void Load()
{
Bind<Func<Node>>().ToProvider<NodeProvider>();
}
}
...
I have not thought this through though and am not recommending this as A Good Idea - there may be far better ways of structuring something like this. #Mark Seemann? :P
I believe Unity and MEF also support things in this direction (keywords: automatic factory, Func)
EDIT 2: Shorter syntax if you're willing to use container-specific attributes and drop to property injection (even if Ninject allows you to override the specific attributes, I much prefer constructor injection):
class NodeFactory
{
[Inject]
public Func<Node> NodeFactory { private get; set; }
public Node GenerateTree()
{
return NodeFactory();
}
}
EDIT 3: You also need to be aware of this Ninject Module by #Remo Gloor which is slated to be in the 2.4 release
EDIT 4: Also overlapping, but not directly relevant is the fact that in Ninject, you can request an IKernel in your ctor/properties and have that injected (but that doesn't work directly in a static method).
public class TheController : Controller
{
IThe the;
public TheController( IThe the)
{
//when User.IsInRole("r1") The1 should be injected else r2
this.the = the;
}
}
public class The1 : IThe{}
public class The2 : IThe{}
//anybody knows a good way of doing this ?
IHandlerSelector is the way to go. See this post for an example of usage.
Alternatively if you prefer AutoFac-like experience you can use factory for that:
container.Register(Component.For<IThe>().UsingFactoryMethod(
c => HttpContext.Current.User.IsInRole("r1") ?
c.Resolve<IThe>("r1") :
c.Resolve<IThe>("r2"));
Or if you want to use specific IThe just in one context, you can use DynamicParameters:
container.Register(Component.For<TheFactory>().Lifestyle.Transient.DynamicParameters(
(c, d) => HttpContext.Current.User.IsInRole("r1") ?
d["the"] = c.Resolve<IThe>("r1") :
c.Resolve<IThe>("r2"));
However the most correct way of doing this is IHandlerSelector
The container-agnostic approach obviously employs an Abstract Factory:
public interface ITheFactory
{
IThe Create(IPrincipal user);
}
You can take a dependency on ITheFactory instead of IThe:
public class TheController : Controller
{
private readonly IThe the;
public TheController(ITheFactory theFactory)
{
if (theFactory == null)
{
throw new ArgumentNullException("theFactory");
}
this.the = theFactory.Create(this.User);
}
}
I can't really remember if this.User is populated at this time, but if it isn't, you can just keep a reference to the factory and lazily resolve your dependency the first time it's requested.
However, Controller.User is a bit special because it ought to be available as Thread.CurrentPrincipal as well. This means that in this special case you don't actually have to introduce an Abstract Factory. Instead, you can write a Decorator that performs the selection every time it's used:
public class UserSelectingThe : IThe
{
private readonly IThe the1;
private readonly IThe the2;
public UserSelectingThe(IThe the1, IThe the2)
{
if (the1 == null)
{
throw new ArgumentNullException("the1");
}
if (the2 == null)
{
throw new ArgumentNullException("the2");
}
this.the1 = the1;
this.the2 = the2;
}
// Assuming IThe defines the Foo method:
public Baz Foo(string bar)
{
if (Thread.CurrentPrincipal.IsInRole("r1"))
{
return this.the1.Foo(bar);
}
return this.the2.Foo(bar);
}
}
In this case, you would be able to use your original TheController class unchanged.
In Autofac:
var builder = new ContainerBuilder();
// Give the different implementations names
builder.RegisterType<The1>.Named<IThe>("r1");
builder.RegisterType<The2>.Named<IThe>("r2");
// Use a function for the default IThe
builder.Register(
c => HttpContext.Current.User.IsInRole("r1") ?
c.Resolve<IThe>("r1") :
c.Resolve<IThe>("r2"))
.As<IThe>()
.ExternallyOwned();
If you have a lot of roles, you can use a method instead of the inline expression, e.g.:
builder.Register(c => ChooseTheImplementation(c))
(BTW, The "ExternallyOwned" modifier tells the container that the result of the function is disposed elsewhere, e.g. via the concrete components. You can usually leave it out but it makes good documentation :))