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    <p>Dependencies should be resolved in cascade down from the top layer classes, not using static or singleton container in constructors.</p> <p>Check this <a href="http://www.devtrends.co.uk/blog/how-not-to-do-dependency-injection-the-static-or-singleton-container" rel="nofollow">link</a>.</p> <p>If your app does not provide any hook into the pipeline to resolve the dependencies (as <code>Unity.Mvc3</code> does with controllers) the best aproach is resolve the <code>Manager</code> (your top layer class) class through Unity (you must register it first) and let the DI container inject <code>IRepository</code>. This alows you to keep the static/singleton container in one place and keep things under control. No other layer in your app should know anything about DI container.</p> <p>An example of resolving complete dependency graph could be the next piece of code:</p> <pre><code>Public Class ClasificationManagement //application layer service, top layer class Implements IClasificationManagement Private _servicio As IClasificacionesService //inject domain serice for bussines Private _repositorio As IClasificationRepository //inject repository for perisitence Public Sub New(ByVal servicio As IClasificacionesService, ByVal repositorio As IClasificationRepository) _servicio = servicio _repositorio = repositorio End Sub Public sub SwapDescrition(ByVal clasificationOrigenID As String, ByVal clasificationDestinoID As String) Implements IClasificationManagement. SwapDescrition //code using domain services and repositories End sub Public class ClasificacionesService implements IClasificacionesService private _tracer as ITracer //inject tracer to service domain public sub new(tracer as ITracer) _tracer = tracer end sub //not relevant code using ITracer End Class </code></pre> <p>With the prorper configuration of Unity in XML or runtime I just need to resolve ClasificationManagement and Unity do the dirty work of resolving all dependecy chain.</p> <pre><code>//resolve manager manager = ServiceLocator.Current.GetInstance(Of IClasificationManager)() //use manager, all dependencies (bussines service, repositories, tracers) were injected by Unity manager.SwapDescrition("123-ABC", "456-DEF") </code></pre> <p>For Unity config I like xml configuration because you can change the dependencies and no compilantion is needed. Just include this function somewhere in the initialization logic of your app.</p> <pre><code>Imports Microsoft.Practices.Unity Imports Microsoft.Practices.Unity.Configuration Imports Microsoft.Practices.ServiceLocation Private Sub InitServiceLocator() Dim container As IUnityContainer = New UnityContainer() container.LoadConfiguration() //read xml config //container.RegisterType&lt;Of ...&gt;(...) //config in runtime Dim provider = New UnityServiceLocator(container) ServiceLocator.SetLocatorProvider(Function() provider) End Sub </code></pre> <p>A XML config should looks like:</p> <pre><code>&lt;?xml version="1.0" encoding="utf-8" ?&gt; &lt;unity xmlns="http://schemas.microsoft.com/practices/2010/unity"&gt; &lt;alias alias="IClasificationManagement" type="AppPrincipal.IClasificationManagement, AppPrincipal" /&gt; &lt;alias alias="IClasificationRepository" type="X509ValDAL.IClasificationRepository, X509ValDAL" /&gt; &lt;alias alias="IClasificacionesService" type="Entidades.IClasificacionesService, Entidades" /&gt; &lt;alias alias="IUnitOfWork" type="X509ValDAL.IUnitOfWork, X509ValDAL" /&gt; &lt;alias alias="ObjectContext" type="System.Data.Objects.ObjectContext, System.Data.Entity, Version=3.5.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" /&gt; &lt;alias alias="ClasificationManagement" type="AppPrincipal.ClasificationManagement, AppPrincipal" /&gt; &lt;alias alias="ClasificationRepository" type="X509ValDAL.ClasificationRepository, X509ValDAL" /&gt; &lt;alias alias="ClasificacionesService" type="Entidades.ClasificacionesService, Entidades" /&gt; &lt;alias alias="UnitOfWork" type="X509ValDAL.UnitOfWork, X509ValDAL" /&gt; &lt;alias alias="X509VALEntities" type="Entidades.X509VALEntities, Entidades" /&gt; &lt;assembly name="AppPrincipal" /&gt; &lt;assembly name="X509ValDAL" /&gt; &lt;assembly name="Entidades" /&gt; &lt;assembly name="System.Data.Entity" /&gt; &lt;namespace name="AppPrincipal" /&gt; &lt;namespace name="X509ValDAL" /&gt; &lt;namespace name="Entidades" /&gt; &lt;namespace name="System.Data.Objects" /&gt; &lt;container&gt; &lt;register type="IClasificationManagement" mapTo="ClasificationManagement"&gt; &lt;constructor&gt; &lt;param name="servicio"&gt; &lt;dependency/&gt; &lt;/param&gt; &lt;param name="repositorio"&gt; &lt;dependency/&gt; &lt;/param&gt; &lt;/constructor&gt; &lt;/register&gt; &lt;register type="IClasificationRepository" mapTo="ClasificationRepository"&gt; &lt;constructor&gt; &lt;param name="uow"&gt; &lt;dependency/&gt; &lt;/param&gt; &lt;/constructor&gt; &lt;/register&gt; &lt;register type="IClasificacionesService" mapTo="ClasificacionesService" /&gt; TODO: Inject ITracer &lt;register type="ObjectContext" mapTo="X509VALEntities" /&gt; &lt;register type="IUnitOfWork" mapTo="UnitOfWork" &gt; &lt;constructor&gt; &lt;param name="context"&gt; &lt;dependency /&gt; &lt;/param&gt; &lt;/constructor&gt; &lt;/register&gt; &lt;/container&gt; &lt;/unity&gt; </code></pre> <p>I hope this example hepls you to understand the phylosophy of DI. Even when I use a static container (ServiceLocator); the container is used just to load top level layer classes to avoid servicelocator antipattern.</p>
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    1. COI checked the link, and I see how I am supposed to only have my top layer know about the container - I am not sure of how to "resolve in cascade down" though, would you mind providing an example? :)
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    2. COThanks for the edit - I got that part, but could you show me where you tell the application to use a specific implementation? Where do you register to your container?
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    3. COI'm sorry, but this is confusing me even more.. So by using XML, you can inject the members without using a Dependency atrribute? How does it work?
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