c# - 如何将 DbContext 实现注入(inject) Prism ViewModel 构造函数？

Question

我正在使用 Unity 和 Entity Framework 开发 WPF Prism 应用程序。我希望在构建 ViewModel 时注入(inject)我的自定义 DbContext，这样我就可以在 ViewModel 的整个生命周期中使用它。 DbContext 类所在的模块在 Bootstrapper 中注册，DbContext 类型在 Module.Initialize() 期间注册。

综上所述，在尝试构造注入(inject) DbContext 的 ViewModel 时会抛出运行时错误。它说 IDbConnection 需要注册。当我向模块注册它时，它会说 DbConnection 是一个抽象类，无法构造。关于应该如何注册 DbContext，肯定有一些我不知道的事情。

这是在模块中注册类型的位置:

public class SharedResourcesModule : IModule
{
    IUnityContainer container;


    public SharedResourcesModule(IUnityContainer container)
    {
        this.container = container;
    }


    public void Initialize()
    {
        container.RegisterType<IAuthenticationService, AuthenticationService>();
        container.RegisterType<IDataBaseContext, EFDbContext>();
    }
}

还有一个 ViewModel 构造函数的例子:

public class ProductContextResultViewModel : ViewModelBase
{
    public ProductContextResultViewModel(IDataBaseContext dataBaseContext)
    {
        this.DataBaseContext = dataBaseContext as EFDbContext;
    }


    private EFDbContext DataBaseContext { get; set; }
}

如果我可以提供任何其他详细信息，请告诉我!

异常详情如下:

Microsoft.Practices.ServiceLocation.ActivationException 未被用户代码处理 HResult=-2146233088 消息=尝试获取对象类型的实例时出现激活错误，键为“ProductContextResultView” 源=Microsoft.Practices.ServiceLocation 堆栈跟踪: 在 Microsoft.Practices.ServiceLocation.ServiceLocatorImplBase.GetInstance(类型 serviceType，字符串键)在 c:\Projects\CommonServiceLocator\main\Microsoft.Practices.ServiceLocation\ServiceLocatorImplBase.cs:line 53 在 Microsoft.Practices.ServiceLocation.ServiceLocatorImplBase.GetInstance[TService](字符串键)在 c:\Projects\CommonServiceLocator\main\Microsoft.Practices.ServiceLocation\ServiceLocatorImplBase.cs:line 103 在 Microsoft.Practices.Prism.Regions.RegionNavigationContentLoader.CreateNewRegionItem(字符串 candidateTargetContract) 内部异常:Microsoft.Practices.Unity.ResolutionFailedException HResult=-2146233088 Message=解析依赖失败，类型=“System.Object”，名称=“ProductContextResultView”。异常发生在:解析时。

异常是:InvalidOperationException - 当前类型 System.Data.Common.DbConnection 是一个抽象类，无法构造。您是否缺少类型映射？

发生异常时，容器是:

正在解析 ContextResultsPane.ProductContextResult.ProductContextResultView、ProductContextResultView(从 System.Object、ProductContextResultView 映射) 解析构造函数 ContextResultsPane.ProductContextResult.ProductContextResultView(ContextResultsPane.ProductContextResult.ProductContextResultViewModel viewModel) 的参数“viewModel” 解析 ContextResultsPane.ProductContextResult.ProductContextResultViewModel，(无) 解析构造函数 ContextResultsPane.ProductContextResult.ProductContextResultViewModel(SharedResources.DataAccess.IDataBaseContext dataBaseContext) 的参数“dataBaseContext” 解析 SharedResources.DataAccess.EFDbContext，(无)(从 SharedResources.DataAccess.IDataBaseContext 映射，(无)) 解析构造函数 SharedResources.DataAccess.EFDbContext(System.Data.Common.DbConnection connection) 的参数“连接” 解析 System.Data.Common.DbConnection，(无)

   Source=Microsoft.Practices.Unity
   NameRequested=ProductContextResultView
   TypeRequested=Object
   StackTrace:
        at Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, Object existing, String name, IEnumerable`1 resolverOverrides)
        at Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, String name, IEnumerable`1 resolverOverrides)
        at Microsoft.Practices.Unity.UnityContainer.Resolve(Type t, String name, ResolverOverride[] resolverOverrides)
        at Microsoft.Practices.Prism.UnityExtensions.UnityServiceLocatorAdapter.DoGetInstance(Type serviceType, String key)
        at Microsoft.Practices.ServiceLocation.ServiceLocatorImplBase.GetInstance(Type serviceType, String key) in c:\Projects\CommonServiceLocator\main\Microsoft.Practices.ServiceLocation\ServiceLocatorImplBase.cs:line 49
   InnerException: System.InvalidOperationException
        HResult=-2146233079
        Message=The current type, System.Data.Common.DbConnection, is an abstract class and cannot be constructed. Are you missing a type mapping?
        Source=Microsoft.Practices.Unity
        StackTrace:
             at Microsoft.Practices.ObjectBuilder2.DynamicMethodConstructorStrategy.ThrowForAttemptingToConstructAbstractClass(IBuilderContext context)
             at lambda_method(Closure , IBuilderContext )
             at Microsoft.Practices.ObjectBuilder2.DynamicBuildPlanGenerationContext.<>c__DisplayClass1.<GetBuildMethod>b__0(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.DynamicMethodBuildPlan.BuildUp(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.BuilderContext.NewBuildUp(NamedTypeBuildKey newBuildKey)
             at Microsoft.Practices.Unity.ObjectBuilder.NamedTypeDependencyResolverPolicy.Resolve(IBuilderContext context)
             at lambda_method(Closure , IBuilderContext )
             at Microsoft.Practices.ObjectBuilder2.DynamicBuildPlanGenerationContext.<>c__DisplayClass1.<GetBuildMethod>b__0(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.DynamicMethodBuildPlan.BuildUp(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.BuilderContext.NewBuildUp(NamedTypeBuildKey newBuildKey)
             at Microsoft.Practices.Unity.ObjectBuilder.NamedTypeDependencyResolverPolicy.Resolve(IBuilderContext context)
             at lambda_method(Closure , IBuilderContext )
             at Microsoft.Practices.ObjectBuilder2.DynamicBuildPlanGenerationContext.<>c__DisplayClass1.<GetBuildMethod>b__0(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.DynamicMethodBuildPlan.BuildUp(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.BuilderContext.NewBuildUp(NamedTypeBuildKey newBuildKey)
             at Microsoft.Practices.Unity.ObjectBuilder.NamedTypeDependencyResolverPolicy.Resolve(IBuilderContext context)
             at lambda_method(Closure , IBuilderContext )
             at Microsoft.Practices.ObjectBuilder2.DynamicBuildPlanGenerationContext.<>c__DisplayClass1.<GetBuildMethod>b__0(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.DynamicMethodBuildPlan.BuildUp(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context)
             at Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context)
             at Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, Object existing, String name, IEnumerable`1 resolverOverrides)
        InnerException: 

Answer 1

Glen Thomas 的指导帮助我进行了更多阅读，结果证明 Unity 默认使用最冗长的构造函数。这是问题的核心，因为我有一个构造函数需要传递 DbConnection 以进行单元测试。

为了强制 Unity 使用默认构造函数，我更改了这个...

container.RegisterType<IDataBaseContext, EFDbContext>();

...为此...

container.RegisterType<IDataBaseContext, EFDbContext>(new InjectionConstructor());

更改后它按预期工作!