Question

我正在按照以下教程快速学习代码。 Code First to a New Database

直到本教程的第4步：我尝试运行代码时出现问题。我在以下代码中遇到以下异常......

    foreach (var item in query)
    {
        Console.WriteLine(item.Name);
    }
    {"Exception has been thrown by the target of an invocation."}

内部异常

    {"Access is denied: 'CodeFastNewDatabase.Program+Blog'.":""}

当我尝试检查db变量属性时，很多人都有调试错误说“函数求值需要所有线程运行” 代码在我的本地数据库中创建数据库，同时插入值。

如果我删除属性Blog和Post中的虚拟说明符

，我可以解决这个问题

    public virtual List<Post> Posts { get; set; }
    public virtual Blog Blog { get; set; }

我的其他项目也面临同样的例外。许多属性显示“功能评估需要所有线程运行”

我正在使用Entity Framework 6.0

编辑：

Blog是DbContext对象的属性，我已经在程序类的main函数中初始化了。然后在上下文中添加博客，然后保存它。创建/更新了数据库并插入了我的给定值。代码与示例链接中的代码相同。

[堆栈追踪] 这是我捕获的堆栈跟踪。

   at System.Environment.GetStackTrace(Exception e, Boolean needFileInfo)
   at System.Environment.get_StackTrace()
   at CodeFastNewDatabase.Program.Main(String[] args) in f:\Dropbox\Projects\visual studio 2012\Projects\CodeFastNewDatabase\CodeFastNewDatabase\Program.cs:line 32
   at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

以下是异常（外部和内部）的堆栈跟踪

    at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
    at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
    at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
    at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
    at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslateColumnMap(Translator translator, Type elementType, ColumnMap columnMap, MetadataWorkspace workspace, SpanIndex spanIndex, MergeOption mergeOption, Boolean streaming, Boolean valueLayer)
    at System.Data.Entity.Core.Objects.Internal.ObjectQueryExecutionPlanFactory.Prepare(ObjectContext context, DbQueryCommandTree tree, Type elementType, MergeOption mergeOption, Boolean streaming, Span span, IEnumerable`1 compiledQueryParameters, AliasGenerator aliasGenerator)
    at System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
    at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClassb.<GetResults>b__a()
    at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
    at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClassb.<GetResults>b__9()
    at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
    at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
    at System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0()
    at System.Lazy`1.CreateValue()
    at System.Lazy`1.LazyInitValue()
    at System.Lazy`1.get_Value()
    at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()
    at CodeFastNewDatabase.Program.Main(String[] args) in f:\Dropbox\Projects\visual studio 2012\Projects\CodeFastNewDatabase\CodeFastNewDatabase\Program.cs:line 33
    at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
    at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
    at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
    at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
    at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
    at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
    at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
    at System.Threading.ThreadHelper.ThreadStart()

内部异常StackTrace

    at System.Reflection.Emit.TypeBuilder.TermCreateClass(RuntimeModule module, Int32 tk, ObjectHandleOnStack type)
    at System.Reflection.Emit.TypeBuilder.CreateTypeNoLock()
    at System.Reflection.Emit.TypeBuilder.CreateType()
    at System.Data.Entity.Core.Objects.Internal.EntityProxyFactory.ProxyTypeBuilder.CreateType(ModuleBuilder moduleBuilder)
    at System.Data.Entity.Core.Objects.Internal.EntityProxyFactory.BuildType(ModuleBuilder moduleBuilder, ClrEntityType ospaceEntityType, MetadataWorkspace workspace)
    at System.Data.Entity.Core.Objects.Internal.EntityProxyFactory.TryCreateProxyType(EntityType ospaceEntityType, MetadataWorkspace workspace)
    at System.Data.Entity.Core.Objects.Internal.EntityProxyFactory.GetProxyType(ClrEntityType ospaceEntityType, MetadataWorkspace workspace)
    at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.Visit(EntityColumnMap columnMap, TranslatorArg arg)
    at System.Data.Entity.Core.Query.InternalTrees.EntityColumnMap.Accept[TResultType,TArgType](ColumnMapVisitorWithResults`2 visitor, TArgType arg)
    at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.ProcessCollectionColumnMap(CollectionColumnMap columnMap, TranslatorArg arg, ColumnMap discriminatorColumnMap, Object discriminatorValue)
    at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.ProcessCollectionColumnMap(CollectionColumnMap columnMap, TranslatorArg arg)
    at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslatorVisitor.Visit(SimpleCollectionColumnMap columnMap, TranslatorArg arg)
    at System.Data.Entity.Core.Query.InternalTrees.SimpleCollectionColumnMap.Accept[TResultType,TArgType](ColumnMapVisitorWithResults`2 visitor, TArgType arg)
    at System.Data.Entity.Core.Common.Internal.Materialization.Translator.TranslateColumnMap[T](ColumnMap columnMap, MetadataWorkspace workspace, SpanIndex spanIndex, MergeOption mergeOption, Boolean streaming, Boolean valueLayer)

Answer 1

异常消息显示您已使用Blog和Post作为嵌套在Program中的类，而说明说明了这些：

在Program.cs中的Program类定义下面添加以下两个类。

我个人将它们分成不同的文件，但这是另一回事。鉴于他们是公共课程，我仍然对它失败感到惊讶，但听起来这就是问题所在。

至于“函数评估需要所有线程运行” - 这实际上并不是错误，它只是在评估属性需要使用各种线程时显示调试限制。

Answer 2

您链接到的代码将写入目标实体框架5.在实体框架6中，虚拟代理对象使用Lazy<T>的实现进行延迟加载，并且必须以不同的方式处理它才能成为线程安全。我的建议是使用virtual ICollection<Post>而不是virtual List<Post>使用EF6，或者向后退到EF5，您正在引用的教程是针对EF5的。

Answer 3

对我来说，问题是在我的存储库中，我返回IQueryable<T>但忘记了我的服务方法，在返回的结果上使用ToList()方法。

virtual List <t>：“函数评估需要所有线程运行”</t>

3 个答案: