[英]virtual List<T> :“The function evaluation requires all threads to run”
我正在按照以下教程快速学习代码。 代码优先到新数据库
我已经完成了本教程的第4步:当我尝试运行我的代码时出现问题。 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."}
有一个内在的例外
{"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db中创建数据库并插入值。
如果我删除类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。
[堆栈跟踪]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()
这是异常(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)
异常消息显示您已将Blog
和Post
用作嵌套在Program
类,而说明指出:
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” - 这实际上并不是一个错误 ,它只是在评估属性需要使用各种线程时显示调试的限制。
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>
实现进行延迟加载,并且必须以不同方式处理它才能保证线程安全。 我的建议是使用virtual ICollection<Post>
而不是使用EF6的virtual List<Post>
,或者向后退到EF5,您正在引用的教程是针对EF5设计的。
我的问题是,在我的Repository中,我返回了一个IQueryable<T>
但忘记了我的Service方法,对返回的结果使用ToList()
方法。
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