从PowerShell 5迁移至7：无法加载System.ServiceModel.Web v4.0.0.0中的类型

近期从PowerShell 5.1迁移至7.3.6版本，多数脚本运行正常，但有一个调用.NET类的脚本出现异常：无法加载目标类，报错信息如下：

System.Management.Automation.ExtendedTypeSystemException: The following exception occurred while retrieving member "Parse": "Could not load type 'System.ServiceModel.Web.WebInvokeAttribute' from assembly 'System.ServiceModel.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'."
 ---> System.TypeLoadException: Could not load type 'System.ServiceModel.Web.WebInvokeAttribute' from assembly 'System.ServiceModel.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'.
   at System.ModuleHandle.ResolveType(QCallModule module, Int32 typeToken, IntPtr* typeInstArgs, Int32 typeInstCount, IntPtr* methodInstArgs, Int32 methodInstCount, ObjectHandleOnStack type)
   at System.ModuleHandle.ResolveTypeHandle(Int32 typeToken, RuntimeTypeHandle[] typeInstantiationContext, RuntimeTypeHandle[] methodInstantiationContext)
   at System.Reflection.RuntimeModule.ResolveType(Int32 metadataToken, Type[] genericTypeArguments, Type[] genericMethodArguments)
   at System.Reflection.CustomAttribute.FilterCustomAttributeRecord(MetadataToken caCtorToken, MetadataImport& scope, RuntimeModule decoratedModule, MetadataToken decoratedToken, RuntimeType attributeFilterType, Boolean mustBeInheritable, ListBuilder`1& derivedAttributes, RuntimeType& attributeType, IRuntimeMethodInfo& ctorWithParameters, Boolean& isVarArg)
   at System.Reflection.CustomAttribute.AddCustomAttributes(ListBuilder`1& attributes, RuntimeModule decoratedModule, Int32 decoratedMetadataToken, RuntimeType attributeFilterType, Boolean mustBeInheritable, ListBuilder`1 derivedAttributes)
   at System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeModule decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount, RuntimeType attributeFilterType)
   at System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeMethodInfo method, RuntimeType caType, Boolean inherit)
   at System.Management.Automation.DotNetAdapter.MethodCacheEntry.get_IsHidden()
   at System.Management.Automation.DotNetAdapter.GetDotNetMethodImpl[T](Object obj, String methodName, MemberNamePredicate predicate)
   at System.Management.Automation.DotNetAdapter.GetDotNetMethod[T](Object obj, String methodName)
   at System.Management.Automation.Adapter.BaseGetMember[T](Object obj, String memberName)
   --- End of inner exception stack trace ---
   at System.Management.Automation.ExceptionHandlingOps.CheckActionPreference(FunctionContext funcContext, Exception exception)
   at System.Management.Automation.Interpreter.ActionCallInstruction`2.Run(InterpretedFrame frame)
   at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
   at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)

使用Add-Type命令也无法解决该问题，且同一脚本在PowerShell 5.1环境中可正常运行。

问题原因 #

PowerShell 7基于.NET 6+运行时，而System.ServiceModel.Web是.NET Framework专属的程序集，.NET Core/.NET 5+生态中已移除该组件，转而采用ASP.NET Core的现代Web开发组件，这是导致类型加载失败的核心原因。

解决方法 #

1. 安装.NET Framework兼容包（Windows平台适用） #

通过NuGet获取System.ServiceModel.Web的兼容包，手动加载程序集：

# 首次运行安装兼容包，指定CurrentUser范围
Install-Package System.ServiceModel.Web -ProviderName NuGet -Scope CurrentUser

# 定位并加载程序集
$packagePath = (Get-Package System.ServiceModel.Web).Source
Add-Type -Path (Join-Path $packagePath 'lib/net40/System.ServiceModel.Web.dll')

此方法仅适用于Windows系统，无法在跨平台场景下使用。

2. 重构脚本适配.NET 6+标准 #

如果需要跨平台支持，建议重构脚本逻辑：

• 替换WebInvokeAttribute为ASP.NET Core中的[HttpPost]/[HttpGet]等路由特性
• 原WCF REST调用逻辑改用HttpClient或Microsoft.AspNetCore.Mvc相关组件实现
• 序列化/反序列化操作替换为System.Text.Json或Newtonsoft.Json

3. 临时切换至.NET Framework运行时（不推荐长期使用） #

若暂时无法重构脚本，可通过环境变量强制PowerShell 7使用.NET Framework运行：

$env:DOTNET_ROLL_FORWARD_3=0
pwsh -UseWindowsPowerShell

该方式本质上是调用PowerShell 5.1的运行环境，无法利用PowerShell 7的新特性。

内容的提问来源于stack exchange，提问作者Vadim Berman