为什么 EF Scaffold-DbContext 命令在报告“未找到设计时服务”后抛出 NRE，当面向 net6.0 时？

Question

我目前使用的是最新的 net6.0 预览版： dotnet-sdk-6.0.100-preview.7.21379.14-win-x64

我必须重新定位到 net5.0 并回滚到使用其关联的包才能使 Scaffold-DbContext 工作。

完整的 EF 命令如下：

Scaffold-DbContext Name=<connection-string-name> Microsoft.EntityFrameworkCore.SqlServer -Context MyDbContext -OutputDir ModelsNew -NoPluralize -Force -Verbose 

这是最后的消息，然后是 NRE 的堆栈跟踪：

No design-time services were found.
System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.EntityFrameworkCore.Storage.Internal.NamedConnectionStringResolver.get_ApplicationServiceProvider() in Microsoft.EntityFrameworkCore.Relational.dll:token 0x6000638+0x0
   at Microsoft.EntityFrameworkCore.Storage.Internal.NamedConnectionStringResolverBase.ResolveConnectionString(String connectionString) in Microsoft.EntityFrameworkCore.Relational.dll:token 0x600063a+0xc
   at Microsoft.EntityFrameworkCore.Scaffolding.Internal.ReverseEngineerScaffolder.ScaffoldModel(String connectionString, DatabaseModelFactoryOptions databaseOptions, ModelReverseEngineerOptions modelOptions, ModelCodeGenerationOptions codeOptions) in Microsoft.EntityFrameworkCore.Design.dll:token 0x600023d+0x79
   at Microsoft.EntityFrameworkCore.Design.Internal.DatabaseOperations.ScaffoldContext(String provider, String connectionString, String outputDir, String outputContextDir, String dbContextClassName, IEnumerable`1 schemas, IEnumerable`1 tables, String modelNamespace, String contextNamespace, Boolean useDataAnnotations, Boolean overwriteFiles, Boolean useDatabaseNames, Boolean suppressOnConfiguring, Boolean noPluralize) in Microsoft.EntityFrameworkCore.Design.dll:token 0x600043e+0x11c
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.ScaffoldContextImpl(String provider, String connectionString, String outputDir, String outputDbContextDir, String dbContextClassName, IEnumerable`1 schemaFilters, IEnumerable`1 tableFilters, String modelNamespace, String contextNamespace, Boolean useDataAnnotations, Boolean overwriteFiles, Boolean useDatabaseNames, Boolean suppressOnConfiguring, Boolean noPluarlize) in Microsoft.EntityFrameworkCore.Design.dll:token 0x60003ed+0x32
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.ScaffoldContext.<>c__DisplayClass0_0.<.ctor>b__0() in Microsoft.EntityFrameworkCore.Design.dll:token 0x60006ed+0x0
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0() in Microsoft.EntityFrameworkCore.Design.dll:token 0x60006f3+0x0
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action) in Microsoft.EntityFrameworkCore.Design.dll:token 0x600066a+0xc
Object reference not set to an instance of an object.

项目均指定LangVersion预览

升级到版本 6.0.100-rc.1.21458.32 、.NET 6.0.0-rc.1 候选版本和 dotnet-ef版本 6.0.0-rc.1.21452.10后，此 Scaffold-DbContext 崩溃仍然存在工具。

Answer 1

解决方法是简单地用显式连接字符串替换命名连接字符串。 执行此操作时，将报告以下警告：

To protect potentially sensitive information in your connection string, you should move it out of source code. You can avoid scaffolding the connection string by using the Name= syntax to read it from configuration - see https://go.microsoft.com/fwlink/?linkid=2131148. For more guidance on storing connection strings, see http://go.microsoft.com/fwlink/?LinkId=723263.

Scaffold-DbContext 命令似乎已经完成了它的工作； 但是尽管包含了 -Verbose 开关，但 NuGet PMC 窗口中没有出现任何输出。

Answer 2

此问题已在 VS 2022 版本 17.1.0 预览版 1.1 的正式版本中得到解决。

EF Scaffold-DbContext 命令现在可以使用命名连接字符串成功完成，同时面向 net6.0。

即使在发布候选版本期间，这也被打破了； 但在最后一次发射时被及时修复。