对于MySQL DB，Pomelo Entity Framework核心脚手架失败“无法添加注释，因为已经存在具有相同名称的注释”

问题描述

当我尝试使用以下方法来搭建现有的MysqL数据库时：

Scaffold-DbContext“ server = server; user = user; password = pw; database = db”“ Pomelo.EntityFrameworkCore.MysqL” -OutputDir EF -f

我收到以下错误：

system.invalidOperationException: The annotation 'MysqL:IndexPrefixLength' cannot be added because an annotation with the same name already exists**.
   at Microsoft.EntityFrameworkCore.Infrastructure.Annotatable.AddAnnotation(String name,Annotation annotation)
   at Microsoft.EntityFrameworkCore.Infrastructure.Annotatable.AddAnnotation(String name,Object value)
   at Microsoft.EntityFrameworkCore.Infrastructure.Annotatable.Microsoft.EntityFrameworkCore.Metadata.IMutableAnnotatable.AddAnnotation(String name,Object value)
   at Microsoft.EntityFrameworkCore.MutableAnnotatableExtensions.AddAnnotations(IMutableAnnotatable annotatable,IEnumerable`1 annotations)
   at Microsoft.EntityFrameworkCore.Scaffolding.Internal.RelationalScaffoldingModelFactory.VisitIndex(EntityTypeBuilder builder,DatabaseIndex index)
   at Microsoft.EntityFrameworkCore.Scaffolding.Internal.RelationalScaffoldingModelFactory.VisitIndexes(EntityTypeBuilder builder,ICollection`1 indexes)
   at Microsoft.EntityFrameworkCore.Scaffolding.Internal.RelationalScaffoldingModelFactory.VisitTable(ModelBuilder modelBuilder,DatabaseTable table)
   at Microsoft.EntityFrameworkCore.Scaffolding.Internal.RelationalScaffoldingModelFactory.VisitTables(ModelBuilder modelBuilder,ICollection`1 tables)
   at Microsoft.EntityFrameworkCore.Scaffolding.Internal.RelationalScaffoldingModelFactory.VisitDatabaseModel(ModelBuilder modelBuilder,DatabaseModel databaseModel)
   at Microsoft.EntityFrameworkCore.Scaffolding.Internal.RelationalScaffoldingModelFactory.Create(DatabaseModel databaseModel,Boolean useDatabaseNames)
   at Microsoft.EntityFrameworkCore.Scaffolding.Internal.ReverseEngineerScaffolder.ScaffoldModel(String connectionString,DatabaseModelFactoryOptions databaSEOptions,ModelReverseEngineerOptions modelOptions,ModelCodeGenerationoptions codeOptions)
   at Microsoft.EntityFrameworkCore.Design.Internal.DatabaSEOperations.ScaffoldContext(String provider,String connectionString,String outputDir,String outputContextDir,String dbContextClassName,IEnumerable`1 schemas,IEnumerable`1 tables,Boolean useDataAnnotations,Boolean overwriteFiles,Boolean useDatabaseNames)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.ScaffoldContextImpl(String provider,String outputDbContextDir,IEnumerable`1 schemaFilters,IEnumerable`1 tableFilters,Boolean useDatabaseNames)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.ScaffoldContext.<>c__displayClass0_0.<.ctor>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__displayClass3_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
The annotation 'MysqL:IndexPrefixLength' cannot be added because an annotation with the same name already exists.*

我已经成功地使用Microsoft软件包在同一项目中为同一数据库安装了脚手架。

解决方法

Pomelo团队已确认此问题是错误。 如果一列上有多个索引并且两个索引都使用索引前缀，则会发生此异常。修复程序将很快发布：

https://github.com/PomeloFoundation/Pomelo.EntityFrameworkCore.MySql/issues/1189