EFCore2.1项目添加-迁移NullReferenceException

Question

最近，我在一个转换为DotNetCore2.1的项目上获得了一个NullReferenceException。

我的EF库项目是dotnet核心2.1。代码优先迁移。

CsvHelper 6.0.2
Microsoft.EntityFrameworkCore 2.1.0
Microsoft.EntityFrameworkCore.Design 2.1.0
Microsoft.EntityFrameworkCore.SqlServer 2.1.0
Microsoft.EntityFrameworkCore.Tools 2.1.0

从“添加迁移”命令输出。

PM> add-migration -Name MyMigration -Context EscData01Context -Project Data\EscData01 -StartupProject PacmsTri -verbose
Using project 'Data\EscData01'.
Using startup project 'PacmsTri'.
Build started...
Build succeeded.
C:\Program Files\dotnet\dotnet.exe exec --depsfile C:\temp\PacmsTri\dev\***\source\PacmsTri\bin\Debug\netcoreapp2.1\PacmsTri.deps.json --additionalprobingpath "C:\Users\***\.nuget\packages" --additionalprobingpath "C:\Program Files\dotnet\sdk\NuGetFallbackFolder" --runtimeconfig C:\temp\PacmsTri\dev\***\source\PacmsTri\bin\Debug\netcoreapp2.1\PacmsTri.runtimeconfig.json "C:\Users\***\.nuget\packages\microsoft.entityframeworkcore.tools\2.1.0\tools\netcoreapp2.0\any\ef.dll" migrations add MyMigration --json --context EscData01Context --verbose --no-color --prefix-output --assembly C:\temp\PacmsTri\dev\****\source\PacmsTri\bin\Debug\netcoreapp2.1\EscData01.dll --startup-assembly C:\temp\PacmsTri\dev\****\source\PacmsTri\bin\Debug\netcoreapp2.1\PacmsTri.dll --project-dir C:\temp\PacmsTri\dev\****\source\Data\EscData01\ --language C# --working-dir C:\temp\PacmsTri\dev\****\source --root-namespace Sms.Office.Data.EscData01
Using assembly 'EscData01'.
Using startup assembly 'PacmsTri'.
Using application base 'C:\temp\PacmsTri\dev\***\source\PacmsTri\bin\Debug\netcoreapp2.1'.
Using working directory 'C:\temp\PacmsTri\dev\***\source\PacmsTri'.
Using root namespace 'Sms.Office.Data.EscData01'.
Using project directory 'C:\temp\PacmsTri\dev\***\source\Data\EscData01\'.
Finding DbContext classes...
Finding IDesignTimeDbContextFactory implementations...
Finding application service provider...
Finding IWebHost accessor...
Using environment 'Development'.
Using application service provider from IWebHost accessor on 'Program'.
Found DbContext 'AuthDbContext'.
Found DbContext 'DmsContext'.
Found DbContext 'EscData01Context'.
Found DbContext 'MailServicesContext'.
Found DbContext 'PmsDdContext'.
Finding DbContext classes in the project...
Using context 'EscData01Context'.
Microsoft.EntityFrameworkCore.Infrastructure[10403]
      Entity Framework Core 2.1.0-rtm-30799 initialized 'EscData01Context' using provider 'Microsoft.EntityFrameworkCore.SqlServer' with options: None
Finding design-time services for provider 'Microsoft.EntityFrameworkCore.SqlServer'...
Using design-time services from provider 'Microsoft.EntityFrameworkCore.SqlServer'.
Finding design-time services referenced by assembly 'PacmsTri'.
No referenced design-time services were found.
Finding IDesignTimeServices implementations in assembly 'PacmsTri'...
No design-time services were found.
System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.EntityFrameworkCore.Metadata.Internal.TableMapping.<>c.<GetRootType>b__10_0(IEntityType t)
   at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source, Func`2 predicate)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.TableMapping.GetRootType()
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.GetSortedProperties(TableMapping target)
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.Add(TableMapping target, DiffContext diffContext)+MoveNext()
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.DiffCollection[T](IEnumerable`1 sources, IEnumerable`1 targets, DiffContext diffContext, Func`4 diff, Func`3 add, Func`3 remove, Func`4[] predicates)+MoveNext()
   at System.Linq.Enumerable.ConcatIterator`1.MoveNext()
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.Sort(IEnumerable`1 operations, DiffContext diffContext)
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.GetDifferences(IModel source, IModel target)
   at Microsoft.EntityFrameworkCore.Migrations.Design.MigrationsScaffolder.ScaffoldMigration(String migrationName, String rootNamespace, String subNamespace, String language)
   at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigration.<>c__DisplayClass0_1.<.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)
Object reference not set to an instance of an object.
PM> 

我尝试在我的启动项目中添加一个IDesignTimeServices对象，并尝试添加一个IDesignTimeDbContextFactory。我还尝试创建一个具有相同dotnet和EF版本编号的新示例项目，指向相同的db，并能够生成上下文并成功地创建迁移。所以我看不出这两个项目之间一定有什么不同。

PM> add-migration MyMigration2 -Project ClassLibrary1 -StartupProject WebApplication20 -Context ESC_DATA01Context
Microsoft.EntityFrameworkCore.Infrastructure[10403]
      Entity Framework Core 2.1.0-rtm-30799 initialized 'ESC_DATA01Context' using provider 'Microsoft.EntityFrameworkCore.SqlServer' with options: None
To undo this action, use Remove-Migration.

任何帮助都非常感谢。

更新：

我最初贴出了这个错误是由将项目迁移到标准2.0引起的，但是在将它转换回dotnetcore2.1之后，这个想法被折扣了，并且错误持续存在。

Answer 1

看起来，这个错误是由于对我的ModelSnapshot类中的模型的引用导致的，这些模型已经不存在了。包括一些在我将AspNetCore.Identity从上下文中删除后遗留下来的身份模型。

从我的EscData01ContextModelSnapshot中删除下面的代码修复了这个问题。

modelBuilder.Entity("Sms.Office.Data.EscData01.Models.ExcelTemplate", b =>
{
    b.HasOne("Sms.Office.Data.EscData01.Models.File", "File")
        .WithMany()
        .HasForeignKey("FileId")
        .OnDelete(DeleteBehavior.Cascade);
});
modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityRoleClaim<string>", b =>
{
    b.HasOne("Sms.Office.Data.EscData01.Authentication.ApplicationRole")
        .WithMany()
        .HasForeignKey("RoleId")
        .OnDelete(DeleteBehavior.Cascade);
});
modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserClaim<string>", b =>
{
     b.HasOne("Sms.Office.Data.EscData01.Authentication.ApplicationUser")
         .WithMany()
         .HasForeignKey("UserId")
         .OnDelete(DeleteBehavior.Cascade);
});
modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserLogin<string>", b =>
{
     b.HasOne("Sms.Office.Data.EscData01.Authentication.ApplicationUser")
         .WithMany()
         .HasForeignKey("UserId")
         .OnDelete(DeleteBehavior.Cascade);
});
modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserRole<string>", b =>
{
     b.HasOne("Sms.Office.Data.EscData01.Authentication.ApplicationRole")
         .WithMany()
         .HasForeignKey("RoleId")
         .OnDelete(DeleteBehavior.Cascade);
     b.HasOne("Sms.Office.Data.EscData01.Authentication.ApplicationUser")
         .WithMany()
         .HasForeignKey("UserId")
         .OnDelete(DeleteBehavior.Cascade);
});   
modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityUserToken<string>", b =>
{
     b.HasOne("Sms.Office.Data.EscData01.Authentication.ApplicationUser")
         .WithMany()
         .HasForeignKey("UserId")
         .OnDelete(DeleteBehavior.Cascade);
});