第一次迁移时访问Microsoft.Extensions.Hosting服务时发生错误 [英] An error occurred while accessing the Microsoft.Extensions.Hosting services when do first migrations
本文介绍了第一次迁移时访问Microsoft.Extensions.Hosting服务时发生错误的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我不明白什么地方错了。
i尝试在.net核心mvc中使用简单的模型制作简单的简单模型，其中只有很少的字段
I dont understand what wrong. i try make simple simple crud in .net core mvc with a very simple model wich have few fields
这是我的模型
public class Employee
{
[Key] public int EmployeeId { get; set; }
[Required] public string FistName { get; set; }
[Required] public string LastName { get; set; }
public int PositionId { get; set; }
public virtual Position Position { get; set; }
}
public class Position
{
[Key]
public int PositionId { get; set; }
public string PositionName { get; set; }
public ICollection<Employee> Employees { get; set; }
}
然后我创建应用上下文
public class EmployeeContext : DbContext
{
public EmployeeContext(DbContextOptions<EmployeeContext> options)
: base(options)
{
}
public DbSet<Employee> Employees { get; set; }
public DbSet<Position> Positions { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Employee>()
.HasOne(e => e.Position)
.WithMany()
.HasForeignKey(e => e.PositionId);
}
}
并在Startup.cs中注册上下文
and register context in Startup.cs
public void ConfigureServices(IServiceCollection services)
{
services.Configure<CookiePolicyOptions>(options =>
{
// This lambda determines whether user consent for non-essential cookies is needed for a given request.
options.CheckConsentNeeded = context => true;
options.MinimumSameSitePolicy = SameSiteMode.None;
});
services.AddDbContext<EmployeeContext>(item =>item.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
}
可能还需要一个.csproj和program.cs文件代码
may be need one more file code of .csproj and program.cs
<Project Sdk="Microsoft.NET.Sdk.Web">
<PropertyGroup>
<TargetFramework>net461</TargetFramework>
<DebugType>full</DebugType>
</PropertyGroup>
<ItemGroup>
<PackageReference Include="Microsoft.AspNetCore" Version="2.2.0" />
<PackageReference Include="Microsoft.AspNetCore.CookiePolicy" Version="2.2.8" />
<PackageReference Include="Microsoft.AspNetCore.Mvc" Version="2.2.0" />
<PackageReference Include="Microsoft.AspNetCore.StaticFiles" Version="2.2.0" />
<PackageReference Include="Microsoft.EntityFrameworkCore" Version="3.1.2" />
<PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="3.1.2">
<PrivateAssets>all</PrivateAssets>
<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
</PackageReference>
<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="3.1.2" />
<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer.Design" Version="1.1.6" />
<PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="3.1.2">
<PrivateAssets>all</PrivateAssets>
<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
</PackageReference>
<PackageReference Include="Microsoft.Extensions.Logging.Configuration" Version="3.1.2" />
<PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="3.1.1" />
</ItemGroup>
</Project>
public class Program
{
public static void Main(string[] args)
{
CreateWebHostBuilder(args).Build().Run();
}
public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>();
}
然后我尝试先进行迁移，但是我看到一个非常奇怪的错误
Add-Migration FirstInit -verbose
then i try do first migrate, but I see a very strange error Add-Migration FirstInit -verbose
Using project 'Crud'.
Using startup project 'Crud'.
Build started...
Build succeeded.
C:\.nuget\packages\microsoft.entityframeworkcore.tools\3.1.2\tools\net461\win-x86\ef.exe migrations add FirstInit --json --verbose --no-color --prefix-output --assembly C:\source\repos\Crud\Crud\bin\Debug\net461\Crud.exe --startup-assembly C:\source\repos\Crud\Crud\bin\Debug\net461\Crud.exe --project-dir C:\source\repos\Crud\Crud\ --language C# --working-dir C:\source\repos\Crud --root-namespace Crud
Using assembly 'Crud'.
Using startup assembly 'Crud'.
Using application base 'C:\source\repos\Crud\Crud\bin\Debug\net461'.
Using working directory 'C:\source\repos\Crud\Crud'.
Using root namespace 'Crud'.
Using project directory 'C:\source\repos\Crud\Crud\'.
Using configuration file 'C:\source\repos\Crud\Crud\bin\Debug\net461\Crud.exe.config'.
Using assembly 'Crud'.
Using startup assembly 'Crud'.
Using application base 'C:\source\repos\Crud\Crud\bin\Debug\net461'.
Using working directory 'C:\source\repos\Crud\Crud'.
Using root namespace 'Crud'.
Using project directory 'C:\source\repos\Crud\Crud\'.
Finding DbContext classes...
Finding IDesignTimeDbContextFactory implementations...
Finding application service provider...
Finding Microsoft.Extensions.Hosting service provider...
Using environment 'Development'.
System.TypeLoadException: There is no implementation of the GetItem method in the type "Microsoft.AspNetCore.Mvc.Razor.Internal.FileProviderRazorProjectFileSystem" from assembly "Microsoft.AspNetCore.Mvc.Razor, Version=2.2.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60".
в Microsoft.Extensions.DependencyInjection.MvcRazorMvcCoreBuilderExtensions.AddRazorViewEngineServices(IServiceCollection services)
в Microsoft.Extensions.DependencyInjection.MvcRazorMvcCoreBuilderExtensions.AddRazorViewEngine(IMvcCoreBuilder builder)
в Microsoft.Extensions.DependencyInjection.MvcServiceCollectionExtensions.AddMvc(IServiceCollection services)
в Crud.Startup.ConfigureServices(IServiceCollection services) в C:\source\repos\Crud\Crud\Startup.cs:строка 38
--- End the stack trace from the previous location where the exception occurred ---
в System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
в Microsoft.AspNetCore.Hosting.ConventionBasedStartup.ConfigureServices(IServiceCollection services)
в Microsoft.AspNetCore.Hosting.Internal.WebHost.EnsureApplicationServices()
в Microsoft.AspNetCore.Hosting.Internal.WebHost.Initialize()
в Microsoft.AspNetCore.Hosting.WebHostBuilder.Build()
An error occurred while accessing the Microsoft.Extensions.Hosting services. Continuing without the application service provider. Error: There is no implementation of the GetItem method in the type "Microsoft.AspNetCore.Mvc.Razor.Internal.FileProviderRazorProjectFileSystem" from assembly "Microsoft.AspNetCore.Mvc.Razor, Version=2.2.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60".
No application service provider was found.
Finding DbContext classes in the project...
Found DbContext 'EmployeeContext'.
Microsoft.EntityFrameworkCore.Design.OperationException: Unable to create an object of type 'EmployeeContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728 ---> System.MissingMethodException:There are no parameterless constructors defined for this object..
в System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck)
в System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)
в System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)
в System.Activator.CreateInstance(Type type, Boolean nonPublic)
в System.Activator.CreateInstance(Type type)
в Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass13_3.<FindContextTypes>b__13()
--- End trace of internal exception stack ---
в Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass13_3.<FindContextTypes>b__13()
в Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func`1 factory)
в Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(String contextType)
в Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)
в Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType)
в Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigration.<>c__DisplayClass0_0.<.ctor>b__0()
в Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
в Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
Unable to create an object of type 'EmployeeContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728
这三行有什么问题？
推荐答案
EF调用CreateWebHostBuilder或BuildWebHost而不运行Main。因此，Iconfiguration为空。
EF calls CreateWebHostBuilder or BuildWebHost without running Main. So Iconfiguration is null.
创建新的 IDesignTimeDbContextFactory 类。
public class EmployeeContext : DbContext
{
//Dbcontext implementation
}
public class EmployeeFactory : IDesignTimeDbContextFactory<EmployeeContext>
{
public EmployeeContext CreateDbContext(string[] args)
{
var optionsBuilder = new DbContextOptionsBuilder<EmployeeContext>();
optionsBuilder.UseSqlServer("your connection string");
return new EmployeeContext(optionsBuilder.Options);
}
}
您正在使用新的.net核心EF，同时使用IHostBuilder （在像您这样的旧版本中，提供程序是IWebHostBuilder）。这些工具首先尝试通过调用Program.CreateHostBuilder（），调用Build（），然后访问Services属性来获取服务提供商。
You are using new .net core EF wich use IHostBuilder.(in an older version like yours the provider is IWebHostBuilder). The tools first try to obtain the service provider by invoking the Program.CreateHostBuilder(), calling Build(), then accessing the Services property.
EF需要构建模型并在不启动应用程序的情况下使用DbContext。 EF调用方法时，您的配置服务仍为null，这就是为什么您会收到错误消息。
EF needs to build the model and use the DbContext without starting the application. When EF invokes methods, your config services are still null that's why you get an error.
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