Tho*_*hou 15 c# entity-framework asp.net-core
当我尝试跑步时
dotnet ef migration add Init
我得到错误
无法创建类型为“IdentityContext”的对象。
我知道是什么导致了这个问题。我想学习使用消息总线并将其添加到我的项目中，所以我参加了一些课程并实施了它。Ofc 总线工作正常。但问题是我无法再通过 EF 进行迁移。
我之前的 Startup.cs 是。
public class Program
{
public static void Main(string[] args)
{
CreateWebHostBuilder(args).Build().Run();
}
public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>();
}
现在看起来像这样。
public static void Main(string[] args)
{
ServiceHost.Create<Startup>(args)
.UseRabbitMq()
.Build()
.Run();
}
和 ServiceHost 类
public void Run() => _webHost.Run();
public static HostBuilder Create<TStartup>(string[] args) where TStartup : class
{
Console.Title = typeof(TStartup).Namespace;
var config = new ConfigurationBuilder()
.AddEnvironmentVariables()
.AddCommandLine(args)
.Build();
var webHostBuilder = WebHost.CreateDefaultBuilder()
.UseConfiguration(config)
.UseStartup<TStartup>();
return new HostBuilder(webHostBuilder.Build());
}
所以有人会建议为什么迁移停止工作？对我来说，它看起来应该有效，但事实并非如此，我想我错了。
而且我在 Startup.cs 中有
services.AddEntityFrameworkNpgsql().AddDbContext<IdentityContext>(options =>
options.UseNpgsql(Configuration.GetConnectionString("IdentityConnection")));
编辑 IdentityContext 类：
public class IdentityContext : DbContext
{
public IdentityContext(DbContextOptions<IdentityContext> options) : base(options)
{
while (!Debugger.IsAttached)
{
Thread.Sleep(100);
}
}
public DbSet<User> Users { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<User>().HasIndex(user => user.Email).IsUnique();
modelBuilder.Entity<User>().HasIndex(user => user.Username).IsUnique();
}
}
编辑2。详细迁移
Using project '/home/msek/Projects/inz/CrossX/src/CrossX.Identity/CrossX.Identity.csproj'.
Using startup project '/home/msek/Projects/inz/CrossX/src/CrossX.Identity/CrossX.Identity.csproj'.
Writing '/home/msek/Projects/inz/CrossX/src/CrossX.Identity/obj/CrossX.Identity.csproj.EntityFrameworkCore.targets'...
dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=/tmp/tmpCq3PQa.tmp /verbosity:quiet /nologo /home/msek/Projects/inz/CrossX/src/CrossX.Identity/CrossX.Identity.csproj
Writing '/home/msek/Projects/inz/CrossX/src/CrossX.Identity/obj/CrossX.Identity.csproj.EntityFrameworkCore.targets'...
dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=/tmp/tmpR48yu8.tmp /verbosity:quiet /nologo /home/msek/Projects/inz/CrossX/src/CrossX.Identity/CrossX.Identity.csproj
dotnet build /home/msek/Projects/inz/CrossX/src/CrossX.Identity/CrossX.Identity.csproj /verbosity:quiet /nologo
Build succeeded.
0 Warning(s)
0 Error(s)
Time Elapsed 00:00:01.17
dotnet exec --depsfile /home/msek/Projects/inz/CrossX/src/CrossX.Identity/bin/Debug/netcoreapp2.2/CrossX.Identity.deps.json --additionalprobingpath /home/msek/.nuget/packages --runtimeconfig /home/msek/Projects/inz/CrossX/src/CrossX.Identity/bin/Debug/netcoreapp2.2/CrossX.Identity.runtimeconfig.json /home/msek/.dotnet/tools/.store/dotnet-ef/2.2.2/dotnet-ef/2.2.2/tools/netcoreapp2.2/any/tools/netcoreapp2.0/any/ef.dll migrations add Init --assembly /home/msek/Projects/inz/CrossX/src/CrossX.Identity/bin/Debug/netcoreapp2.2/CrossX.Identity.dll --startup-assembly /home/msek/Projects/inz/CrossX/src/CrossX.Identity/bin/Debug/netcoreapp2.2/CrossX.Identity.dll --project-dir /home/msek/Projects/inz/CrossX/src/CrossX.Identity/ --language C# --working-dir /home/msek/Projects/inz/CrossX/src/CrossX.Identity --verbose --root-namespace CrossX.Identity
Using assembly 'CrossX.Identity'.
Using startup assembly 'CrossX.Identity'.
Using application base '/home/msek/Projects/inz/CrossX/src/CrossX.Identity/bin/Debug/netcoreapp2.2'.
Using working directory '/home/msek/Projects/inz/CrossX/src/CrossX.Identity'.
Using root namespace 'CrossX.Identity'.
Using project directory '/home/msek/Projects/inz/CrossX/src/CrossX.Identity/'.
Finding DbContext classes...
Finding IDesignTimeDbContextFactory implementations...
Finding application service provider...
Finding IWebHost accessor...
No CreateWebHostBuilder(string[]) method was found on type 'CrossX.Identity.Program'.
No application service provider was found.
Finding DbContext classes in the project...
Found DbContext 'IdentityContext'.
Microsoft.EntityFrameworkCore.Design.OperationException: Unable to create an object of type 'IdentityContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728 ---> System.MissingMethodException: No parameterless constructor defined for this object.
at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean wrapExceptions, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor)
at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean wrapExceptions, Boolean skipCheckThis, Boolean fillCache)
at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass12_3.<FindContextTypes>b__13()
--- End of inner exception stack trace ---
at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.<>c__DisplayClass12_3.<FindContextTypes>b__13()
at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func`1 factory)
at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(String contextType)
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.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
Unable to create an object of type 'IdentityContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728
小智 92
如果您使用的是 CLI，
当您的解决方案包含 2 个项目 API/WebApp 和一个 DataAcess 项目时，您可以在命令行中传递选项。
My_Solution
|DataAccess_Project
|-- DbContext.cs
|WebApp_Project
|-- Startup.cs
切换到解决方案目录
CD My_Solution
dotnet ef migrations add InitialCreate --project DataAccess_Project --startup-project WebApp_Project
dotnet ef database update --project DataAccess_Project --startup-project WebApp_Project
C. *_*iel 14
我的问题是我没有将解决方案中的 api 项目设置为 Startup Project，因此它找不到任何 Startup.cs 或类似的东西。
如果您使用新的 .NET 5 顶级代码功能，那么这肯定是迁移失败的原因。在类中使用顶级语句Program会使 EF 工具无法访问它，因为它既不包含命名空间也不包含类名。
顶层声明：
Console.WriteLine("Hello, World!");
经典Program班：
namespace MyApp
{
public class Program
{
public static void Main(string[] args)
{
Console.WriteLine("Hello, World!");
}
}
}
如果是这样的话，那就回到经典模式吧。
似乎您实现了 IdentityContext，但在您的应用程序中的某处仍在尝试引用 DbContext。确保 Identitycontext 正在扩展 DbContext。
https://docs.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext
编辑：如https://docs.microsoft.com/en-gb/ef/core/miscellaneous/cli/dbcontext-creation 中所述实现了 IDesignTimeDbContextFactory
小智 6
在 Program 类中创建一个名为CreateWebHostBuilder的方法。将主方法主体移至该类并从 Main 方法调用该类。新的实施将是：
public static void Main(string[] args)
{
CreateWebHostBuilder(args).Build().Run();
}
public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
ServiceHost.Create<Startup>(args)
.UseRabbitMq()
.Build()
.Run();
ef 工具会查找 CreateWebHostBuilder 方法并在找不到任何方法时返回错误。
改进尖叫的答案
我有一个如下所示的项目结构
解决方案
我的迁移位于 X.Repository 下，我的启动项目是 X.Api。正确设置所有内容后，没有任何代码错误，我无法使用以下命令运行迁移
dotnet ef migrations add CreateABCTable
应用尖叫建议的解决方案，我可以运行我的迁移。我使用了下面的命令
dotnet ef migrations add CreateABCTable --project X.Repository.csproj --startup-project ../X.Api/X.Api.csproj