在程序集 EF6 中找不到上下文类型

Question

我正在做一个基于 nopCommerce 的项目。为了更新自定义实体，我想启用 EF 迁移。所以我运行以下命令：

Enable-Migrations -StartUpProjectName nop.web -ContextProjectName Nop.Plugin.Payments.Deposit -verbose

并得到错误：

Using StartUp project 'Nop.Web'.
System.Data.Entity.Migrations.Infrastructure.MigrationsException: No context type was found in the assembly 'Nop.Plugin.Payments.Deposit'.
   at System.Data.Entity.Utilities.TypeFinder.FindType(Type baseType, String typeName, Func`2 filter, Func`2 noType, Func`3 multipleTypes, Func`3 noTypeWithName, Func`3 multipleTypesWithName)
   at System.Data.Entity.Migrations.Design.ToolingFacade.GetContextTypeRunner.Run()
   at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate)
   at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate)
   at System.Data.Entity.Migrations.Design.ToolingFacade.Run(BaseRunner runner)
   at System.Data.Entity.Migrations.Design.ToolingFacade.GetContextType(String contextTypeName)
   at System.Data.Entity.Migrations.EnableMigrationsCommand.FindContextToEnable(String contextTypeName)
   at System.Data.Entity.Migrations.EnableMigrationsCommand.<>c__DisplayClass2.<.ctor>b__0()
   at System.Data.Entity.Migrations.MigrationsDomainCommand.Execute(Action command)
No context type was found in the assembly 'Nop.Plugin.Payments.Deposit'.

上下文 class 定义如下：

public class DepositTransactionObjectContext : DbContext, IDbContext
{
    public DepositTransactionObjectContext(string nameOrConnectionString) : base(nameOrConnectionString) { }

    public DepositTransactionObjectContext() { }

    public IList<TEntity> ExecuteStoredProcedureList<TEntity>(string commandText, params object[] parameters) where TEntity : BaseEntity, new()
    {
        throw new System.NotImplementedException();
    }

    public IEnumerable<TElement> SqlQuery<TElement>(string sql, params object[] parameters)
    {
        throw new System.NotImplementedException();
    }

    public int ExecuteSqlCommand(string sql, bool doNotEnsureTransaction = false, int? timeout = null, params object[] parameters)
    {
        throw new System.NotImplementedException();
    }

    public void Detach(object entity)
    {
        throw new System.NotImplementedException();
    }

    public bool ProxyCreationEnabled { get; set; }
    public bool AutoDetectChangesEnabled { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Configurations.Add(new DepositTransactionMap());

        base.OnModelCreating(modelBuilder);
    }

    public string CreateDatabaseInstallationScript()
    {
        return ((IObjectContextAdapter)this).ObjectContext.CreateDatabaseScript();
    }

    public void Install()
    {
        //It's required to set initializer to null (for SQL Server Compact).
        //otherwise, you'll get something like "The model backing the 'your context name' context has changed since the database was created. Consider using Code First Migrations to update the database"
        Database.SetInitializer<DepositTransactionObjectContext>(null);

        Database.ExecuteSqlCommand(CreateDatabaseInstallationScript());
        SaveChanges();
    }

    public void Uninstall()
    {
        this.DropPluginTable("DepositTransaction");
    }

    public new IDbSet<TEntity> Set<TEntity>() where TEntity : BaseEntity
    {
        return base.Set<TEntity>();
    }
}

我创建了空项目并在那里启用了迁移。然后我复制并调整了 Configuration.cs 使其看起来像这样：

namespace Nop.Plugin.Payments.Deposit.Migrations
{
    using Data;
    using System.Data.Entity.Migrations;

    internal sealed class Configuration : DbMigrationsConfiguration<DepositTransactionObjectContext>
    {
        public Configuration()
        {
            AutomaticMigrationsEnabled = true;
        }

        protected override void Seed(DepositTransactionObjectContext context)
        {
        }
    }
}

然而，当我运行添加迁移时，出现以下错误：

Using StartUp project 'Nop.Web'.
Using NuGet project 'Nop.Plugin.Payments.Deposit'.
System.Data.Entity.Migrations.Infrastructure.MigrationsException: No migrations configuration type was found in the assembly 'Nop.Plugin.Payments.Deposit'. (In Visual Studio you can use the Enable-Migrations command from Package Manager Console to add a migrations configuration).
   at System.Data.Entity.Utilities.TypeFinder.FindType(Type baseType, String typeName, Func`2 filter, Func`2 noType, Func`3 multipleTypes, Func`3 noTypeWithName, Func`3 multipleTypesWithName)
   at System.Data.Entity.Migrations.Utilities.MigrationsConfigurationFinder.FindMigrationsConfiguration(Type contextType, String configurationTypeName, Func`2 noType, Func`3 multipleTypes, Func`3 noTypeWithName, Func`3 multipleTypesWithName)
   at System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.FindConfiguration()
   at System.Data.Entity.Migrations.Design.ToolingFacade.ScaffoldRunner.Run()
   at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate)
   at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate)
   at System.Data.Entity.Migrations.Design.ToolingFacade.Run(BaseRunner runner)
   at System.Data.Entity.Migrations.Design.ToolingFacade.Scaffold(String migrationName, String language, String rootNamespace, Boolean ignoreChanges)
   at System.Data.Entity.Migrations.AddMigrationCommand.Execute(String name, Boolean force, Boolean ignoreChanges)
   at System.Data.Entity.Migrations.AddMigrationCommand.<>c__DisplayClass2.<.ctor>b__0()
   at System.Data.Entity.Migrations.MigrationsDomainCommand.Execute(Action command)
No migrations configuration type was found in the assembly 'Nop.Plugin.Payments.Deposit'. (In Visual Studio you can use the Enable-Migrations command from Package Manager Console to add a migrations configuration).

我读了很多相同的问题，到处都是原因是在 Enable-Migrations cmdlet 中指定了错误的项目（没有定义上下文）。但正如您所见，这不是我的情况。

还有什么原因？

Answer 1

您还需要添加 -ProjectName 参数来指定您希望迁移到的位置。例如：

Enable-Migrations -ProjectName Nop.Plugin.Payments.Deposit -StartUpProjectName nop.web -ContextProjectName Nop.Plugin.Payments.Deposit -verbose

它应该默认为您在控制台中选择的项目window。 https://coding.abel.nu/2012/03/ef-migrations-command-reference/

Answer 2

太好了，我已经成功解决了这个问题。

为了调查，我下载了 Entity Framework 的源代码并检查了异常堆栈中提到的所有方法。在方法 System.Data.Entity.Utilities.TypeFinder.FindType 中我找到了这样的指令：

var types = _assembly.GetAccessibleTypes()
                                 .Where(t => baseType.IsAssignableFrom(t));

这让我找到了 GetAccessibleTypes() 方法，我发现了这个：

return assembly.DefinedTypes.Select(t => t.AsType());

Having DefinedTypes 是属性 of System.Reflection.Assembly class 我试图通过在 Powershell 中加载我的程序集并获取此 [=45] 来手动获取此属性 =]:

$a = [System.Reflection.Assembly]::LoadFrom("P:\nopCommerce\Presentation\Nop.Web\Plugins\Payments.Deposit\Nop.Plugin.Payments.Deposit.dll")
$a.DefinedTypes

结果是空的，因为根本没有类型。

所以我尝试以不同的方式获取类型：

$a.GetTypes()

结果出错：

Exception calling "GetTypes" with "0" argument(s): "Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information."

当我检查 LoaderException 属性时，我发现了以下内容：

$Error[0].Exception.InnerException.LoaderExceptions

Could not load file or assembly 'Autofac, Version=3.5.0.0, Culture=neutral, PublicKeyToken=17863af14b0044da' or one of its dependencies. The system cannot find the file specified. Could not load file or assembly 'Nop.Services, Version=3.8.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified. Could not load file or assembly 'System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified. Could not load file or assembly 'System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified. Could not load file or assembly 'System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified. Could not load file or assembly 'System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

看起来 .NET 试图加载所有程序集，我的程序集依赖但当然不能，因为它们不在同一个文件夹中，因为它们是共享的，位于其他地方并由启动项目加载，而不是我的。

因此，我已将所有必需的程序集复制到与我相同的文件夹中，并再次尝试 Enable-Migrations。这次执行没有任何错误！

我问自己为什么不 Enable-Migrations 加载所有这些程序集本身，因为它需要考虑启动项目。但这是个小问题。

在程序集 EF6 中找不到上下文类型

No context type was found in the assembly EF6

entity-framework-6

nopcommerce

entity-framework-migrations