EF 6-运行启用迁移时，EntityType没有定义键

我正在尝试启动EF6。并停留在此错误：EntityType'任务'没有定义键。定义此EntityType的键。

我了解这是一个常见错误，并且Google搜索导致许多博客/文章介绍了如何解决未定义的“键”。但是我无法解决。我的实体位于单独的库中，我不愿意使用注释方法来解决此问题。我计划使我的实体库远离任何依赖关系。

这是我的模式：

public class Task
    {

        public int Id { get; set; }
        public string Name { get; set; }
        public DateTime Due { get; set; }
        public int Priority { get; set; }
    }

这是我的上下文：

   public class TaskManagerContext : DbContext
    {
        public TaskManagerContext() : base("TMConnection") { 


        }

        public DbSet<Task> Tasks { get; set; }
    }

当我运行时Enable-Migrations，出现以下错误：

PM> Enable-Migrations -Force
Checking if the context targets an existing database...
System.Data.Entity.ModelConfiguration.ModelValidationException: One or more validation errors were detected during model generation:

TaskManager.DataLayer.Task: : EntityType 'Task' has no key defined. Define the key for this EntityType.
Tasks: EntityType: EntitySet 'Tasks' is based on type 'Task' that has no keys defined.

   at System.Data.Entity.Core.Metadata.Edm.EdmModel.Validate()
   at System.Data.Entity.DbModelBuilder.Build(DbProviderManifest providerManifest, DbProviderInfo providerInfo)
   at System.Data.Entity.DbModelBuilder.Build(DbConnection providerConnection)
   at System.Data.Entity.Internal.LazyInternalContext.CreateModel(LazyInternalContext internalContext)
   at System.Data.Entity.Internal.RetryLazy`2.GetValue(TInput input)
   at System.Data.Entity.Internal.LazyInternalContext.InitializeContext()
   at System.Data.Entity.Internal.LazyInternalContext.get_ModelBeingInitialized()
   at System.Data.Entity.Infrastructure.EdmxWriter.WriteEdmx(DbContext context, XmlWriter writer)
   at System.Data.Entity.Utilities.DbContextExtensions.<>c__DisplayClass1.<GetModel>b__0(XmlWriter w)
   at System.Data.Entity.Utilities.DbContextExtensions.GetModel(Action`1 writeXml)
   at System.Data.Entity.Utilities.DbContextExtensions.GetModel(DbContext context)
   at System.Data.Entity.Migrations.DbMigrator..ctor(DbMigrationsConfiguration configuration, DbContext usersContext, DatabaseExistenceState existenceState, Boolean calledByCreateDatabase)
   at System.Data.Entity.Migrations.DbMigrator..ctor(DbMigrationsConfiguration configuration)
   at System.Data.Entity.Migrations.Design.MigrationScaffolder..ctor(DbMigrationsConfiguration migrationsConfiguration)
   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.ScaffoldInitialCreate(String language, String rootNamespace)
   at System.Data.Entity.Migrations.EnableMigrationsCommand.<>c__DisplayClass2.<.ctor>b__0()
   at System.Data.Entity.Migrations.MigrationsDomainCommand.Execute(Action command)
One or more validation errors were detected during model generation:

TaskManager.DataLayer.Task: : EntityType 'Task' has no key defined. Define the key for this EntityType.
Tasks: EntityType: EntitySet 'Tasks' is based on type 'Task' that has no keys defined.