entity-framework - Entity Framework : Value cannot be null. 参数名称:类型

Question

当我执行update-database命令时，它显示此错误消息

System.ArgumentNullException: Value cannot be null.
Parameter name: type

at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
at System.Activator.CreateInstance(Type type, Object[] args)
at System.Data.Entity.Migrations.Extensions.ProjectExtensions.GetProjectTypes(Project project, Int32 shellVersion)
at System.Data.Entity.Migrations.Extensions.ProjectExtensions.IsWebSiteProject(Project project)
at System.Data.Entity.Migrations.Extensions.ProjectExtensions.GetTargetDir(Project project)
at System.Data.Entity.Migrations.MigrationsDomainCommand.GetFacade(String configurationTypeName, Boolean useContextWorkingDirectory)
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)

Value cannot be null.
Parameter name: type"?

Answer 1

解决方案:对我来说，解决方案就像重新启动Visual Studio一样容易。

Senario:我有这样的解决方案:



我将启动项目从Host更改为包含web.config的UI.Web项目，然后运行update-database命令，但它给了Value cannot be null.异常，直到我重新启动Visual Studio并重新运行update-database命令。这次它表现正常。