c# - 在我的 MVC 应用程序中添加迁移时，什么可能导致我的空对象异常？

Question

我已经在我的 mvc 应用程序中使用代码优先迁移很长时间了，它总是可以正常工作，但是今天，我收到了以下错误：

你调用的对象是空的。

这是在我添加了一个新模型之后开始的：

using System;
using System.ComponentModel.DataAnnotations;

namespace MyProject.Models
{
    public class Tab
    {
        public int Id { get; set; }
        [Display(Name = "Tab Name")]
        public string TabName { get; set; }
        [Display(Name = "Name")]
        public string UserName { get; set; }
        [Display(Name = "Email")]
        public string UserEmail { get; set; }
        [Display(Name = "Created")]
        public DateTime? CreatedAt { get; set; }
        [Display(Name = "Filter String")]
        public string FilterString { get; set; }
    }
}

我以与以前的表相同的方式添加了数据库上下文

public DbSet<Tab> Tabs { get; set; }

然后我添加了一个迁移，因为该表不存在

Add-Migration SomeName

它开始然后给我以下错误：

PM> Add-Migration Test
System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Data.Entity.Utilities.PropertyInfoExtensions.IsStatic(PropertyInfo property)
   at System.Data.Entity.Utilities.TypeExtensions.<GetInstanceProperties>b__22(PropertyInfo p)
   at System.Linq.Enumerable.WhereArrayIterator`1.MoveNext()
   at System.Data.Entity.Core.Metadata.Edm.MetadataPropertyCollection.ItemTypeInformation.GetItemProperties(Type clrType)
   at System.Data.Entity.Core.Metadata.Edm.MetadataPropertyCollection.<.cctor>b__0(Type clrType)
   at System.Data.Entity.Core.Common.Utils.Memoizer`2.<>c__DisplayClass2.<Evaluate>b__0()
   at System.Data.Entity.Core.Common.Utils.Memoizer`2.Result.GetValue()
   at System.Data.Entity.Core.Common.Utils.Memoizer`2.Evaluate(TArg arg)
   at System.Data.Entity.Core.Metadata.Edm.MetadataPropertyCollection.GetSystemMetadataProperties(MetadataItem item)
   at System.Data.Entity.Core.Metadata.Edm.MetadataItem.GetMetadataProperties()
   at System.Data.Entity.Core.Metadata.Edm.MetadataItem.get_Annotations()
   at System.Data.Entity.Edm.EdmModelVisitor.VisitMetadataItem(MetadataItem item)
   at System.Data.Entity.ModelConfiguration.Configuration.ConventionsConfiguration.ModelConventionDispatcher.VisitMetadataItem(MetadataItem item)
   at System.Data.Entity.Edm.EdmModelVisitor.VisitEdmAssociationType(AssociationType item)
   at System.Data.Entity.ModelConfiguration.Configuration.ConventionsConfiguration.ModelConventionDispatcher.VisitEdmAssociationType(AssociationType item)
   at System.Data.Entity.Edm.EdmModelVisitor.VisitCollection[T](IEnumerable`1 collection, Action`1 visitMethod)
   at System.Data.Entity.Edm.EdmModelVisitor.VisitAssociationTypes(IEnumerable`1 associationTypes)
   at System.Data.Entity.Edm.EdmModelVisitor.VisitEdmModel(EdmModel item)
   at System.Data.Entity.ModelConfiguration.Configuration.ConventionsConfiguration.ModelConventionDispatcher.VisitEdmModel(EdmModel item)
   at System.Data.Entity.ModelConfiguration.Configuration.ConventionsConfiguration.ModelConventionDispatcher.Dispatch()
   at System.Data.Entity.ModelConfiguration.Configuration.ConventionsConfiguration.ApplyConceptualModel(DbModel model)
   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.RunCore()
   at System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.Run()
Object reference not set to an instance of an object.
PM> 

除了早些时候断电导致应用程序崩溃之外，我所知道的一切都没有改变。这可能是无关的，但无论如何值得一提。

我能做些什么来潜在地解决这个问题？

标签： c#asp.net-mvcentity-frameworkentity-framework-migrations

Answer 1

尝试添加[Key]

using System;
using System.ComponentModel.DataAnnotations;

namespace MyProject.Models
{
    public class Tab
    {
        [Key]
        public int Id { get; set; }
        [Display(Name = "Tab Name")]
        public string TabName { get; set; }
        [Display(Name = "Name")]
        public string UserName { get; set; }
        [Display(Name = "Email")]
        public string UserEmail { get; set; }
        [Display(Name = "Created")]
        public DateTime? CreatedAt { get; set; }
        [Display(Name = "Filter String")]
        public string FilterString { get; set; }
    }
}