c# - 为什么 Entity Framework 6.1.3 会抛出 "Could not load type ' System.Data.Entity.Infrastructure.TableExistenceChecker'”

Question

由于上下文实例一创建就抛出异常，全新的项目和 Entity Framework 将无法启动。

Entity Framework 抛出以下异常:

Could not load type 'System.Data.Entity.Infrastructure.TableExistenceChecker' from assembly 'EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

引用资料:

• Entity Framework
• EntityFramework.SqLServer

通过 nuget 包管理器:

Install-Package entityframework

非常简单的上下文和实体:

public class TextDbContext : DbContext
{
    public TextDbContext()
        : base("Test")
    {
    }

    public DbSet<TestEntity> TestEntity { get; set; }
}

public class TestEntity
{
    public int Id { get; set; } 
    public string Name { get; set; }
}

static void Main(string[] args)
{
    var test = ConfigurationManager.ConnectionStrings["Test"].ConnectionString;

    using (var conn = new SqlConnection(test))
    {
        conn.Open();
        var cmd = new SqlCommand("Select * from testtable", conn);
        var result = cmd.ExecuteReader();
    }
    //exception thrown on this line is the same as the one in the context
    var instance = SqlProviderServices.Instance;

    using (var db = new TextDbContext())
    {
         var item = new TestEntity
         {
             Name = "xyz"
         };
         db.TestEntity.Add(item);
         db.SaveChanges();
    }
}

这是当前的 app.config 文件:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <configSections>
        <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral,  PublicKeyToken=b77a5c561934e089" requirePermission="false" />
    </configSections>
    <connectionStrings>
        <add name="Test" connectionString="server=localhost;database=Test;Data Source=localhost;Integrated Security=True;Pooling=True" providerName="System.Data.SqlClient" />
    </connectionStrings>
    <startup>
       <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
    <entityFramework>
        <defaultConnectionFactory type="System.Data.Entity.Infrastructure.SqlConnectionFactory, EntityFramework" />
         <providers>
            <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
        </providers>
    </entityFramework>
</configuration>

堆栈轨迹如下:

   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Reflection.RuntimePropertyInfo.GetValue(Object obj, BindingFlags invokeAttr, Binder binder, Object[] index, CultureInfo culture)
   at System.Reflection.RuntimePropertyInfo.GetValue(Object obj, Object[] index)
   at System.Data.Entity.Utilities.MemberInfoExtensions.GetValue(MemberInfo memberInfo)
   at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(Type providerType)
   at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName)
   at System.Data.Entity.Internal.AppConfig.<.ctor>b__2(ProviderElement e)
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at System.Data.Entity.Internal.AppConfig.<.ctor>b__1()
   at System.Lazy`1.CreateValue()
   at System.Lazy`1.LazyInitValue()
   at System.Lazy`1.get_Value()
   at System.Data.Entity.Internal.AppConfig.get_DbProviderServices()
   at System.Data.Entity.Infrastructure.DependencyResolution.AppConfigDependencyResolver.RegisterDbProviderServices()
   at System.Data.Entity.Infrastructure.DependencyResolution.AppConfigDependencyResolver.GetServiceFactory(Type type, String name)
   at System.Data.Entity.Infrastructure.DependencyResolution.AppConfigDependencyResolver.<>c__DisplayClass1.<GetService>b__0(Tuple`2 t)
   at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at System.Data.Entity.Infrastructure.DependencyResolution.AppConfigDependencyResolver.GetService(Type type, Object key)
   at System.Data.Entity.Infrastructure.DependencyResolution.DbDependencyResolverExtensions.GetServiceAsServices(IDbDependencyResolver resolver, Type type, Object key)
   at System.Data.Entity.Infrastructure.DependencyResolution.AppConfigDependencyResolver.GetServices(Type type, Object key)
   at System.Data.Entity.Infrastructure.DependencyResolution.ResolverChain.<>c__DisplayClass6.<GetServices>b__5(IDbDependencyResolver r)
   at System.Linq.Enumerable.<SelectManyIterator>d__14`2.MoveNext()
   at System.Linq.Enumerable.<ConcatIterator>d__71`1.MoveNext()
   at System.Linq.Enumerable.<OfTypeIterator>d__aa`1.MoveNext()
   at System.Data.Entity.Utilities.IEnumerableExtensions.Each[T](IEnumerable`1 ts, Action`1 action)
   at System.Data.Entity.Infrastructure.DependencyResolution.InternalConfiguration.Lock()
   at System.Data.Entity.Infrastructure.DependencyResolution.DbConfigurationManager.<.ctor>b__1()
   at System.Lazy`1.CreateValue()
   at System.Lazy`1.LazyInitValue()
   at System.Lazy`1.get_Value()
   at System.Data.Entity.Infrastructure.DependencyResolution.DbConfigurationManager.GetConfiguration()
   at System.Data.Entity.DbContext.InitializeLazyInternalContext(IInternalConnection internalConnection, DbCompiledModel model)
   at System.Data.Entity.DbContext..ctor(String nameOrConnectionString)
   at test2.TextDbContext..ctor() in \\srv\users\carl.tierney\Documents\Visual Studio 2013\Projects\test2\test2\test2context.cs:line 13
   at test2.Program.Main(String[] args) in \\srv\users\carl.tierney\Documents\Visual Studio 2013\Projects\test2\test2\Program.cs:line 13
   at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state
   at System.Threading.ThreadHelper.ThreadStart()

Answer 1

如果您像我一样发现 Gac 中没有安装 EF，那么下一步就是在记下软件包的版本后将其卸载。我使用 NuGet，所以我去了 Tools...Library Package Manager...Package Manager Console。我首先尝试了 GUI，但卸载失败，在撰写本文时，您只能安装最新版本的软件包。

1. 打开您的解决方案并转到工具...库包管理器...包管理器控制台
2. 选择使用 EF 并遇到问题的项目
3. 键入 Uninstall-package EntityFramework
4. 系统应该会提示您重新启动 Visual Studio，因此请关闭并重新打开 VS 和您的解决方案
5. 使用工具打开包管理器控制台...库包管理器...包管理器控制台
6. 键入 Install-package EntityFramework(如果要安装旧版本，请添加 -Version x.x.x)
7. 你应该可以走了