复制EntityFramework.SqlServer.dll即可 进入bin文件夹

我抛出了相同的异常。我包括

using System.Data; 
using System.Data.Entity;

一切都恢复正常了。

In my case, everything was working properly then suddenly stopped worked because I think Resharper altered some changes which caused the problem. My project was divided into the data layer, service and presentation layer. I had Entity framework installed and referenced in my data layer but still the error didn't go away. Uninstalling and reinstalling didn't work either. Finally, I solved it by making the data layer the Startup project, making migration, updating the database and changing the Startup project back to my presentation layer.

删除bin文件夹帮我解决了这个问题

添加这个函数

private void FixEfProviderServicesProblem()

到库类中的数据库上下文类，丢失的DLL EntityFramework.SqlServer.dll将被复制到正确的位置。

namespace a.b.c
{
    using System.Data.Entity;

    public partial class WorkflowDBContext : DbContext
    {
        public WorkflowDBContext()
            : base("name=WorkflowDBConnStr")
        {
        }

        public virtual DbSet<WorkflowDefinition> WorkflowDefinitions { get; set; }
        public virtual DbSet<WorkflowInstance> WorkflowInstances { get; set; }
        public virtual DbSet<EngineAlert> EngineAlerts { get; set; }
        public virtual DbSet<AsyncWaitItem> AsyncWaitItems { get; set; }
        public virtual DbSet<TaskItem> TaskItems { get; set; }
        public virtual DbSet<TaskItemLink> TaskItemLinks { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
        }

        private void FixEfProviderServicesProblem()
        {
            // The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer'
            // for the 'System.Data.SqlClient' ADO.NET provider could not be loaded. 
            // Make sure the provider assembly is available to the running application. 
            // See http://go.microsoft.com/fwlink/?LinkId=260882 for more information.
            var instance = System.Data.Entity.SqlServer.SqlProviderServices.Instance;
        }
    }
}

.

引用实体框架所在项目的启动项目需要在bin文件夹中包含以下两个程序集:

EntityFramework.dll EntityFramework.SqlServer.dll

在启动项目的.config文件的<configSections>中添加<section>将使第一个程序集在该bin目录中可用。你可以从实体框架项目的.config文件中复制:

<configSections>
    <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
    <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
</configSections>

要使第二个.dll在bin文件夹中可用，尽管不实际，但可以从实体框架项目的bin文件夹中手动复制。 一个更好的选择是在实体框架项目的Post-Build Events中添加以下几行，这将使该过程自动化:

cd $(ProjectDir)
xcopy /y bin\Debug\EntityFramework.SqlServer.dll ..\{PATH_TO_THE_PROJECT_THAT_NEEDS_THE_DLL}\bin\Debug\