当我尝试在代码中首先启用mvc迁移时，我遇到了这个错误，但不明白这背后的原因是什么？

Question

错误：

  

上下文正在Code First模式中使用，代码是   从EDMX文件生成的数据库优先或模型优先   发展。这将无法正常工作。要解决这个问题，请不要   删除抛出此异常的代码行。如果你想使用   数据库优先或模型优先，然后确保实体   框架连接字符串包含在app.config或中   启动项目的web.config。如果你正在创建自己的   DbConnection，然后确保它是EntityConnection而不是   一些其他类型的DbConnection，并将它传递给其中一个   采用DbConnection的基础DbContext构造函数。了解更多   关于Code First，Database First和Model First，请参阅实体   这里的框架文档：   http://go.microsoft.com/fwlink/?LinkId=394715

我的web.config文件：

<?xml version="1.0" encoding="utf-8"?>
<!--
  For more information on how to configure your ASP.NET application, please visit
  http://go.microsoft.com/fwlink/?LinkId=301880
  -->
<configuration>

  <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>

  <connectionStrings>
    <add name="LibraryDBContext" connectionString="data source=.; database=LibraryDB; integrated security=true;" providerName="System.Data.SqlClient"/>
  </connectionStrings>
  <appSettings>
    <add key="webpages:Version" value="3.0.0.0" />
    <add key="webpages:Enabled" value="false" />
    <add key="ClientValidationEnabled" value="true" />
    <add key="UnobtrusiveJavaScriptEnabled" value="true" />
  </appSettings>
  <system.web>
    <compilation debug="true" targetFramework="4.5.1" />
    <httpRuntime targetFramework="4.5.1" />
  </system.web>
  <system.webServer>
    <handlers>
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <remove name="OPTIONSVerbHandler" />
      <remove name="TRACEVerbHandler" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
    </handlers>
  </system.webServer>
  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Helpers" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="1.0.0.0-5.0.0.0" newVersion="5.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Optimization" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="1.1.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Web.WebPages" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="WebGrease" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="0.0.0.0-1.5.2.14234" newVersion="1.5.2.14234" />
      </dependentAssembly>
    </assemblyBinding>
  </runtime>
  <entityFramework>
    <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
      <parameters>
        <parameter value="v11.0" />
      </parameters>
    </defaultConnectionFactory>
    <providers>
      <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
    </providers>
  </entityFramework>
</configuration>

上下文：

  public class LibraryDBContext:DbContext
    {
        public LibraryDBContext()
            : base("LibraryDBContext")
        {

        }
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        throw new UnintentionalCodeFirstException();
    }

    public virtual DbSet<Author> Authors { get; set; }
    public virtual DbSet<Book> Books { get; set; }
    public virtual DbSet<Category> Categories { get; set; }
    public virtual DbSet<Department> Departments { get; set; }
    public virtual DbSet<Desk> Desks { get; set; }
    public virtual DbSet<Faculty> Faculties { get; set; }
    public virtual DbSet<LibraryBuildingLevel> LibraryBuildingLevels { get; set; }
    public virtual DbSet<Librarian> Librarians { get; set; }
    public virtual DbSet<Publication> Publications { get; set; }
    public virtual DbSet<Shelf> Shelves { get; set; }
    public virtual DbSet<Student> Students { get; set; }
    public virtual DbSet<Teacher> Teachers { get; set; }
    public virtual DbSet<User> Users { get; set; }
    public virtual DbSet<UserType> UserTypes { get; set; }

}

}