我在 Linq To SQL 数据上下文上遇到空引用异常，我什至不知道从哪里开始

Question

我刚刚将用户和角色 asp 数据库部署到网站，但收到此异常

“对象引用未设置到对象的实例”。 描述：执行当前 Web 请求期间发生未处理的异常。请查看堆栈跟踪以获取有关错误及其在代码中的来源的更多信息。

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 41:   #endregion
Line 42:    
Line 43:    public UsersAndRolesDataContext() : 
Line 44:                base(global::System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString"    ].ConnectionString, mappingSource)
Line 45:    {


Source File: d:\hosting\7122544\html\SSM\App_Code\UsersAndRoles.designer.cs    Line: 43

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
   UsersAndRolesDataContext..ctor() in d:\hosting\7122544\html\SSM\App_Code    \UsersAndRoles.designer.cs:43
   admin_ManageUsers..ctor() in d:\hosting\7122544\html\SSM\admin\ManageUsers.aspx.cs:11
   ASP.admin_manageusers_aspx..ctor() in c:\windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\ssm\5b123e8f\6bb9cf4c\App_Web_tz5adhff.10.cs:0
   __ASP.FastObjectFactory_app_web_tz5adhff.Create_ASP_admin_manageusers_aspx() in     c:\windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\ssm\5b123e8f\6bb9cf4c\App_Web_tz5adhff.12.cs:0
   System.Web.Compilation.BuildResultCompiledType.CreateInstance() +32
   System.Web.Compilation.BuildManager.CreateInstanceFromVirtualPath(VirtualPath virtualPath, Type requiredBaseType, HttpContext context, Boolean allowCrossApp) +109
   System.Web.UI.PageHandlerFactory.GetHandlerHelper(HttpContext context, String requestType, VirtualPath virtualPath, String physicalPath) +31
   System.Web.UI.PageHandlerFactory.GetHandler(HttpContext context, String requestType, String virtualPath, String path) +37
   System.Web.MaterializeHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +334
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184

Answer 1

您可能在配置文件中缺少名为 ConnectionString 的连接字符串，因此 System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString" ] 返回 null。

Answer 2

您的 Web.config 或 App.config 中可能缺少连接字符串。确保您的文件中有类似于以下内容的内容。

<connectionStrings>
    <add name="AdventureWorksEntities" 
         connectionString="metadata=.\AdventureWorks.csdl|.\AdventureWorks.ssdl|.\AdventureWorks.msl;
         provider=System.Data.SqlClient;provider connection string='Data Source=localhost;
         Initial Catalog=AdventureWorks;Integrated Security=True;Connection Timeout=60;
         multipleactiveresultsets=true'" providerName="System.Data.EntityClient" />
</connectionStrings>