Question

我从Linq查询中收到以下错误：

ExecuteReader需要一个开放且可用的连接。该连接的当前状态是打开的。

如果需要打开连接，并且连接已打开...为什么这是一个错误？

关于此错误的堆栈溢出是post，解决方案是：

“基本上，我们的应用程序中有一些'流氓查询' 正在影响整个工作正常，所以我们只是通过每个班级（所有88个！）并检查他们是谁写得不错。“

我试图查询我的查询问题而不能。我测试了它，它得到了正确的结果..
这是我的疑问：

int? result = Helper.GetResult(b).FirstOrDefault();
if (result.HasValue)
     //something
-----------------------------------------------------------
Inside Helper: 

private static PingDbDataContext pingDataContext = new PingDbDataContext(); 
public static IQueryable<int?> GetResult(string b)
{
    pingDataContext.CommandTimeout = 5000;
    pingDataContext.Log = new DebugTextWriter();
    var q = from a in pingDataContext.SomeTable
            where a.SomeColumn == b
            select a.id;
    return q;
}

这是堆栈跟踪：

Exception information: 
    Exception type: InvalidOperationException 
    Exception message: ExecuteReader requires an open and available Connection. The connection's current state is open.
   at System.Data.SqlClient.SqlConnection.GetOpenConnection(String method)
   at System.Data.SqlClient.SqlConnection.ValidateConnectionForExecute(String method, SqlCommand command)
   at System.Data.SqlClient.SqlCommand.ValidateCommand(String method, Boolean async)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
   at System.Data.Linq.SqlClient.SqlProvider.Execute(Expression query, QueryInfo queryInfo, IObjectReaderFactory factory, Object[] parentArgs, Object[] userArgs, ICompiledSubQuery[] subQueries, Object lastResult)
   at System.Data.Linq.SqlClient.SqlProvider.ExecuteAll(Expression query, QueryInfo[] queryInfos, IObjectReaderFactory factory, Object[] userArguments, ICompiledSubQuery[] subQueries)
   at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query)
   at System.Data.Linq.DataQuery`1.System.Linq.IQueryProvider.Execute[S](Expression expression)
   at System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source)
   at MyProject.Controllers.MyController.Index() in (path...)\MyProject\Controllers\MyController.cs:line 53
   at lambda_method(Closure , ControllerBase , Object[] )
   at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
   at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClassd.<InvokeActionMethodWithFilters>b__a()
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
   at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)
   at System.Web.Mvc.Controller.ExecuteCore()
   at System.Web.Mvc.MvcHandler.<>c__DisplayClass8.<BeginProcessRequest>b__4()
   at System.Web.Mvc.Async.AsyncResultWrapper.<>c__DisplayClass1.<MakeVoidDelegate>b__0()
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Answer 1

由于这是一个MVC项目，并且您的数据上下文是一个静态变量，因此很可能是一个并发问题，就像BrokenGlass建议的那样。可以肯定的是，尝试在方法中创建数据上下文，如下所示：

public static IEnumerable<int?> GetResult(string b)
{
    using (PingDbDataContext pingDataContext = new PingDbDataContext())
    {
        pingDataContext.CommandTimeout = 5000;
        pingDataContext.Log = new DebugTextWriter();
        var q = from a in pingDataContext.SomeTable
                where a.SomeColumn == b
                select a.id;
        return q.ToList();
    }
}

问题是否仍然存在？

编辑：我已经重写了上述方法。您不应该在数据上下文范围之外返回IQueryable。在处理数据之前，您需要从数据库中检索数据。但是，无论如何，我都不会想到将IQueryable暴露在您的数据访问代码之外。如果您想修改在方法之外运行的查询，则只需要这样做。

Linq查询中的异常（MVC2）

1 个答案: