Question

下面的L2S代码给了我这个非常奇怪的堆栈跟踪。如果我附加调试器并在此调试器的顶部设置断点，则问题似乎在于评估transactions.Count（）。任何人都可以看到具体是什么导致这个？请注意，Transactions表中没有属于此where子句的行。

L2S代码段

var transactions = (from t in DataContext.Transactions
                    where t.TransactionDate.Date == date.Date && company.Id == t.Customer.CompanyId
                    select t);

if (transactions.Count() > 0) // Exception thrown here (transactions.Count())
{
    foreach (var transaction in transactions)
    {
        transaction.Detach();
    }
}

退货交易;

堆栈跟踪：

[NullReferenceException: Object reference not set to an instance of an object.]
   System.Data.Linq.SqlClient.QueryConverter.VisitInvocation(InvocationExpression invoke) +471
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +1370
   System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) +30
   System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b) +27
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +449
   System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) +30
   System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b) +40
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +449
   System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) +30
   System.Data.Linq.SqlClient.QueryConverter.VisitWhere(Expression sequence, LambdaExpression predicate) +136
   System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) +4173
   System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) +70
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +1025
   System.Data.Linq.SqlClient.QueryConverter.VisitAggregate(Expression sequence, LambdaExpression lambda, SqlNodeType aggType, Type returnType) +84
   System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) +6371
   System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) +70
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +1025
   System.Data.Linq.SqlClient.QueryConverter.ConvertOuter(Expression node) +111
   System.Data.Linq.SqlClient.SqlProvider.BuildQuery(Expression query, SqlNodeAnnotations annotations) +114
   System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query) +132
   System.Data.Linq.DataQuery`1.System.Linq.IQueryProvider.Execute(Expression expression) +23
   System.Linq.Queryable.Count(IQueryable`1 source) +243
   MyProject.Repositories.TransactionRepository.GetTransactionsOn(DateTime date, Company company) in D:\Build\MyProject\Source\MyProject\Repositories\TransactionRepository.cs:38
   MyProject.Web.Widgets.RunningSalesTotalWidget.GetView() in D:\Build\MyProject\Source\MyProject\Web\Widgets\RunningSalesTotalWidget.cs:26
   MyProject.Web.WidgetController.Render(ViewContext viewContext) in D:\Build\MyProject\Source\MyProject\Web\WidgetController.cs:38
   MyProject.Web.Helpers.WidgetExtensions.RenderWidget(HtmlHelper helper, Int32 id) in D:\Build\MyProject\Source\MyProject.Web\Helpers\WidgetExtensions.cs:20
   ASP.views_home_index_aspx.__RenderContent2(HtmlTextWriter __w, Control parameterContainer) in d:\Build\MyProject\Source\MyProject.Web\Views\Home\Index.aspx:9
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +109
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.Control.Render(HtmlTextWriter writer) +10
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   ASP.views_shared_site_master.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in d:\Build\MyProject\Source\MyProject.Web\Views\Shared\Site.Master:30
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +109
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.Control.Render(HtmlTextWriter writer) +10
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +208
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.Page.Render(HtmlTextWriter writer) +29
   System.Web.Mvc.ViewPage.Render(HtmlTextWriter writer) +56
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3060

完全失去了这一个。如果有人可以在这里提供任何帮助，我们将不胜感激！

Answer 1

你的一个子表可能是罪魁祸首。我只是有这个错误，这是由于将一个null对象传递给一个辅助函数。不幸的是，你无法走得那么深。

Answer 2

可能t.Customer可以为空吗？您可以尝试这样的事情，看看它是否有效而不抛出异常（假设CompanyId是int）：

var transactions = (from t in DataContext.Transactions
                    where t.TransactionDate.Date == date.Date 
                        && company.Id == (t.Customer != null ? t.Customer.CompanyId : -1)
                    select t);

Linq to SQL：System.Data.Linq.SqlClient.QueryConverter.VisitInvocation（InvocationExpression invoke）中的NullReferenceException

2 个答案: