Linq to SQL：System.Data.Linq.SqlClient.QueryConverter.VisitInvocation中的NullReferenceException（調用表達式調用）

Question

以下的L2S代碼位給了我這個非常奇怪的堆棧跟蹤。如果我附加調試器並在此調試器上設置斷點，則看起來問題在於評估transactions.Count（）。任何人都可以看到具體會導致這一點？請注意，Transaction表中沒有屬於此where子句的行。

的L2S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(); 
    } 
} 

退貨的交易;

堆棧跟蹤：

[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 

完全失去了在這一個。如果有人可以在這裏提供任何幫助，將不勝感激！

Answer 1

可能是t.Customer可以爲空嗎？你可以嘗試這樣的事情，看看有沒有工作沒有引發異常（假設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); 

Answer 2

你的一個子表的可能是罪魁禍首。我只是有這個錯誤，它是由於將一個空對象傳遞給一個輔助函數。不幸的是，你無法深入。