为什么以下代码会产生错误？
The query operator ‘ElementAtOrDefault’ is not supported
Dim Im = (From view In Db.Views Where _
view.Pass = txtCode.Text _
Select New With {.Id = view.UniqueID.ToString}_
).Distinct
Response.Redirect("~/test.aspx?x=" & Im(0).Id)
有没有办法在不使用FirstOrDefault选项的情况下修复它？
更新：这是StackTrace
at System.Data.Linq.sqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) at System.Data.Linq.sqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) at System.Data.Linq.sqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.sqlClient.QueryConverter.ConvertOuter(Expression node) at System.Data.Linq.sqlClient.sqlProvider.BuildQuery(Expression query,sqlNodeAnnotations annotations) 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.ElementAtOrDefault[TSource](IQueryable`1 source,Int32 index) at Login.btnLogin_Click(Object sender,EventArgs e) in D:\Projects\Memoria\Login.aspx.vb:line 14 at System.Web.UI.WebControls.Button.OnClick(EventArgs e) at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) at System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl,String eventArgument) at System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint,Boolean includeStagesAfterAsyncPoint)
解决方法
您需要做的是将.ToList()添加到查询的末尾.这应该工作：
Dim Im = (From view In Db.Views Where _
view.Pass = txtCode.Text _
Select New With {.Id = view.UniqueID.ToString}_
).Distinct.ToList()
Response.Redirect("~/test.aspx?x=" & Im(0).Id)
如果没有.ToList(),查询只返回一个DataQuery(Of T)而不是List(Of T).添加ToList调用有两个作用：
>强制查询立即执行,和
>返回支持ElementAtOrDefault()的集合类型
希望有所帮助！
