Question

In our C# code I recently changed a line from inside a linq-to-sql select new query as follows:

OrderDate = (p.OrderDate.HasValue ? 
    p.OrderDate.Value.Year.ToString() + "-" + 
    p.OrderDate.Value.Month.ToString() + "-" + 
    p.OrderDate.Value.Day.ToString() : "")

To:

OrderDate = (p.OrderDate.HasValue ? 
    p.OrderDate.Value.ToString("yyyy-mm-dd") : "")

The change makes the line smaller and cleaner. It also works fine with our SQL 2008 database in our development environment. However, when the code deployed to our production environment which uses SQL 2005 I received an exception stating: Nullable Type must have a value. For further analysis I copied (p.OrderDate.HasValue ? p.OrderDate.Value.ToString("yyyy-mm-dd") : "") into a string (outside of a Linq statement) and had no problems at all, so it only causes an in issue inside my Linq. Is this problem just something to do with SQL 2005 using different date formats than from SQL 2008?

Here’s more of the Linq:

var FilteredOrders = [linq-to-sql query].AsEnumerable().ToList<Order>();

                dt = FilteredOrders.Where(x => x != null).Select(p =>
                new
                {
                    Order = p.OrderId,
                    link = "/order/" + p.OrderId.ToString(),
                    StudentId = (p.PersonId.HasValue ? p.PersonId.Value : 0),
                    FirstName = p.IdentifierAccount.Person.FirstName,
                    LastName = p.IdentifierAccount.Person.LastName,
                    DeliverBy = p.DeliverBy,
                    OrderDate = p.OrderDate.HasValue ? 
                        p.OrderDate.Value.Date.ToString("yyyy-mm-dd") : 
                        ""
                }).ToDataTable();

This is selecting from a List of Order objects.
The FilteredOrders list is from another linq-to-sql query and I call .AsEnumerable on it before giving it to this particular select new query.

Doing this in regular code works fine:

if (o.OrderDate.HasValue)
    tempString += " " + o.OrderDate.Value.Date.ToString("yyyy-mm-dd");

Here is the stack trace from the error. This is part of a large system at a school for retrieving orders for transcripts from the DB to show on screen.

Line 46:   
Line 47:            dt = FilteredOrders.Where(x => x != null).Select(p =>  
Line 48:            new  
Line 49:                     { 
Line 50:                         Order = p.OrderId,


Stack Trace:

[InvalidOperationException: Nullable object must have a value.]    System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource) +51    System.Nullable`1.get_Value() +1373881 Aqueduct.Platform.Web.packages.finance_carttranscriptorder_default.<PopulateSearchResultsGrid>b__1(CartTranscriptOrder p) in D:\Repositories\aqueduct\Aqueduct.Platform.Web\trunk\packages\finance\carttranscriptorder\default.aspx.cs:48 System.Linq.WhereSelectListIterator`2.MoveNext()
+107    System.Linq.Buffer`1..ctor(IEnumerable`1 source) +434    System.Linq.<GetEnumerator>d__0.MoveNext()
+108    Aqueduct.Core.Data.ObjectShredder`1.Shred(IEnumerable`1 source, DataTable table, Nullable`1 options) in D:\Repositories\aqueduct\Aqueduct.Core\trunk\Data\LinqExtensions.cs:116 Aqueduct.Core.Data.LinqExtensions.ToDataTable(IEnumerable`1 source) in D:\Repositories\aqueduct\Aqueduct.Core\trunk\Data\LinqExtensions.cs:49 Aqueduct.Platform.Web.packages.finance_carttranscriptorder_default.PopulateSearchResultsGrid(List`1 FilteredOrders) in D:\Repositories\aqueduct\Aqueduct.Platform.Web\trunk\packages\finance\carttranscriptorder\default.aspx.cs:47 Aqueduct.Platform.Web.packages.finance_carttranscriptorder_default.RunFilter() in D:\Repositories\aqueduct\Aqueduct.Platform.Web\trunk\packages\finance\carttranscriptorder\default.aspx.cs:101 Aqueduct.Platform.Web.packages.finance_carttranscriptorder_default.Page_Load(Object sender, EventArgs e) in D:\Repositories\aqueduct\Aqueduct.Platform.Web\trunk\packages\finance\carttranscriptorder\default.aspx.cs:22 System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e)
+14    System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35    System.Web.UI.Control.OnLoad(EventArgs e) +99    System.Web.UI.Control.LoadRecursive()
+50    System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +627

Answer 1

I suspect it’s trying to convert the code into SQL. If this is just the projection side of things, I suggest you do a simple projection to the bits of data you need within the LINQ-to-SQL bit, then use AsEnumerable to force the rest of the query to execute in .NET itself. At that point you can do things like this with a lot more freedom. So in this case you’d have something like:

var query = from ...
            where ...
            select new { p.OrderData, p.SomeOtherFields };

var transformed = query.AsEnumerable()
                       .Select(p => new {
   OrderDate = (p.OrderDate.HasValue ? p.OrderDate.Value.ToString("yyyy-mm-dd") 
                                     : ""),
   ... });