LINQ NullReferenceException on a simple selection

Question

The following code throws a NullReferenceException. If I filter user table using another column, exception is not throwed. DateTime type columns cause this exception.

using (MyDataContext dc = new MyDataContext())
    {
        var ids = dc.Users.Where(c => c.BirthDate < DateTime.Now.AddYears(-10)).Select(c => c.UserId);

        var list = (from c in dc.Users
                    where ids.Contains(c.UserId)
                    select c).ToList();
    }

Stack trace like this:

[NullReferenceException: Object reference not set to an instance of an object.]


System.Data.Linq.SqlClient.SqlFactory.Member(SqlExpression expr, MemberInfo member) +182
   System.Data.Linq.SqlClient.QueryConverter.VisitMemberAccess(MemberExpression ma) +260
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +939
   System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) +1011
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +1003
   System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitChangeType(Expression expression, Type type) +12
   System.Data.Linq.SqlClient.QueryConverter.VisitCast(UnaryExpression c) +117
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +619
   System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b) +35
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +427
   System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b) +35
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +427
   System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitWhere(Expression sequence, LambdaExpression predicate) +125
   System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) +3403
   System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) +74
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +1003
   System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitSelect(Expression sequence, LambdaExpression selector) +17
   System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) +1368
   System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) +74
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +1003
   System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitContains(Expression sequence, Expression value) +377
   System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) +9129
   System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) +74
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +1003
   System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) +18
   System.Data.Linq.SqlClient.QueryConverter.VisitWhere(Expression sequence, LambdaExpression predicate) +125
   System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) +3403
   System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) +74
   System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) +1003
   System.Data.Linq.SqlClient.QueryConverter.ConvertOuter(Expression node) +79
   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.Collections.Generic.IEnumerable<T>.GetEnumerator() +35
   System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) +7667686
   System.Linq.Enumerable.ToList(IEnumerable`1 source) +61
   lab_test.Page_Load(Object sender, EventArgs ee) in d:\Projeler\Kardelen\Kod\Kardelen.Web.UI\lab\test.aspx.cs:543
   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

Is anybody get this exception?

Thanks for response.

I had some errors in .Net when using a column of Type DateTime that contained Null values. I don't know about NULL values in Linq but try running your code against a table without NULL values in that column to check. Added: Or see what happens when you "add" -10 years to DateTime.MinValue? — Stephan B
– Stephan B, Commented Nov 30, 2011 at 12:15
Not the cause of your problem, but you probably shouldn't use DateTime.Now.AddYears(-10) within the Where clause. Define it once before so it is the same for all calls. As to your problem, I'm guessing BirthDate is simply null? — Steven Jeuris
– Steven Jeuris, Commented Nov 30, 2011 at 12:26
Steven Jeuris, when I declare DateTime.Now.AddYears(-10) before selection as a variable, the problem is solved. Thanks for reply. — selami
– selami, Commented Nov 30, 2011 at 12:32

Steven Jeuris · Accepted Answer · 2011-11-30 12:31:35Z

5

If I filter user table using another column, exception is not throwed. DateTime type columns cause this exception.

Assuming you mean this comparison: c.BirthDate < DateTime.Now.AddYears(-10)

Most likely BirthDate is null. In case it is sufficient in your scenario to just skip those users, you can add a check to see whether it is null before doing the date comparison.

As a sidenote, you should probably define DateTime.Now.AddYears(-10) once before calling Where to prevent it from being recalculated, and worse from the value changing over time.

DateTime tenYearsAgo = DateTime.Now.AddYears(-10);
var ids = dc.Users
    .Where(c => c.BirthDate != null && c.BirthDate < tenYearsAgo)
    .Select(c => c.UserId);

answered Nov 30, 2011 at 12:31

Steven Jeuris

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Comments

Henk Holterman · Accepted Answer · 2011-11-30 12:32:09Z

1

Most likely your c.BirthDate property is nullable , DateTime? BirthDate.

That would match an Allow-NULL column in your table.

A simple check should be enough:

 dc.Users.Where(c => c.BirthDate.HasValue 
       && (c.BirthDate < DateTime.Now.AddYears(-10))
 )

answered Nov 30, 2011 at 12:32

Henk Holterman

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