Question

我正在使用Linq2SQL运行查询，该查询归结为以下查询：



DateTime? expiration = GetExpirationDate();
IQueryable<Persons> persons = GetPersons();
IQueryable<Items> subquery = from i in db.Items
                             where i.ExpirationDate >= expiration
                             select i;

return persons.Where(p => p.Items != null && p.Items.Any(item => subquery.Contains(item)));

当我评估函数的结果时，我得到一个NullReferenceException，这里是堆栈跟踪。知道我做错了吗？！

基本上我想选择所有人并按项目到期日过滤它们。

   at System.Data.Linq.SqlClient.SqlFactory.Member(SqlExpression expr, MemberInfo member)
   at System.Data.Linq.SqlClient.QueryConverter.VisitMemberAccess(MemberExpression ma)
   at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp)
   at System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b)
   at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp)
   at System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b)
   at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp)
   at System.Data.Linq.SqlClient.QueryConverter.VisitWhere(Expression sequence, LambdaExpression predicate)
   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.Visit(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.VisitContains(Expression sequence, Expression value)
   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.Visit(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp)
   at System.Data.Linq.SqlClient.QueryConverter.VisitQuantifier(SqlSelect select, LambdaExpression lambda, Boolean isAny)
   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.Visit(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp)
   at System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b)
   at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node)
   at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp)
   at System.Data.Linq.SqlClient.QueryConverter.VisitWhere(Expression sequence, LambdaExpression predicate)
   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.Collections.Generic.IEnumerable.GetEnumerator()
   at System.Linq.SystemCore_EnumerableDebugView`1.get_Items()

Answer 1

expiration是否为空？也许有问题。

Answer 2

如果到期为空，则它仍然不是空引用（提示：引用）。

哈迪，问题是你编写了聪明的代码。而是编写可调试的代码。

Linq2SQL查询异常

2 个答案: