异常描述 System.InvalidOperationException HResult=0x80131509 Message=Nullable object must have a value. Source=System.Private.CoreLib StackTrace: at System.ThrowHelper.ThrowInvalidOperationException_InvalidOperatio
///<summary>///解决问题: efcore group new dynamic对象时生成int 型而不是 int? 而导致 Nullable object must have a value.的问题///</summary>publicclassGroupTableViewModel{///<summary>///Key///</summary>publicint? Id {get;set; }///<summary>///Count///</summary>publicint? Count {ge...
This example shows how to use method syntax on the results of a query clause. Just enclose the query expression in parentheses, and then apply the dot operator and call the method. In the following example, query #7 returns a count of the numbers whose value is between 3 and 7. C# Cop...
This example shows how to use method syntax on the results of a query clause. Just enclose the query expression in parentheses, and then apply the dot operator and call the method. In the following example, query #7 returns a count of the numbers whose value is between 3 and 7. ...
In the following example, query #7 returns a count of the numbers whose value is between 3 and 7. csharp Copy // Query #7. // Using a query expression with method syntax var numCount1 = ( from num in numbers1 where num is > 3 and < 7 select num ).Count(); // Better: ...
LongCount<TSource>(ParallelQuery<TSource>, Func<TSource,Boolean>) 返回一个 Int64,表示并行序列中满足条件的元素的数量。 Max(ParallelQuery<Decimal>) 返回值的并行序列中的最大值。 Max(ParallelQuery<Double>) 返回值的并行序列中的最大值。 Max(ParallelQuery<Int32>) 返回值的并行序列中的最大值。
Object Queryable 注解 Queryable类中声明的方法集提供了用于查询实现IQueryable<T>数据源的标准查询运算符的实现。 标准查询运算符是遵循 LINQ 模式的常规用途方法,使你能够对任何数据表达遍历、筛选和投影操作。基于 NET 的编程语言。 此类中的大多数方法定义为扩展IQueryable<T>类型的扩展方法。 这意味着它们可以像...
问InvalidOperationException出现在Linq orderby子句中ENprivate void SetTextReadOnly(Control ctr, bool ...
Count<TSource>(IEnumerable<TSource>) シーケンス内の要素の数を返します。 Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) 指定したシーケンス内の 1 つの条件を満たす要素の数を表す数値を返します。 CountBy<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEquality...
Determines whether a sequence contains a specified element by using a specified IEqualityComparer<T>. Count<TSource>(IEnumerable<TSource>) Returns the number of elements in a sequence. Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) Returns a number that represents how many elements...