如何检查是否未分配DateTime变量? [英] How to check if DateTime variable is not assigned?

问题描述

如何检查是否未分配DateTime变量?

我想将一个"Myobject"对象传递给我的函数.像这样:

How to check if DateTime variable is not assigned?

I want to pass a ''Myobject'' object into my function. Like this:

public class Myobject
{
    public string Code { get; set; }
    public DateTime? StartDate { get; set; }

...

但是..该对象可能未分配StartDate.因此，我将从SQL中收到这样的错误:"SqlDateTime溢出.必须介于...之间."

我尝试过那样，但是没用:

But.. It is possible that this object will have not assigned StartDate. So, I will get an error from SQL like this: "SqlDateTime overflow. Must be between ..."

I tried like that, but it didn''t work:

...

using (SqlCommand sc = new SqlCommand("AddSchedule", sqlConnection))
{
    sc.CommandType = CommandType.StoredProcedure;
    sc.CommandTimeout = 100;
    sc.Transaction = transaction;

    if (_schedule.StartDate.HasValue)
    {
        sc.Parameters.Add(new SqlParameter("@inStartDate", _schedule.StartDate));
    }
    else
    {
        sc.Parameters.Add(new SqlParameter("@inStartDate", DBNull.Value));
    }
 
    using (sc.ExecuteReader())
    {
    }

}

请帮忙.

-------------------------------------------------- --------------------------------------------------

我仍然无法解决:/这太奇怪了！
再一次，非常简单的代码:

Please help.

----------------------------------------------------------------------------------------------------

I still can''t solve that:/ This is... weird!
Once again, VERY SIMPLE code:

public class Myobject
{
    public string Code { get; set; }
    public DateTime? StartDate { get; set; }
}

and PROGRAM:
MyObject mo = new MyObject();
mo.Code= "sth";
// NO action on StartDate property! 
 
    if (mo.StartDate.HasValue)
    {
        sc.Parameters.Add(new SqlParameter("@inStartDate", mo.StartDate.Value));
    }
    else
    {
        sc.Parameters.Add(new SqlParameter("@inStartDate", DBNull.Value));
    }

mo.StartDate.HasValue始终返回true ...
到底是什么?



我想要的只是这个如果":
如果(mo.StartDate.HasValue)
告诉我的是，是否使用了对象的DateTime属性-这就是我想要的.必须有一个简单的解决方案..

我什至尝试过

mo.StartDate.HasValue returns always true...
What the hell ?



All I want is this ''if'':
if (mo.StartDate.HasValue)
Something which tell me, if the DateTime property of the object was used or not - thats all I want. There must be an easy solution..

I even tried

MyObject mo = new MyObject();

if ((mo.StartDate.Value) == null) // This returns FALSE! HOW?!
{
    sc.Parameters.Add(new SqlParameter("@inStartDate", DBNull.Value));
}

推荐答案

您还必须注意，SQL DateTime的范围小于.NET类型的范围.

特别是，如果您使用的是smalldatetime，则默认值为DateTime 的值将超出SQL范围.

对于正常的SQL日期时间，使用DateTime.MaxValue会出现问题，因为SQL类型不太精确.舍入到SQL精度后，该值将为rangle，因为它将舍入到10000年.

You also have to be aware that the range of SQL DateTime is smaller than the range of .NET type.

In particular if you are using smalldatetime, then a DateTime with it default value would out of SQL range.

For normal SQL datetime, there is a problem using DateTime.MaxValue since SQL type is less precise. After rounding to SQL precision, the value would be of of rangle since it would round to year 10000.

尝试使用_schedule.StartDate.Value而不是_schedule.StartDate，并确保相应的SP参数为可以为空.

Try _schedule.StartDate.Value instead of _schedule.StartDate, and make sure the corresponding SP parameter is nullable.

您正在检查日期时间是否有值，但是SQL代码也会检查.例如，如果@date为null，则使用null，以检查是否传递了null，是否需要编写特殊情况代码来处理该问题.据我所知，真正的问题在于您的SP中，如果您的值为null，则您正在检查并传递null，因此您在C#中的代码很好.

You''re checking if your datetime has a value, but does your SQL code also check. Use is null as in, if @date is null, to check if you were passed a null, if you need to write special case code to deal with that. The real issue is in your SP as far as I can see, you''re checking and passing in a null if your value is null, so your code in C# is fine.

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