存储在数据库中的日期为NULL的日期返回为01/01/1900，而不是DateTime.MinValue。

Question

I have a logic that does the following:

string myData =  Convert.ToDateTime(Info.ClosedDate) == DateTime.MinValue ? String.Empty : "(" + Info.ClosedDate + ")";

It should return ClosedDate in parenthesis if it is not stored as NULL in the database. Otherwise it should return an empty string.

The value of Convert.ToDateTime(Info.ClosedDate) is 01/01/1900 and the value of DateTime.MinValue is 1/1/0001 12:00:00 AM

So, the condition will never return String.Empty

Currently the field in the object is represent as :

public string ClosedDate
{
    get { return _ClosedDate; }
    set { _ClosedDate = value; }
}

What is the best solution?

Answer 1

Don't store or model DateTime types as string .

This applies to the data store but also to your models in the code. If it can be nullable in the database than model it as Nullable<DateTime> (alternate notation DateTime? ) in your code. Only convert it to a string at the last possible moment, usually in the presentation layer. If you do that there is no need to do any type conversion when reading/writing to the data store. You also avoid ambiguity on the value interpretation ( like what value is null or is it localized as "dd/MM/yyyy" or "MM/dd/yyyy" ).

private DateTime? _ClosedDate;
public DateTime? ClosedDate
{
    get { return _ClosedDate; }
    set { _ClosedDate = value; }
}

side note: the above could also be modeled as an auto property but I did not do so because it is not clear how the field is used in the model

If you are not sure how to pass a DateTime instance to an ADO.NET query as a parameter in it's native format please review this previous question/answer: How can I add user-supplied input to an SQL statement?

Answer 2

You can compare against SqlDateTime.MinValue

Convert.ToDateTime(Info.ClosedDate) == SqlDateTime.MinValue? String.Empty : "(" + Info.ClosedDate + ")";

https://docs.microsoft.com/en-us/dotnet/api/system.data.sqltypes.sqldatetime.minvalue?view=netframework-4.7.2

Answer 3

Although its best to use DateTime as type for dates, your code should like this:

public DateTime ClosedDate
{
    get; set;
}

You can also use auto properties like this or private set upto the requirements.

public DateTime ClosedDate 
{
   get;
   set
   {
     Date = DateTime.Now;
   }
}

For string, you can use DateTime.Parse or DateTime.ParseExact instead of Convert.ToDateTime .

If value is null then Parse or ParseExact returns ArgumentNullException and same way if value contains some invalid date format then it returns FormatException .

var convertedDate = DateTime.ParseExact(dateTime, "yyyyMMdd", CultureInfo.InvariantCulture);