Assigning `null` value to Nullable<DateTime> with single line 'if'

Question

I have a Class like this

public class MyClass {     public int Id { get; set; }     public Nullable<DateTime> ApplicationDate { get; set; }     .... } 

Now I'm trying to fill an object of MyClass like this

DataTable dt = DBHelper.GetDataTable(sql, conn); DataRow dr = dt.Rows[0];  MyClass oMyClass = new MyClass(); oMyClass.Id = (int)dr["Id"]; oMyClass.ApplicationDate = dr["ApplDate"] == DBNull.Value ? null : Convert.ToDateTime(dr["AppDate"]);  //Above line gives an error .... 

Assigning of Application Date value gives an error

Type of conditional expression cannot be determined because there is no implicit conversion between '<null>' and 'System.DateTime'

What am I missing here?

Answer 1

You need to cast null to DateTime?:

oMyClass.ApplicationDate = dr["ApplDate"] == DBNull.Value      ? (DateTime?)null      : Convert.ToDateTime(dr["AppDate"]);  

This is because of the way the compiler determines the resulting type of the conditional operator; the behavior is by design:

Either the type of first_expression and second_expression must be the same, or an implicit conversion must exist from one type to the other.

Since null by itself is of null type and thus there is no conversion from or to it, you need to help the compiler by casting.