How to get nullable DateTime out of the database

Question

My SQL Server database contains nullable DateTime values. How can I convert them to a nullable DateTime object in my application in C#?

This is what I would think it

Answer 1

A while ago, I wrote a bunch of extension methods for a DataRow to do just this sort of downcasting...because I hate writing repetitive drivel. Usage is simple:

foreach( DataRow dr in someDataTable )
{
  DateTime? dt = dr.CastAsDateTimeNullable( "lastUpdated" ) ;
  int       id = dr.CastAsInt( "transactionID" ) ;
  // etc.
}

Here's the piece for DateTime values. Adding implementation for for other data types should be pretty trivial. Wouldn't be difficult to do the same sort of thing to a DataReader if one was so inclined.

I tried to come up with generic methods, but limitations in the way generics are done made it difficult or impossible to do and still get the behavior I wanted (e.g., null values rather than default(T) — getting default values for SQL NULLs that would make differentiating between 0 and null...difficult).

public static class DataRowExtensions
{

  #region downcast to DateTime

  public static DateTime CastAsDateTime( this DataRow row , int index )
  {
    return toDateTime( row[index] ) ;
  }
  public static DateTime CastAsDateTime( this DataRow row , string columnName )
  {
    return toDateTime( row[columnName] ) ;
  }

  public static DateTime? CastAsDateTimeNullable( this DataRow row , int index )
  {
    return toDateTimeNullable( row[index] );
  }
  public static DateTime? CastAsDateTimeNullable( this DataRow row , string columnName )
  {
    return toDateTimeNullable( row[columnName] ) ;
  }

  #region conversion helpers

  private static DateTime toDateTime( object o )
  {
    DateTime value = (DateTime)o;
    return value;
  }

  private static DateTime? toDateTimeNullable( object o )
  {
    bool  hasValue = !( o is DBNull );
    DateTime? value    = ( hasValue ? (DateTime?) o : (DateTime?) null ) ;
    return value;
  }

  #endregion

  #endregion downcast to DateTime

  // ... other implementations elided .. for brevity

}