how to use TypeConverters to convert a System.Datetime to custom type

Question

For some reason I need to cast/convert a DateTime into one of many custom objects

This proves to be very difficult to do in a nice generic fashion.

I am thinking of implementing an extension method on object or perhaps extending DateTimeConverter.

But then what would be the generic way to handle this, I have an object and a destination type and at the moment I am using System.ConvertTo(..) but this is clearly limited because it only supports converting to .NET types and cant be extended.

Any ideas?

Answer 1

I can quite understand the intitial reaction to this: why in the hell do you want to do that..

Its tempting for me to say "trust me" but for anyone with 2 minutes of patience let me explain, maybe I have this back to front:

I have a db and a LINQ to SQL DataContext

My datacontext objects supply a more complex object model.

LINQ to SQL only supports mapping to certain types and does not support Many to many relationships and leaves me having to hard code the mapping.

I use reflection to populate "real world" object Properties from DataContext objects.

The real world object has more complex types such a TimeStamp (DateTime with extended functionality). So during this stage I have to convert a L2SQL generated System.DateTime object to my TimeStamp object.

Still following??

Ok so the problem is in 95% of cases the method correctly converts L2SQL types to the correct destination type e.g numeric(3,0) => (LINQ) System.Decimal => Int (real world object).

But I have properties that are wrappers for DateTime with extra functionality, clearly the raw value is a DateTime so when I save to the database a DateTime is sufficient. But when it comes back from the database I cannot get that sql datetime into my TimeStamp object...

I am now resigned to writing code along the lines you suggested:

if LINQ type == DateTime and destination == TimeStamp then .....

but I thought there must be a nice way to convert DateTime to some other type..

Maybe not.

Answer 2

You could add a constructor for your TimeStamp that takes DateTime as a parameter.

public class TimeStamp
{
   public TimeStamp(DateTime dateTime, ...)
   {
    // Your code here to convert from dateTime to TimeStamp
   }
}

Then later ...

 DestType Convert<DestType>( Object linqResult )   
 {
  DestType result;
  if( linqResult is DateTime && DestType is TimeStamp )
  {
   DateTime dbTime = linqResult as DateTime;
   result = new TimeStamp( dbTime );
  }
  ...
  return result;
 }

You could probably even extend this with all kinds of reflection and constructors etc. But if you want to base one object off of another (like a time stamp from a date time) a constructor seems natural.

Hope this helps, TJB

Answer 3

TJB thats exactly what I settled on and its working nicely.

Thanks