C# help with Extension Method - Converting collection to another type

Question

I want to convert from

 public class Party
 {
        public string Type { get; set; }
        public string Name { get; set; }
        public string Status { get; set;}
 }

and convert to

 public class Contact
 {
        public string Type { get; set; }
        public string Name { get; set; }
        public string Status { get; set;}
        public string Company {get;set;}
        public string Source {get;set;}    
 }

I tried using this extension method

   public static class EnumerableExtensions
    {
        public static IEnumerable<TTo> ConvertTo<TTo, TFrom>(this IEnumerable<TFrom> fromList)
        {
            return ConvertTo<TTo, TFrom>(fromList, TypeDescriptor.GetConverter(typeof(TFrom)));
        }

        public static IEnumerable<TTo> ConvertTo<TTo, TFrom>(this IEnumerable<TFrom> fromList, TypeConverter converter)
        {
            return fromList.Select(t => (TTo)converter.ConvertTo(t, typeof(TTo)));
        }
}

I get this error TypeConverter is unable to convert 'Party' to 'Contact'

    var parties = new List<Party>();
        parties.Add(new Party { Name = "name 1", Status = "status 1" });
        parties.Add(new Party { Name = "name 2", Status = "status 2" });

        var results = parties.ConvertTo<Contact, Party>().ToList();

What am I missing here?

Answer 1

There is no direct conversion between the type Party and the Type contact (polymorphic or inheritance based).

You need to implement a TypeConverter for your types so that .NET knows how to convert between those two types:

MSDN - TypeConverter Class

MSDN - How to Implement a TypeConverter

Once you create your TypeConverters, you have to decorate your two classes with the TypeConverterAttribute so that the Framework can get an instance of your TypeConverter at Runtime:

public class PartyTypeConverter : TypeConverter
{
    // Implementation
}

[TypeConverter(typeof(PartyTypeConverter)]
public class Party
{
    public string Type { get; set; }
    public string Name { get; set; }
    public string Status { get; set; }
}

You could also attempt to mimic the (what I'm guessing) is the desired behavior using LINQ (even though you'll lose the generic abilities):

var contacts = parties.Select(p => new Contact {
    Type = p.Type,
    Name = p.Name,
    Status = p.Status
});

Answer 2

here is a slightly different way, though at its core it still about simply copying member values from one object to another

add this to your Contact class

public static explicit operator Contact(Party p)
{
    return new Contact
    {
        Type = p.Type,
        Name = p.Name,
        Status = p.Status
    };
}

then convert like this:

List<Party> parties = new List<Party>();
parties.Add(new Party { Name = "Foo", Status = "Bar" });

parties.Select<Party, Contact>(p => (Contact)p)

you may want to enclose last bit into some extension method, but I don't see a point...