Nullable datetime to datetime converter automapper

Question

I have a situation where my DTOs require DateTime properties but my POCOs use nullable datetimes. To avoid having to create ForMember mappings for every property with this condition I created an ITypeConverter<DateTime?, DateTime>. The problem I ran into is when both DTO and POCO have nullable DateTimes this converter is called. The DestinationType is DateTime even though the property is a nullable datetime. Any idea how I would make this converter run only for actual nullable datetimes?

public class FooDTO
{
    public DateTime? FooDate { get; set; }
}

public class FooPoco
{
    public DateTime? FooDate { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        Mapper.CreateMap<FooDTO, FooPoco>();
        Mapper.CreateMap<DateTime?, DateTime>()
              .ConvertUsing<NullableDateTimeConverter>();
        var poco = new FooPoco();
        Mapper.Map(new FooDTO() { FooDate = null }, poco);

        if (poco.FooDate.HasValue)
            Console.WriteLine(
                "This should be null : {0}",
                poco.FooDate.Value.ToString()); //Value is always set 
        else
            Console.WriteLine("Mapping worked");
    }
}

public class NullableDateTimeConverter : ITypeConverter<DateTime?, DateTime>
{
    // Since both are nullable date times and this handles converting
    // nullable to datetime I would not expect this to be called. 
    public DateTime Convert(ResolutionContext context)
    {
        var sourceDate = context.SourceValue as DateTime?;
        if (sourceDate.HasValue)
            return sourceDate.Value;
        else
            return default(DateTime);
    }
}

I found this post AutoMapper TypeConverter mapping nullable type to not-nullable type but it was little help.

Answer 1

Without looking I suspect its calling your TypeCoverter because its the best match for the types being converted.

If you create another TypeConverter with the correct types it should work fine. Eg:

public class DateTimeConverter : ITypeConverter<DateTime?, DateTime>
{
    public DateTime Convert(ResolutionContext context)
    {
        var sourceDate = context.SourceValue as DateTime?;
        if (sourceDate.HasValue)
            return sourceDate.Value;
        else
            return default(DateTime);
    }
}

public class NullableDateTimeConverter : ITypeConverter<DateTime?, DateTime?>
{
    public DateTime? Convert(ResolutionContext context)
    {
        var sourceDate = context.SourceValue as DateTime?;
        if (sourceDate.HasValue)
            return sourceDate.Value;
        else
            return default(DateTime?);
    }
}

Note that if you wish these can be further simplified to

public class DateTimeConverter : TypeConverter<DateTime?, DateTime>
{
    protected override DateTime ConvertCore(DateTime? source)
    {
        if (source.HasValue)
            return source.Value;
        else
            return default(DateTime);
    }
}

public class NullableDateTimeConverter : TypeConverter<DateTime?, DateTime?>
{
    protected override DateTime? ConvertCore(DateTime? source)
    {
        return source;
    }
}

Then just initialise both converters:

Mapper.CreateMap<DateTime?, DateTime>().ConvertUsing<DateTimeConverter>();
Mapper.CreateMap<DateTime?, DateTime?>().ConvertUsing<NullableDateTimeConverter>();
Mapper.AssertConfigurationIsValid();