AutoMapper: "Ignore the rest"?

Question

Is there a way to tell AutoMapper to ignore all of the properties except the ones which are mapped explicitly?

I have external DTO classes which are likely to change from the outside and I want to avoid specifying each property to be ignored explicitly, since adding new properties will break the functionality (cause exceptions) when trying to map them into my own objects.

Answer 1

This is an extension method I wrote that ignores all non existing properties on the destination. Not sure if it will still be useful as the question is more than two years old, but I ran into the same issue having to add a lot of manual Ignore calls.

public static IMappingExpression<TSource, TDestination> IgnoreAllNonExisting<TSource, TDestination>
(this IMappingExpression<TSource, TDestination> expression)
{
    var flags = BindingFlags.Public | BindingFlags.Instance;
    var sourceType = typeof (TSource);
    var destinationProperties = typeof (TDestination).GetProperties(flags);

    foreach (var property in destinationProperties)
    {
        if (sourceType.GetProperty(property.Name, flags) == null)
        {
            expression.ForMember(property.Name, opt => opt.Ignore());
        }
    }
    return expression;
}

Usage:

Mapper.CreateMap<SourceType, DestinationType>()
                .IgnoreAllNonExisting();

UPDATE: Apparently this does not work correctly if you have custom mappings because it overwrites them. I guess it could still work if call IgnoreAllNonExisting first and then the custom mappings later.

schdr has a solution (as an answer to this question) which uses Mapper.GetAllTypeMaps() to find out which properties are unmapped and auto ignore them. Seems like a more robust solution to me.