Add support for CreateProjection().ForMember(string name, ...)

[Mithras]

Please provide an overload for IProjectionExpression.ForMember() with string name instead of Expression<Func<TDestination, TMember>> destinationMember like you do in IMappingExpression.ForMember().

More context. I've tried to migrate from CreateMap() to CreateProjection() but where is no drop off replacement for ForMember(string name, ...). In our project we need to do something like

        foreach (var p in typeof(TDestination).GetProperties(BindingFlags.Public | BindingFlags.Instance))
        {
            source.ForMember(p.Name, x => x.ExplicitExpansion());
        }

because we use GraphQL and only map properties that are asked in a query.
In order to use CreateProjection() we now have to do something like this

        var destinationArg = Expression.Parameter(typeof(TDestination), "x");
        foreach (var p in typeof(TDestination).GetProperties(BindingFlags.Public | BindingFlags.Instance))
        {
            var propertyExpression = Expression.Property(destinationArg, p);
            var destinationMemberLambda = Expression.Lambda(propertyExpression, destinationArg);

            var configurationType = typeof(IProjectionMemberConfiguration<,,>).MakeGenericType(typeof(TSource), typeof(TDestination), p.PropertyType);
            var explicitExpansionMethod = configurationType.GetMethod("ExplicitExpansion");
            var configurationArg = Expression.Parameter(configurationType, "x");
            var explicitExpansionExpression = Expression.Call(configurationArg, explicitExpansionMethod);
            var explicitExpansionLambda = Expression.Lambda(explicitExpansionExpression, configurationArg);

            var forMemberMethod = typeof(IProjectionExpression<TSource, TDestination>).GetMethod("ForMember").MakeGenericMethod(p.PropertyType);
            forMemberMethod.Invoke(source, new object[] { destinationMemberLambda, explicitExpansionLambda.Compile() });
        }

which works fine but looks horrible and probably slows down our application start.

[lbargaoanu]

Try using ForAllMaps with ForAllMembers instead. Or ForAllPropertyMaps.

[jbogard]

We'd accept a PR for this feature request.

[lbargaoanu]

I'm not sure it's a good idea. Clearly ForAllMembers fits better here. And how many users we would have for such methods? People who need this kind of stuff can write an extension method or just just use CreateMap. I think these extra methods would only pollute intellisense and make for a worse user experience for most people.

[jbogard]

I think the original request is about a drop-in replacement for ForMember(string, memberOptions), which we don't have today. But yes I think in this case a ForAllMembers is better solution and not just an overload that takes a string.

[Mithras]

Yes, I would totally use ForAllMembers but I don't think it exists for IProjectionExpression today.

[Mithras]

There is no ForAllMembers for IProjectionExpression as far as I can tell.
I'll create a PR if you agree it's something you want.

[Mithras]

It really looks like a hack to me. I just want to use property name instead of expression. Why do I have to use ForAllMaps/ForAllPropertyMaps for this?

[lbargaoanu]

So you have only one map that uses explicit expansion for all members? :)

[Mithras]

Not one but not all of them either. Only Profiles with maps related to GraphQL

[lbargaoanu]

Yes, and using ForAllPropertyMaps in that profile only applies there, not globally. So one call would cover everything.

[Mithras]

Got it. I'll try it later today. Thank you!

[Mithras]

Update on this.

this.Internal().ForAllPropertyMaps(_ => true, (_, configuration) => configuration.ExplicitExpansion());

inside a Profile works fine but I still believe IProjectionExpression.ForMember() should have an overload which accepts property name. In my specific case I was able to workaround it by using Internal().ForAllPropertyMaps() but it might not be the same for other valid scenarios. I'm not even sure what's the reason behind forcing people to use expressions. In real world people have unit tests with ConfigurationProvider.AssertConfigurationIsValid() so I don't understand why we can't just use property name if we want to.

[lbargaoanu]

You can, just use CreateMap or the extension method above. ProjectTo is a query and queries work with types. 99.9% procent of the people don't use ForAllMembers or strings with ProjectTo, they just use dedicated DTOs. We should write new APIs for them, for the main use case, not for these weird corner cases. These kind of "features" represent API noise for most people in my view.
That being said, it seems to me that you replaced some reflection code and a setting per map with one line of code. I call that an improvement :)

[Mithras]

I don't share "everything but happy path is a corner case" idea.