Mapping to immutable value object (record) requires both ForCtorParam and ForMember statements

[n-shay]

As my understanding and from my previous experience working with AutoMapper, constructor handling should work out of the box as long as the naming & type of the properties match to the constructor parameters, and it does... As long as you don't have to map any custom source expressions.

I found plenty of old posts on SO and others forums that suggest using ForCtorParam but I was surprised to see that the ForCtorParam doesn't replace ForMember but you must specify them both, for each property, which is redundant.

I solved it temporary by adding an extension method that adds them both, but would like to get your input whether it's the intended behavior, or rather I'm doing something wrong, or maybe there's a bug in the library.

Source/destination types

        public class Foo
        {
            public int OtherId { get; set; }
        }

        public record Bar(int Id);

Mapping configuration

        // this works...
        config.CreateMap<Foo, Bar>()
                .ForCtorParam(
                        nameof(Bar.Id),
                        m => m.MapFrom(x => x.OtherId))
                .ForMember(
                        x => x.Id,
                        m => m.MapFrom(x => x.OtherId));
        });

Version: 10.1.1

Expected behavior

Only .ForMember statement is needed to map a property with matching ctor parameter.

Actual behavior

If only .ForMember is provided, the following error occurs:

AutoMapper.AutoMapperConfigurationException

Unmapped members were found. Review the types and members below.
Add a custom mapping expression, ignore, add a custom resolver, or modify the source/destination type
For no matching constructor, add a no-arg ctor, add optional arguments, or map all of the constructor parameters
=================================================================================================================================
Foo -> Bar (Destination member list)
ObjectMappingTests+Foo -> ObjectMappingTests+Bar (Destination member list)

No available constructor.

If only .ForCtorParam is provided, the following error occurs:

AutoMapper.AutoMapperConfigurationException

Unmapped members were found. Review the types and members below.
Add a custom mapping expression, ignore, add a custom resolver, or modify the source/destination type
For no matching constructor, add a no-arg ctor, add optional arguments, or map all of the constructor parameters
=================================================================================================================================
Foo -> Bar (Destination member list)
ObjectMappingTests+Foo -> ObjectMappingTests+Bar (Destination member list)

Unmapped properties:
Id

Steps to reproduce

Using Xunit test:

        [Theory]
        [AutoData]
        public void FooBar(Foo bar)
        {
            var configuration = new MapperConfiguration(config =>
                                                        {
                                                            // both ForCtorParam and ForMember are required, if one is commented out, assertion (and Map) fail.
                                                            config.CreateMap<Foo, Bar>()
                                                                  .ForCtorParam(
                                                                       nameof(Bar.Id),
                                                                       m => m.MapFrom(x => x.OtherId))
                                                                  .ForMember(
                                                                       x => x.Id,
                                                                       m => m.MapFrom(x => x.OtherId));
                                                        });

            // Act
            configuration.AssertConfigurationIsValid();
            var mapper = new Mapper(configuration);
            var bar = mapper.Map<Bar>(foo);

            // Assert
            bar.Should()
               .NotBeNull()
               .And.Match((Bar o) => o.Id == foo.OtherId);
        }

[lbargaoanu]

Try the MyGet build.