MapFrom doesn't resolve constructor parameters that have no matching source property

[spydacarnage]

Re-opening issue #2745 with additional details.

Source/destination types

public class Source
{
    public string Result { get; }

    public Source(string result)
    {
        Result = result;
    }
}

public class Dest
{
    public string Result{ get; }
    public dynamic Details { get; }

    public Dest(string result, DestInner1 inner1)
    {
        Result = result;
        Details = inner1;
    }
    public Dest(string result, DestInner2 inner2)
    {
        Result = result;
        Details = inner2;
    }

    public class DestInner1
    {
        public int Value { get; }

        public DestInner1(int value)
        {
            Value = value;
        }
    }

    public class DestInner2
    {
        public int Value { get; }

        public DestInner2(int value)
        {
            Value = value;
        }
    }
}

Mapping configuration

protected override MapperConfiguration Configuration { get; } = new MapperConfiguration(config =>
{
    config.CreateMap<Source, Dest>()
        .ForCtorParam("inner2", cfg => cfg.MapFrom(_ => new Dest.DestInner2(100)));
});

Version: 8.1.1

Expected behavior

Destination.Details should contain an instance of DestInner2.

Actual behavior

AutoMapper.AutoMapperConfigurationException: 'Dest does not have a constructor with a parameter named 'inner2'.

Steps to reproduce

public void Should_redirect_value()
{
    var dest = Mapper.Map<Source, Dest>(new Source("Success"));

    dest.ShouldNotBeNull();
}

I have been looking into this issue, and following the comments in #2745, I added a dummy "inner2" parameter to the Source object, which causes MapDestinationPropertyToSource in TypeMapFactory to pass.

However, because Dest has two constructors, one accepting an instance of inner1 and the other inner2, I would need to have both dummy parameters in Source.

Unfortunately, due to the way that constructor mapping is achieved, the first constructor always passes, so it always hits the "cannot find a constructor with parameter 'inner2'" error.

I note that the previous person to report this was asked to submit a PR last August and hasn't done so, so I have looked into it myself. I have a working prototype, but I don't know the codebase anywhere near well enough to know if I'm missing things.

All existing tests still pass, as does the one I have added to Constructor.cs.

Any assistance would be appreciated.

[lbargaoanu]

Try the MyGet build.

[spydacarnage]

No change. Without the workaround properties, it works for "inner2" but not "inner1"; with the workaround properties, it works for "inner1" but not "inner2".

[lbargaoanu]

I've executed the code you posted and it works for me. So write smth I can execute and assert exactly what doesn't work.

[spydacarnage]

As I've downloaded the MyGet build into my main project (as opposed to running this against the source), so I've had to rewrite the tests slightly (I'm using xUnit), but they still achieve the same goals. I've included all 4 possible scenarios - going from the original Source to Destination1 and 2, and then from the SourceWithWorkaround (the dummy properties) to Destination1 and 2. Tests Source_to_Destination_2 and Workaround_to_Destination_1 work, the other two don't.

[lbargaoanu]

OK, I see the failing tests. The Dest constructor doesn't match, but you want to say that you have ForCtorParam and now it should match. Isn't it simpler to just use ConstructUsing? :) Anyway, if you'd prefer ForCtorParam, open a PR.

[spydacarnage]

Unfortunately, this two-property constructor is a highly simplified version of the actual code to demonstrate what is failing - the full version is much longer, and if I wanted to manually write the full constructor, I could just run the constructor directly.

In the original issue, you suggested that code could be added to the TypeMapFactory class to fix this problem - is that not still the case? I mean, I can understand why it hasn't been done - ForCtorParam entries are buried in a web of interfaces and non-public properties.

I'll submit what I've done for you to critique and offer improvements, as you obviously know the codebase a lot better than I do!

[lbargaoanu]

Closing in favor of the PR.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.