Adding Default Constructor parameter to record using Automapper

Question

Im trying to use automapper to map from one record to a new record and add a few defaults based on some logic. I was originally expecting "ForCtorParam" to work, but im still getting the same exception after adding it.

    public record Source(
        int number);
    public record Destination(
        int number,
        string numberAsString);
    [Fact]
    public void automapperTest()
    {
        var config = new MapperConfiguration(cfg =>
        {
            cfg.CreateMap<Source, Destination>()
            .ForCtorParam("numberAsString", (opt) => opt.MapFrom((src) => src.number.ToString()));
        });
        config.AssertConfigurationIsValid();
    }

Im not sure if i am trying to do something that is not intended or missunderstanding the automapper documentation.

Hoping someone in here can help TIA

Answer 1

Your code is going to work when mapping one record to another. However, the AssertConfigurationIsValid method is going to throw an error Unmapped properties: number, numberAsString.

For me, it helped to add the .ForAllMembers(opt => opt.Ignore()) at the end of the mapping. This will resolve the validation issue and the mapping is going to work as normal.

You can check that with a unit-test mapping the two records.