Mapping to child properties defined with auto-property pattern silently fails

Source/destination types

        class Child { }
        class ChildViewModel { }

        class Parent
        {
            public Parent()
            {
                Children = new List<Child>();
                NeglectedChildren = new List<Child>();
            }

            public ICollection<Child> Children { get; private set; }
            public ICollection<Child> NeglectedChildren { get; private set; }
        }

        class ParentViewModel
        {
            public ParentViewModel()
            {
                Children = new List<ChildViewModel>();
            }

            public ICollection<ChildViewModel> Children { get; private set; }
            public ICollection<ChildViewModel> NeglectedChildren { get; } = new List<ChildViewModel>();
        }

Mapping configuration

        private class TestProfile : Profile
        {
            public TestProfile()
            {
                CreateMap<Child, ChildViewModel>();
                CreateMap<Parent, ParentViewModel>();
            }
        }

Version: x.y.z

6.0.2

Expected behavior

I expect the ParentViewModel.NegelectedChildren collection to contain the same number of elements as source Parent.NeglectedChildren.

Actual behavior

ParentViewModel.NegelectedChildren is empty regardless of the number of elements in the source Parent.NegelectedChildren collection.

Steps to reproduce

Given a class with both a collection property defined with { get; private set; } and a collection property using the auto-property with initializer pattern:

        private IMapper _mapper;

        [TestInitialize]
        public void TestInitialize()
        {
            var config = new MapperConfiguration(cfg =>
            {
                cfg.AddProfile<TestProfile>();
            });

            _mapper = config.CreateMapper();
        }

        [TestMethod]
        public void WillPopulateAllElementsIntoChildrenCollection_WhenSourceChildrenIsNotEmpty()
        {
            // Arrange
            var packet = new Parent();
            packet.Children.Add(new Child());
            packet.Children.Add(new Child());
            packet.NeglectedChildren.Add(new Child());
            packet.NeglectedChildren.Add(new Child());
            
            // Act
            var result = _mapper.Map<ParentViewModel>(packet);

            // Assert
            result.ShouldSatisfyAllConditions(
                () => result.ShouldNotBeNull(),
                () => result.Children.Count.ShouldBe(2),
                () => result.NeglectedChildren.Count.ShouldBe(2));
        }

The test fails:

Test method WillPopulateAllElementsIntoChildrenCollection_WhenSourceChildrenIsNotEmpty threw exception: 
Shouldly.ShouldAssertException: result
    should satisfy all the conditions specified, but does not.
The following errors were found ...
--------------- Error 1 ---------------
    result.NeglectedChildren.Count
        should be
    2
        but was
    0

[jbogard]

I wonder, would adding a MapFrom along with UseDestinationValue work?

An aside, maybe it’s a bit weird that we just skip adding property maps that don’t have a setter vs. adding them and then deciding how to deal with it.

[lock[bot]]

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