如何使用AutoMapper创建复杂的映射？

Question

I have the following Entity-Models

public class Blog 
{
    public int Id { get; set;}
    public string Title { get; set; }
    public string Body { get; set; }

    [ForeignKey("Category")]
    public int? CategoryId { get; set; }
    public virtual Category Category { get; set; }
    public virtual ICollection<Comment> Comments { get; set; }
}

public class Category
{
    public int Id { get; set;}

    public string Name { get; set; }
}

public class Comment
{
    public int Id { get; set;}

    public string Title { get; set; }
    public string Body { get; set; }
    [ForeignKey("Blog")]
    public int BlogId { get; set; }
    public virtual Blog Blog { get; set; }
}

Then I have the following view-model in which I like to tell AutoMapper to map the Blog object into the BlogViewModel notice the CategoryName property will need to come from Blog.Category.Name and each Comment in the Blog.Comments need to be converter to CommentViewModel using the organic convention.

I currently set the mapping at run time using reflection for any class that implements the ICustomMap interface. Please read the comment in the code over the Transfer(IMapper mapper) method.

public class BlogViewModel : ICustomMapFrom 
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Body { get; set; }
    public string MyCatName { get; set; }
    public IEnumerable<CommentViewModel> Comments { get; set; }

    // **IMPORTANT NOTE**
    // This method is called using reflection when the on Application_Start() method.
    // If IMapper is the wrong Interface to pass, I can change
    // the implementation of ICustomMap
    // I assumed that `IMapper` is what is needed to add configuration at runtime.
    public void Transfer(IConfigurationProvider config)
    {
        // How to I do the custom mapping for my MyCatName and Comments?
        // I need to use the config to create the complex mapping
        // AutoMapper.Mapper.Map(typeof(Blog), typeof(BlogViewModel));
    }
}

Finally here is my CommentViewModel

public class CommentViewModel : IMapFrom<Comment>
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Body { get; set; }
}

How can I tell AutoMapper how to map the CategoryName and the Comments?

Updated

Here is how I would create the mapping. I would have the following 3 interfaces

public interface IMap
{
}

public interface IMapFrom<T> : IMap
{
}

public interface ICustomMapFrom : IMap
{
    void Map(IConfigurationProvider config);
}

Then in the Global.cs file

I would execute the Run method on startup. Basically this method will scan assemblies and register the classes that I would want to register using the interfaces.

public class ConfigureAutoMapper 
{
    public void Run()
    {
        var types = AssemblyHelpers.GetInternalAssemblies()
                                   .SelectMany(x => x.GetTypes())
                                   .Where(x => x.IsClass && !x.IsAbstract && !x.IsInterface && typeof(IMap).IsAssignableFrom(x))
                                   .ToList();


        RegisterStandardMappings(types);
        RegisterCustomMappings(types);
    }

    private static void RegisterStandardMappings(IEnumerable<Type> types)
    {
        foreach (Type type in types)
        {
            if(type.IsGenericType && typeof(IMapFrom<>).IsAssignableFrom(type))
            {
                AutoMapper.Mapper.Map(type.GetGenericArguments()[0], type);
            }
        }
    }

    private static void RegisterCustomMappings(IEnumerable<Type> types)
    {
        foreach (Type type in types)
        {
            if (typeof(ICustomMapFrom).IsAssignableFrom(type))
            {
                ICustomMapFrom map = (ICustomMapFrom)Activator.CreateInstance(type);
                var t = AutoMapper.Mapper.Configuration;

                map.Map(Mapper.Configuration);
            }
        }
    }
}

Answer 1

I wrote an NUnit test which sets up AutoMapper with your classes. AutoMapper supports the mapping of CategoryName out of the box.

[TestFixture]
public class TestClass
{
    [Test]
    public void Test1()
    {
        var config = new MapperConfiguration(cfg =>
        {
            cfg.CreateMap<Blog, BlogViewModel>();
        });

        config.AssertConfigurationIsValid();

        var blog = new Blog()
        {
            Body = "Blog body",
            Category = new Category { Name = "My Category" },
            Comments = new List<Comment>() {
                new Comment { Body = "Comment body 1" },
                new Comment { Body = "Comment body 2" }
            }
        };

        var mapper = config.CreateMapper();
        var result = mapper.Map<Blog, BlogViewModel>(blog);

        Assert.AreEqual(blog.Body, "Blog body");
        Assert.AreEqual(blog.Category.Name, result.CategoryName);
        List<CommentViewModel> comments = result.Comments.ToList();
        Assert.That(comments.Any(c => c.Body == "Comment body 1"));
        Assert.That(comments.Any(c => c.Body == "Comment body 2"));
    }
}