Automapper 多对多关系

Question

I have a following Entity and Dto structure

public class Product
        {
            public int Id { get; set; }
            public string Name { get; set; }

            public ICollection<ProductProviders> ProductProviders { get; set; } = new HashSet<ProductProviders>();
        }

        public class ProductProviders
        {
            public int Id { get; set; }
            public int ProviderId { get; set; }
            public int ProductId { get; set; }

            public Provider Provider { get; set; }
            public Product Product { get; set; }
        }

        public class Provider
        {
            public int Id { get; set; }
            public string Name { get; set; }
            public string Address { get; set; }

            public ICollection<Product> Products { get; set; } = new HashSet<Product>();
        }

        public class ProductDto
        {
            public int Id { get; set; }
            public string Name { get; set; }

            public List<ProductProvidersDto> Providers { get; set; }
        }

        public class ProductProvidersDto
        {
            public int Id { get; set; }
            public int ProviderId { get; set; }
            public int ProductId { get; set; }

            public ProviderDto Provider { get; set; }
            public ProductDto Product { get; set; }
        }

        public class ProviderDto
        {
            public int Id { get; set; }
            public string Name { get; set; }
            public string Address { get; set; }

            public List<ProductDto> Products { get; set; }
        }

Now when I am inserting an Product object into database, I would like for it to automatically insert corresponding records into ProductProviders table.

I have tried several sulutions from other posts here and some other sources, and last solution that I came up with was this-

CreateMap<ProductDto, Product>()
.ForMember(dest => dest.ProductProviders, opts => opts.MapFrom(r => r.Providers.Select(r => r.Provider.Id).ToList()));

But this is giving me back an error, saying that relation does not exist (but this is the closest one to success, I think).

To be clear:

1. DB relations are correct
2. All the necessary information is specified

Is there some way to fix this mapping, so that when I insert a Product into database, it also inserts records into ProductProviders table?

Answer 1

You can use AfterMap (see: https://docs.automapper.org/en/stable/Before-and-after-map-actions.html ) and write there logic to assign/fill needed fields in your own way:

.AfterMap((src, dest) =>
 {
   // write custom assignment logic etc.
 });