👀 Views: 57 💬 Answers: 1 📅 Created: 2025-06-08

c# automapper dotnet collections C#

I've been researching this but I'm experiencing an issue with AutoMapper when trying to map a source object that has a nested collection to a destination object. The source object looks like this: ```csharp public class Author { public string Name { get; set; } public List<Book> Books { get; set; } } public class Book { public string Title { get; set; } public int Year { get; set; } } public class AuthorDto { public string Name { get; set; } public List<BookDto> Books { get; set; } } public class BookDto { public string Title { get; set; } public int Year { get; set; } } ``` I have set up my AutoMapper configuration like this: ```csharp var config = new MapperConfiguration(cfg => { cfg.CreateMap<Author, AuthorDto>(); cfg.CreateMap<Book, BookDto>(); }); var mapper = config.CreateMapper(); ``` However, when I try to map an `Author` object that has a list of `Book` objects, the `Books` list in the `AuthorDto` comes out empty. Here’s how I’m doing the mapping: ```csharp var author = new Author { Name = "John Doe", Books = new List<Book> { new Book { Title = "C# in Depth", Year = 2021 }, new Book { Title = "Clean Code", Year = 2018 } } }; var authorDto = mapper.Map<AuthorDto>(author); ``` Despite the source `Author` object being correctly populated, the `authorDto.Books` ends up as an empty list. I’ve verified that the `Books` collection in the `Author` is not null or empty before mapping. I’ve also tried using `.ToList()` on the Books property in the configuration, but that didn't resolve the issue. Does anyone have insights on why the mapping is not correctly populating the nested collection? Is there a specific configuration I’m missing in AutoMapper that could cause this behavior? I’m using AutoMapper version 10.1.1 with .NET 5.0, and I’ve ensured all the necessary namespaces are included. Any help would be greatly appreciated! This issue appeared after updating to C# 3.9. Thanks for any help you can provide!