Multi tool use

Is there a shorter, better and optimised way to fill this list from SQL database

I got this code and it works without problems. But i sense there is much better way to do this.

namespace Repositories
{
public class AuthorRepository : IAuthorRepository
{
public List<Author> GetAllFromRepo()
{
using (AppContext myDB = new AppContext())
{
List<Author> authorsFromRepo = new List<Author>();
foreach (var item in myDB.Authors)
{
authorsFromRepo.Add(new Author()
{
Books = new List<Book>(),
ID = item.ID,
FirstName = item.FirstName,
LastName = item.LastName
});
}
return authorsFromRepo.ToList();
}
}
}
}


When i try something along the lines of this:

public List<Author> GetAllFromRepo()
{
using (AppContext myDB = new AppContext())
{
List<Author> authorsFromRepo = new List<Author>();

authorsFromRepo = myDB.Authors.ToList();
return authorsFromRepo;
}
}


I always get this error:

Value cannot be null.
Parameter name: source
Exception Details: System.ArgumentNullException: Value cannot be null.
Parameter name: source
Source Error: Line 33: return authors.Select(x => new AuthorViewModel()

Any Help?
The model where the error takes me

namespace Services
{
public class AuthorService : IAuthorService
{
private readonly IAuthorRepository _AuthorRepository;

public AuthorService(IAuthorRepository authorRepository)
{
_AuthorRepository = authorRepository;
}
public List<AuthorViewModel> GetAll()
{
List<Author> authors = _AuthorRepository.GetAllFromRepo();

return authors.Select(x => new AuthorViewModel()
{
ID = x.ID,
FullName = $"{x.FirstName } {x.LastName} ",
Books = x.Books.Select(g => new BookViewModel()
{
ID = g.ID,
Name = g.Name
}).ToList()
}).ToList();

}
}
}


To add again, everything works fine if i use the first example of code.
When i try something shorter like

return myDB.Authors.ToList();


i get the error.

when i change to:

return authors.Select(x => new AuthorViewModel()
{
ID = x.ID,
FullName = $"{x.FirstName } {x.LastName} ",
Books = {}
}).ToList();


It works then... but this means it doesn't read the author books...

AuthorViewModel

return myDB.Authors.ToList();

authors

List<Author> authors = _AuthorRepository.GetAllFromRepo();

null

Books

x.Books

null

Books = new List<Book>(),

x.Books

1 Answer
1

I had to change the model for Authors to

namespace Entities
{
public class Author
{
// this is what a had to add here
// From here
public Author()
{
Books = new List<Book>();
}
// to here

public int ID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }

public List<Book> Books { get; set; }
}
}


So It wont give me any errors when x.Books is null.

Author.Books

Enumerable.Empty<Book>()

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