EF Core OrderBy 其他表上的引用计数

Question

I have a table with authors and a table with books.

public class Author
{
    public int ID { get; set; }
    public string Name { get; set; }
}

public class Book
{
    public int ID { get; set; }
    public string Name { get; set; }
    public Author Author { get; set; }
}

I want to order my Authors by the amount of Books they have. I need to Access the data via _context.Authors.XXX as I have additional filtering applied on the IQueryable .

I am using net5.0 and ef core 5.0.

Is there an 'elegant' way?

Thanks!

Answer 1

Add a Books nav property and map accordingly, something named like:

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

Then in your query:

_context.Authors.OrderByDescending(x => x.Books.Count());

Answer 2

you need to update both your Author and Book classes. The author class needs to include a navigational "Books" property which will hold a list of books by the Author, while the Book class will hold an AuthorId property which will serve as a foreign key to the Author table.

public class Book
{
    public int ID { get; set; }
    public string Name { get; set; }
    public string AuthorID {get; set; }
    public virtual Author Author { get; set; }
}

public class Author
{
    public Author() {
       this.Books = new List<Book>();
    }
    
    public int ID { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Book> Books { get; set; }
}