I created local database using EF core and code-first method. The db imitates library, so I have 3 simple tables: users, books and reservations.

Issue occurs when I want to get nested data like find one book and get its reservation. I think I should be able to use

List<Reservation> reservations = book.Reservations;

but I have to use

List<Reservation> reservations = libraryContext.Reservations.
   Where(r=> r.Book == book).ToList();

But the main reason I need help is this fragment

BookReservationsModel bookReservationsModel = new BookReservationsModel
{
    BookTitle = book.Title,
    Reservations = reservations
};

// I want to display emails in View.
for (int i = 0; i < bookReservationsModel.Reservations.Count; i  )
{
    Debug.WriteLine(bookReservationsModel.Reservations[i].User.Email);
}

I cannot get access to users because they are nulls. In database everything is stored as it should be (correct ids). Of course I could copypaste certain emails to new created list but it's inefficient and I know I should be able to use it that way. I worked before with EF for Framework and I tried google the problem but couldn't find the solution.

Models and context code.

public class User
    {
        [Key]
        public int UserID { get; set; }

        [Required]
        public string Name { get; set; }

        [Required]
        public string LastName { get; set; }

        [Required]
        public string Email { get; set; }

        [Required]
        public string Salt { get; set; }

        [Required]
        public string Password { get; set; }

        public ICollection<Reservation> Reservations { get; set; }
    }

public class Book
    {
        [Key]
        public int BookID { get; set; }

        [Required]
        public string Title { get; set; }

        [Required]
        public string Author { get; set; }

        [Required]
        [DataType(DataType.Date)]
        public DateTime PublishDate { get; set; }

        [Required]
        public string Description { get; set; }

        public ICollection<Reservation> Reservations { get; set; }
    }

public class Reservation
    {
        [Key]
        public int ReservationID { get; set; }

        [Required]
        public DateTime ReservationDate { get; set; }

        [Required]
        public int UserID { get; set; }
        [ForeignKey("UserID")]
        public User User { get; set; }
        [Required]
        public int BookID { get; set; }
        [ForeignKey("BookID")]
        public Book Book { get; set; }
    }

public class LibraryContext : DbContext
    {
        public LibraryContext(DbContextOptions options) : base(options) { }

        public DbSet<User> Users { get; set; }
        public DbSet<Book> Books { get; set; }
        public DbSet<Reservation> Reservations { get; set; }
    }

CodePudding user response：

Attempting to use a navigation property on the book entity without doing either of the following will result in the property being null.

• Including the property before materializing the entity with .First()/.Single()
  • https://docs.microsoft.com/en-us/ef/core/querying/related-data/eager
• Configuring EFCore to AutoInclude navigation properties by default.
  • https://dotnetcoretutorials.com/2021/03/07/eager-load-navigation-properties-by-default-in-ef-core/

I suggest when querying for the book to use the Include and ThenInclude methods so the Reservations and Users are populated.

var book = await libraryContext.Books
    .Include(x => x.Reservations)
        .ThenInclude(x => x.User)
    .SingleAsync(x => x.BookID == myBookId);