ProjectLib/ProjectLibrary/Entites/Book_library.cs

using System.ComponentModel;

namespace ProjectLibrary.Entites
{
    public class Book_Library
    {
        public int BookID { get; private set; }

        public int LibraryID { get; private set; }
        [DisplayName("Количество")]
        public int Count { get; private set; }

        public static Book_Library CreateEntity(int libraryID, int bookID, int count)
        {
            return new Book_Library
            {
                BookID = bookID,
                LibraryID = libraryID,
                Count = count
            };
        }
    }
}