public class Repository<T> where T : class
{
    private readonly LibraryContext context;
    private IDbSet<T> entities;

    public Repository(LibraryContext context)
    {
        this.context = context;
    }

public class BookService
{
    LibraryContext context = new LibraryContext();

    private Repository<Book> bookRepository;
    private Repository<PublicationHouse> publicationHouseRepository;

    public BookService()
    {
        bookRepository = new Repository<Book>(context);
        publicationHouseRepository = new Repository<PublicationHouse>(context);
    }