//Model ProductDetail
public class ProductDetail
    {
        public virtual Product Product { get; set; }
        public virtual Category Category { get; set; }

        public int Count { get; set; }
    }

//Model Product
public class Product
{
[Required] public string Name { get; set; }

public virtual IEnumerable<ProductDetail> ProductDetail { get; set; }

}

//Model Category (Вдруг надо).
public class Category
{
   public string ImageUrl { get; set; }

   public virtual IEnumerable<ProductDetail> ProductDetail { get; set; }
}

P.S связь тут много к многому

//Controller

var blog2 = _context.ProductDetails
                .Include(b => b.Product)
                .ThenInclude(p => p.Name)
                .FirstOrDefault();

ViewData["Titles"] = blog2;